Automated electric drive course of lectures. Variable frequency asynchronous electric drive - a course of lectures. Electric drive and automation of industrial installations and technological complexes
Kharkiv National Academy of Municipal Economy
LECTURE NOTES
by discipline
"Automated electric drive"
(for students of the 4th year of full-time and part-time education in the specialty 6.090603 - "Electrical systems of power supply")
Kharkiv - HNAGH - 2007
Abstract of lectures on the discipline "Automated electric drive" (for 4th year students of all forms of education of the specialty 6.090603 - "Electrical power supply systems"). Auth. Garyazh V.N., Fateev V.N. - Kharkov: KhNAGH, 2007. - 104 pages.
CONTENT
| General characteristics of the lecture notes |
||
| Content module 1. Automated electric drive - the basis for the development of the productive forces of Ukraine. . . . . . . . . . . . | ||
| Lecture 1 | ||
| 1.1. | Development of the electric drive as a branch of science and technology. . . . . . | 6 |
| 1.2. | Principles of construction of control systems Automated electric drive. . . . . . . . . . . . . . . . . . . | |
| Lecture 2 | ||
| 1.3. | Classification of AEP control systems. . . . . . . . . . . . . . . . . . | 13 |
| Content module 2. Electric drive mechanics . . . . . . . . . . | 18 |
|
| Lecture 3 | ||
| 2.1. | Bringing the moments and forces of resistance, moments of inertia. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . | |
| Lecture 4 | ||
| 2.2. | The equation of motion of the electric drive. . . . . . . . . . . . . . . . . . . . . | 21 |
| Lecture 5 | ||
| 2.3. | Mechanical characteristics of a DC motor of independent excitation. motor mode. . . . . . . . . . . | |
| Lecture 6 | ||
| 2.4. | Mechanical characteristics of a DC motor of independent excitation. Electric braking mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . | |
| Lecture 7 | ||
| 2.5. | Mechanical characteristics of a series-excited DC motor. motor mode. . . . . . | |
| Lecture 8 | ||
| 2.6. | Mechanical characteristics of a series-excited DC motor. Electric braking mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . | |
| Lecture 9 | ||
| 2.7. | Mechanical characteristics of asynchronous motors. motor mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . | |
| Lecture 10 | ||
| 2.8. | Mechanical characteristics of asynchronous motors. Electric braking mode. . . . . . . . . . . . . . . . . . .. . . . . | |
| Lecture 11 | ||
| 2.9. | Mechanical and electrical characteristics of synchronous motors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . | |
| Content module 3. typical units of automatic motor control circuits. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . | ||
| Lecture 12 | ||
| 3.1. | Principles of automatic control of starting and braking of engines. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . | |
| Lecture 13 | ||
| 3.2. | Typical nodes of automatic control circuits for starting DPT. | 77 |
| Lecture 14 | ||
| 3.3. | Typical units of circuits for automatic control of DPT braking. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . | |
| Lecture 15 | ||
| 3.4. | Typical nodes of automatic control circuits for starting AC motors. . . . . . . . . . . . . . . . . . . . . . . . . . . . | |
| Lecture 16 | ||
| 3.5. | Typical nodes of circuits for automatic control of braking of AC motors. . . . . . . . . . . . . . . . | |
| Lecture 17 | ||
| 3.6. | Units of electrical protection of motors and control circuits. . . | 98 |
GENERAL CHARACTERISTICS OF THE LECTURE SUMMARY
The automated electric drive is the main consumer of electricity. In industrialized countries, more than 65% of the generated electricity is converted by an electric drive into mechanical energy. Therefore, the development and improvement of the electric drive, which is the basis of the energy-to-weight ratio of labor, contributes to productivity growth and production efficiency. Knowledge of the properties and capabilities of the electric drive allows the electrical engineer to ensure the rational use of the electric drive, taking into account the requirements of both technological machines and power supply systems. The subject "Automated electric drive" is studied in the seventh semester of the fourth year of study. The curriculum of the specialty "Electrotechnical systems of power consumption" allocated four credits for it. They are filled with six meaningful modules that are studied during lectures and practical classes, when performing laboratory work and a calculation and graphic task.
This lecture notes provide material for studying the first three content modules of the subject “Automated electric drive”. In the first content module, an automated electric drive is considered as the basis for the development of the productive forces of Ukraine. In the second, the mechanical characteristics of the engines are studied, showing the capabilities of the engine during operation, both in the motor mode and in the electric braking mode. In the third module, typical components of automatic engine control circuits are studied. Based on the properties of motors studied in the second module, typical units provide automatic starting, braking and reversing of motors in the functions of time, speed and current with direct or indirect control of these quantities. Structurally, typical nodes are combined in the form of control stations. The share of control stations in the total number of electric drives used in Ukraine exceeds 80%.
Lecture 1
1.1. The development of the electric drive as a branch of science and technology
Since ancient times, man has sought to replace hard physical labor, which was a source of mechanical energy (ME), with the work of mechanisms and machines. To do this, in transport and agricultural work, in mills and irrigation systems, he used the muscular strength of animals, the energy of wind and water, and later the chemical energy of fuel. This is how a drive appeared - a device consisting of three significantly different parts: an engine (D), a mechanical transmission device (MPU) and a technological machine (TM).
The purpose of the engine: the conversion of various types of energy into mechanical energy. MPU is designed to transfer the ME from the engine to the TM. It does not affect the amount of transmitted ME (without taking into account losses), but it can change its parameters and, to coordinate the types of movement, it is performed in the form of a belt, chain, gear or other mechanical transmission.
In a technological machine, ME is used to change the properties, state, shape or position of the material or product being processed.
In modern drives, various electric motors (EM) are used as a source of ME. They convert electrical energy (EE) into mechanical energy and therefore the drive is called an electric drive (EA). Its functional diagram is shown in fig. 1.1. In addition to the named elements, its composition includes a controlled converter (P), with the help of which EE is supplied from the network to the ED.
By changing the converter control signal U at, you can change the amount of EE coming from the network to the ED. As a result, the amount of ME produced by the engine and received by HM will change. This, in turn, will lead to a change in the technological process, the efficiency of which is characterized by an adjustable value y(t).
The priority in the creation of an electric drive belongs to Russian scientists
B.S. Jacobi and E.H. Lenz, who in 1834 invented the DC motor, and in 1838 used it to propel boats. However, the imperfection of the engine and the uneconomical source of electrical energy (galvanic battery) did not allow this electric drive to find practical application.
In the middle of the 19th century, attempts to use ED with a DC motor for printing and weaving machines were made by scientists from France and Italy. However, the DC system did not provide a satisfactory solution. By 1890, only 5% of the total drive motor power was electric motors.
The widespread use of the electric drive is associated with the invention in 1889-1891 by the Russian engineer Dolivo-Dobrovolsky of a three-phase alternating current system and a three-phase asynchronous motor. The simplicity of the three-phase system, the possibility of centralized production of electricity, the convenience of its distribution led to the fact that by 1927, already 75% of the total power of drive motors were electric motors.
Currently, in the leading industries, the ratio of the installed power of electric drives to the total installed power of drives with engines of all types (thermal, hydraulic, pneumatic) is approaching 100%. This is determined by the fact that electric motors are manufactured for a variety of capacities (from hundredths of a watt to tens of thousands of kilowatts) and rotation speeds (from fractions of a shaft revolution per minute to several hundred thousand revolutions per minute); EP operates in the environment of aggressive liquids and gases at low and high temperatures; due to the controllability of the converter, the EA easily regulates the course of the technological process, providing various parameters of the movement of the working bodies of the TM; it has high efficiency, is reliable in operation and does not pollute the environment.
Currently, the total installed capacity of electric generators in Ukraine exceeds 50 million kW. Electric networks have also been created to distribute such power at all voltage levels.
However, due to the decline, first of all, of industrial production, real electricity consumption in Ukraine is provided at the expense of half of the specified capacity. Such a significant energy reserve is a reliable basis for the development of the productive forces of Ukraine, associated with the introduction of new energy-saving technologies, the production of modern high-tech products, the further development of automation and mechanization of production. The solution of all, without exception, the above tasks is ensured by the use of various electric drive systems, an increase in the consumption of electric energy by the electric drive, which in the existing consumption structure is already approaching 70%.
1.2. Principles of building control systems for automated electric drives
A distinctive feature of a modern electric drive is that it contains a converter control signal U at is formed by a special automatic control device (AUD) without the direct participation of a person. Such control is called automatic, and the electric drive is called automated (AED).
The AED control system, like any other automatic control system, can be considered as a system that receives and processes information.
The first channel generates information about the required value of the controlled variable q(t)(setting influence).
In the second channel, with the help of sensors, information about the actual value of the controlled variable can be obtained. y(t) or other values characterizing the EP.
The third channel can provide information about disturbing influences to the control system f i (t) as a signal x i (t).
Depending on the number of information channels used, there are three principles for constructing control systems for an automated electric drive:
1) the principle of open control;
2) the principle of closed control;
3) the principle of combined management.
Let's consider functional diagrams of AED control systems.
The AED control system, built on the principle of open control, is called an open system. It uses only one channel of information - about the required value of the controlled variable q(t). The functional diagram of such a control system is shown in Figure 1.2.
As in the previous case, the summation node at the ACU input receives information about q(t). Arrow indicating q(t), is directed to the unshaded sector of the summation node. This means that the setting signal enters the summation node with the “+” sign.
Automatic control device generates a signal to control the converter U y, using only information about the value of the driving force q(t), which is supplied to the ACU input from the command body (CO). As a result of the fact that each element of the functional diagram is influenced by perturbing influences f i (t), the amount of mechanical energy supplied to the technological machine, and hence the stroke
Rice. 1.2 - Functional diagram of an open-loop control system for AED
technological operations will change. As a result, the actual value of the controlled variable y(t) may differ significantly from the required value q(t). The difference between the desired and the actual value of the controlled variable in steady state (when the controlled variable y(t) does not change with time) is called control error Δx(t)=q(t)–y(t).
Open-loop AED systems are used in the event that the appearance of a control error does not lead to significant losses in technology (decrease in TM productivity, decrease in product quality, etc.)
Otherwise, when the appearance of a control error significantly reduces the efficiency of the technological process, the principle of closed control is used to build the AED control system. Such a system is called a closed system.
It uses two channels of information: to information about the required value of the controlled variable q(t) information about the actual value of the controlled variable is added y(t). The functional diagram of such a control system is shown in Figure 1.3.
Information about the actual value of the controlled variable y(t) is fed to the summation node using the main feedback (GOS). It is said that the GOS "closes" the control system by connecting its output to the input.
Arrow indicating y(t), is directed to the shaded sector of the summation node, i.e. the GOS signal enters the summation node with the “-” sign and therefore the GOS is called negative feedback.
Rice. 1.3 - Functional diagram of the closed control system of the AED.
In the summation node as a result of algebraic (taking into account the sign) addition of signals q(t) and y(t) the magnitude and sign of the control error are determined Δx(t)= +q(t) – y(t). The error signal is fed to the input of the ACU. Thanks to this, the ACU, by generating a control signal for the converter P on the basis of information about the actually existing ratio of the setpoint and the actual value of the controlled variable, provides the supply of such an amount of EE to the ED, and to the ME technological machine, that the control error can be reduced to an acceptable value or reduced to zero.
In addition to the GOS, in the control system there can be various feedbacks internal to the GOS (FOS). They control the intermediate parameters of the system, which improves the quality of the control process. A system containing only GOS is called single-loop, and having, in addition to GOS, also VOS, is called multi-loop.
In a system built according to the combined principle, two structures are combined - closed and open. To the closed system, which is the main one, an open structure is added via the third information channel x 1 (t) about the main disturbing effect f 1 (t). The functional diagram of the system is shown in Figure 1.4.
The main one is the perturbing effect, which has the largest component in the magnitude of the control error.
Rice. 1.4 - Functional diagram of the combined AED control system
On fig. 1.4 for the main one, the perturbing effect is taken f 1 (t). It is controlled by an intermediate element (PE) and information about it x 1 (t) fed into the summation node. Due to this, the ACU introduces a component into the converter control signal, which compensates for the influence f 1 (t) on the technological process and reduces the amount of control error. The influence of other perturbing influences on the error is eliminated by the main closed system.
The considered examples allow us to define the concept of "automated electric drive".
An automated electric drive is an electromechanical system in which, firstly, the conversion of electrical energy into mechanical energy is carried out. Through this energy, the working bodies of the technological machine are set in motion. And, secondly, the process of energy conversion is controlled in order to provide the required steady-state and transient operating modes of the TM.
Lecture 2
1.3. Classification of AEP control systems
The classification of AED control systems can be carried out according to many criteria: according to the type of motor current, the systems are divided into alternating and direct current. By type of information and control signals - into continuous and discrete systems. Depending on the nature of the equations describing the control processes - into linear and non-linear systems. Often they are subdivided according to the type of converter or main equipment: system - DC generator - engine (G-D); system - thyristor converter - motor (TP-D); system - thyristor frequency converter - motor (TPCh-D), etc.
However, the classification of AED control systems according to the functions they perform in technological processes has become most widespread. There are five such functions.
1. Systems for controlling the processes of starting, braking, reversing. Among them, in turn, three groups of systems can be distinguished.
Systems of the first group are open. They are used in electric drives with asynchronous motors with a squirrel-cage rotor. The converter consists of a power switching device (SPU) that connects the motor directly to the network. All control equipment - relay action (contact or non-contact).
Control systems of the second group are also open-loop. They are used in electric drives with DC motors and asynchronous motors with a phase rotor, they have a more complex structure of the STC, which provide stepped switching of resistors or other elements in the power circuits of the motor. They provide automatic start and stop control, which limits the motor current and torque. With manual control of the SPU, it is possible to control the speed in a small range.
Systems of the third group are intended for the implementation of optimal processes of starting, braking, reversing. Optimal in this case is understood as transient processes occurring in the minimum time. This is ensured by maintaining the value of the engine torque at the level of the permissible value during the starting and braking process.
Such systems are used in electric drives with intermittent operation, when the time of the steady state is short or completely absent. Therefore, the appearance of a control error will not lead to losses in technology, and the system may not have a GOS.
A closed control loop in such a system is formed by negative feedback on the torque (current) of the motor. In Figure 1.4, it is shown as BOS. In this case, the motor torque becomes the controlled variable. Therefore, the ACU generates a control signal P in such a way that during the process of starting and braking, the torque is maintained at the required level or changes in time according to the required law.
2. Systems for maintaining a constant set value of the controlled variable (stabilization systems). The adjustable values are those characterizing the movement of the working body of the TM and the motor shaft - speed, acceleration, torque, power, etc.
Stabilization systems are built on a closed principle and can have a functional diagram shown in Fig. 1.4. In such a system, the driving signal q(t)=const. Therefore, reducing the controlled variable y(t), caused by the appearance of a perturbing effect f 1 (t), will lead to an increase in the control error signal at the ACU input. The automatic control device generates a converter control signal depending on the control law applied in it (regulator type). With a proportional control law, a proportional (amplifying) link with a gain greater than unity is used as a regulator (P - regulator). Therefore, with an increase in the signal, the error at the input of the P - controller will increase and the control signal of the converter. As a result, the amount of EE and ME will increase, which will lead to an increase in y(t) and reducing control error. However, it cannot be fully compensated, since in this case the signals at the input and output of the P-regulator will be equal to zero, the EE will not be supplied to the engine and the technological process will stop.
A stabilization system in which the control error does not reduce to zero, but only decreases to an acceptable value, is called static.
With a proportional - integral control law, the regulator consists of two links connected in parallel - proportional and integral (P-I - regulator). The error signal arrives simultaneously at the input of both links. The proportional part of the regulator, as in the previous case, will amplify the error signal. The integral part of the controller will sum up the error signal, i.e. its output will increase as long as there is an error signal at the controller input. Since the output signal of the controller (converter control signal) is the sum of the output signals of the proportional and integral parts, as long as there is an error signal at the input of the controller, its output signal will increase. As a result, the amount of EE and ME in the system will increase and the control error will decrease. When the error signal at the controller input becomes equal to zero, the signal at the controller output will be greater than zero, due to the fact that the integral part of the controller, after the signal disappears at its input, remembers the total value of the output signal. EE will be supplied to the engine and the technological process will continue.
A stabilization system in which the control error is reduced to zero is called astatic.
With a proportional - integral - differential control law, parallel to the P, I. - links include a differentiating link (P - I - D - regulator).
The output signal of the differential part is directly proportional to the rate of change of the control error signal. Summing up with the signals of the P, I parts of the regulator, it additionally increases the converter control signal and the amount of EE supplied to the motor. This helps to reduce the dynamic control error, i.e. the difference between the desired and the actual value of the controlled variable during the transient in the system.
Stabilization systems are used in cases where it is necessary to maintain a particularly precise process parameter, as well as when regulating the engine speed in a wide range.
To form the processes of starting and braking, the stabilization system can have internal feedback on the motor torque (BOS in Fig. 1.4).
An open control channel for the main disturbing effect reduces the control error in static systems.
3. Tracking systems. Like stabilization systems, they are built on a closed principle. However, the driving signal q(t) they change according to a random law and the actual value of the controlled variable y(t) should repeat (track) this law.
They are used in technological machines that require that when the input shaft is rotated through any angle, the output shaft “follows” the input and rotates by the same angle.
When the positions of the shafts match q(t) = y(t) and the control error is zero. When changing the position of the input shaft q(t) ≠ y(t). An error signal appears at the ACU input, the converter supplies EE to the motor and the output shaft will rotate until it takes the input position.
4. Program control systems. They are used in technological machines with several electric drives. These drives can be built in both open-loop and closed-loop configurations. Common to them is a device that changes the set value of the regulated value of each electric drive according to a predetermined program. At the same time, the motors of individual working bodies automatically start, work at specified speeds or reverse, and the moving working bodies of the technological machine do not interfere with each other.
5. Adaptive systems. They are used in cases where a system built according to a closed principle, as a result of unforeseen changes in disturbing influences, is not able to perform its function, for example, stabilization of the controlled variable.
To ensure the adaptation (adjustability) of a closed system, an additional circuit is introduced into its composition, the basis of which is a computing device. It controls the amount q(t), y(t), disturbing influences f i (t), analyzes the operation of the stabilization system and determines the changes in the parameters or structure of the ACU necessary for adaptation.
Lecture 3
2.1. Reduction of moments and forces of resistance, moments of inertia and inertial masses
The mechanical part of the electric drive includes the rotating part of the engine, the mechanical transmission device and the working body of the technological machine.
The rotating part of the engine (armature or rotor) serves as a source of mechanical energy.
With the help of the MPU, the rotational motion of the engine is converted into the translational movement of the working body of the TM, or by changing the ratio of the speeds of the input and output shafts of the MPU, the speeds of rotation of the engine and the working body are coordinated. As MPU can be used cylindrical and worm gears, planetary gear, screw-nut pair, crank, rack, belt and chain gears.
The working body of the TM is a consumer of mechanical energy, which it converts into useful work. Among the working bodies include the spindle of a lathe or drilling machine, the moving part of the conveyor, the excavator bucket, the elevator cabin, the ship propeller, etc.
The elements of the mechanical part of the EP are connected to each other and form a kinematic chain, each element of which has its own speed of movement, is characterized by a moment of inertia or inertial mass, as well as a set of moments or forces acting on it. The mechanical motion of any of the elements is determined by Newton's second law. For an element rotating around a fixed axis, the equation of motion is:
Where 
is the vector sum of the moments acting on the element;
J is the moment of inertia of the element;
is the angular acceleration of the rotating element.
For a translationally moving element, the equation of motion has the form:
,
Where 
is the vector sum of the forces acting on the element;
m is the inertial mass of the element;
– linear acceleration of a translationally moving element.
Using these equations, the interaction of any element with the rest of the kinematic chain can be taken into account. It is convenient to do this by bringing the moments and forces, as well as the moments of inertia and inertial masses. As a result of this operation (reduction), the real kinematic scheme is replaced by a calculated, energetically equivalent scheme, the basis of which is the element whose motion is being considered. As a rule, this element is the motor shaft M. This allows you to most fully explore the nature of the movement of the electric drive and its mode of operation. Knowing the parameters of the kinematic scheme, it is possible to determine the type of movement of the working body of the technological machine.
The reduction of the moments of resistance from one axis of rotation to another is based on the power balance in the system.
During the technological operation, the working body rotating on its axis at a speed ω m and creating a moment of resistance M cm, consumes power R m =M cm ω m. Power losses in the MPU are taken into account by dividing the value R m on efficiency transmission η P. This power is provided by an engine rotating at a speed ω and development moment M With, equal to the moment of resistance reduced to the axis of rotation of the motor shaft M cm. Based on the equality of powers, we get:
.
Then the expression for determining the reduced moment of resistance M With looks like:
,
Where 
- gear ratio of MPU.
Bringing the resistance forces is done in a similar way. If the translational speed of the working body TM is equal to υ m and during the technological operation, a resistance force is created F cm, then taking into account the efficiency MPU power balance equation will look like:
.
Reduced moment of resistance M With will be equal to:
,
Where 
is the reduction radius of the MPU.
Each of the rotating elements of the kinematic scheme is characterized by the moment of inertia J і . Bringing the moments of inertia to one axis of rotation is based on the fact that the total kinetic energy of the moving parts of the drive, referred to one axis, remains unchanged. In the presence of rotating parts with moments of inertia J d , J 1 , J 2 , … J n and angular speeds ω, ω 1 , ω 2 , … ω n it is possible to replace their dynamic action by the action of a single element having a moment of inertia J and rotating at a speed ω .
In this case, we can write the kinetic energy balance equation:
.
The total moment of inertia reduced to the motor shaft will be equal to:
,
Where J d- the moment of inertia of the rotor (armature) M;
J 1 , J 2 , … J n are the moments of inertia of the remaining elements of the kinematic scheme.
Bringing inertial masses m, moving translationally, is also carried out on the basis of the equality of kinetic energy:
,
Hence, the moment of inertia reduced to the motor shaft will be equal to:
.
As a result of the reduction operations, the real kinematic scheme is replaced by a calculated, energetically equivalent scheme. It is a body rotating on a fixed axis. This axis is the axis of rotation of the motor shaft. It is acted upon by the engine torque M and the reduced moment of resistance M With. The body rotates at the speed of the engine ω and has a reduced moment of inertia J.
In the theory of an electric drive, such a design scheme is called a single-mass mechanical system. It corresponds to the mechanical part of the AED with absolutely rigid elements and without gaps.
In the tutorial that is brought to your attention, the tutorial will focus on the basics of the electric drive and its most promising form - an asynchronous frequency-controlled electric drive. The manual is intended for workers involved in the promotion of complex electrical products on the market, which is automated electric drives and for students of electrical specialties.
Lecturer: Onishchenko Georgy Borisovich. Doctor of technical sciences, professor. Full member of the Academy of Electrotechnical Sciences of the Russian Federation.
The series of video lectures covers the following topics:
1. Functions and structure of an automated electric drive.
2. General characteristics of an adjustable electric drive.
3. The principle of operation of an asynchronous motor.
4. Frequency regulation of the speed of an asynchronous motor.
5. Power controlled semiconductor devices.
6. Structural diagram of the frequency converter.
7. Autonomous voltage inverter. The principle of pulse-width modulation.
8. Rectifier and DC link as part of the frequency converter.
9. Structural diagrams of regulation of frequency-controlled electric drive.
10. Features of high-voltage frequency converters.
11. Fields of application of frequency-controlled electric drive.
Consideration of these issues will allow you to get a fairly complete picture of the composition, principles of operation, circuit design, technical characteristics and areas of application of a frequency-controlled asynchronous electric drive.
Lecture 1. Functions and structure of an automated electric drive
The objectives of the first lecture are to give an idea of the role and importance of an automated electric drive in modern industrial production and in the country's electric power system.
Lecture 2. Adjustable electric drive - the main type of modern electric drive
General issues related to the creation and use of adjustable electric drives are considered.
Lecture 3. The principle of operation of an asynchronous electric motor
Design features and main characteristics of the most common electrical machines - asynchronous motors. These motors are widely used in industry, agriculture, public utilities and other fields. The power range of manufactured asynchronous motors is very wide - from hundreds of watts to several thousand kilowatts, but the principle of operation of these machines is the same for all sizes and modifications.
Lecture 4
The most effective way to control the speed of an induction motor is to change the frequency and amplitude of the three-phase voltage applied to the windings of the induction motor. In recent years, this control method has received the widest application for electric drives for various purposes, both low-voltage with voltages up to 400 V and high-voltage high-power drives with voltages of 6.0 and 10.0 kV.
This section outlines the principles of controlling the motor speed by changing the frequency of the input voltage, provides possible algorithms for changing not only the frequency, but also the voltage amplitude, and analyzes the drive characteristics obtained with the frequency control method.
Lecture 5. The principle of operation and structure of the frequency converter
The creation and mass production of fully controlled power semiconductor devices had a revolutionary impact on the development of many types of electrical equipment, primarily on the electric drive. New fully controllable semiconductor devices include insulated gate bipolar transistors (IGBTs) and combination gated thyristors. Based on them, it became possible to create frequency converters for powering AC motors and smooth regulation of their rotation speed. In this section, the characteristics of new power semiconductor devices are considered and their parameters are given.
Lecture 6. Scalar motor control systems
For electric drives operating with a limited speed control range and in cases where high speed and control accuracy are not required, simpler scalar control systems are used, which are discussed in this section.
Module No. 7 "Vector control of frequency-controlled electric drives"
Vector control of an asynchronous motor is based on fairly complex algorithms that reflect the representation of electromagnetic processes in the motor in vector form. In this lecture, we will try to present the basics of vector control in a somewhat simplified way, avoiding complex mathematical calculations.
There will be a continuation soon!
Lectures on the discipline "Automated electric drive" Literature 1. Chilikin M.G., Sandler A.S. General Electric Drive Course (EP).-6th ed. -M.: Energoizdat, - 576 p. 2. Moskalenko V.V. Electric drive - M .: Mastery; Higher School, -368 p. 3. Moskalenko V.V. Electric drive: Textbook for electrical engineering. specialist. -M.: Higher. school, - 430 p. 4. Handbook of automated electric drive / Ed. V.A. Eliseeva, A.V. Shiyansky.-M.: Energoatomizdat, 1983. – 616 p. 5. Moskalenko V.V. Automated electric drive: Textbook for universities.- M.: Energoatomizdat, p. 6. Klyuchev V.I. Theory of electric drive. - M.: Energoatomizdat, p. 7. GOST R-92. Electric drives. Terms and Definitions. Gosstandart of Russia. 8. Handbook of an electrical engineer with.-x. production / Tutorial.-M.: Informagrotech, p. 9. Guidelines for the implementation of laboratory work on the basics of the electric drive for students of the electrification faculty of agriculture. / Stavropol, SSAU, "AGRUS", - 45 p. 10. Savchenko P.I. Workshop on electric drive in agriculture. – M.: Kolos, p. Recommended sites on the Internet: Lectures on the discipline "Automated electric drive" Literature 1. Chilikin M.G., Sandler A.S. General Electric Drive Course (EP).-6th ed. -M.: Energoizdat, - 576 p. 2. Moskalenko V.V. Electric drive - M .: Mastery; Higher School, -368 p. 3. Moskalenko V.V. Electric drive: Textbook for electrical engineering. specialist. -M.: Higher. school, - 430 p. 4. Handbook of automated electric drive / Ed. V.A. Eliseeva, A.V. Shiyansky.-M.: Energoatomizdat, 1983. – 616 p. 5. Moskalenko V.V. Automated electric drive: Textbook for universities.- M.: Energoatomizdat, p. 6. Klyuchev V.I. Theory of electric drive. - M.: Energoatomizdat, p. 7. GOST R-92. Electric drives. Terms and Definitions. Gosstandart of Russia. 8. Handbook of an electrical engineer with.-x. production / Tutorial.-M.: Informagrotech, p. 9. Guidelines for the implementation of laboratory work on the basics of the electric drive for students of the electrification faculty of agriculture. / Stavropol, SSAU, "AGRUS", - 45 p. 10. Savchenko P.I. Workshop on electric drive in agriculture. – M.: Kolos, p. Recommended sites on the Internet:
Source of electrical energy (IEE) Control device (CU) Converter device (PRB) Electric motor device (EM) M Transmission device (TRD) Consumer of mechanical energy (PME) U,I,f d F d, V d M m (F m), ω m (V m) tasks Figure 3 - Structural diagram of the AED
3 Efficiency of AED As for any electromechanical device, an important indicator is the efficiency of AED = PRB · ED · PRD at rated load is 60-95%.
4 Advantages of AED 1) low noise level during operation; 2) absence of environmental pollution; 3) a wide range of powers and angular speeds of rotation; 4) the availability of regulation of the angular velocity of rotation and, accordingly, the performance of the process unit; 5) the relative ease of automation, installation, operation in comparison with heat engines, for example, internal combustion.
FEDERAL STATE EDUCATIONAL INSTITUTION OF HIGHER PROFESSIONAL EDUCATION STAVROPOL STATE AGRARIAN UNIVERSITY
AUTOMATED ELECTRIC DRIVE
LECTURE COURSE
for the specialty 110302.65 - "Electrification and automation of agriculture" full-time and part-time education
Automated electric drive: a course of lectures \ Comp. I.V.Atanov. - Stavropol: SSAU, department of PEESH, 2008. - 124 p.
This textbook consists of lectures on automated electric drive in accordance with the state standard of higher professional education in the direction 660300 - Agroengineering.
The course of lectures is intended for full-time and part-time students of the specialty 110302.65 - "Electrification and Automation of Agriculture" and can be used both in the classroom and in the independent work of students.
INTRODUCTION
The course of lectures was developed for the training of specialists in the specialty 110302.65 - "Electrification and automation of agriculture" in the direction 660300 - "Agricultural engineering".
The lecture material contains 15 lectures on the discipline "Automated electric drive" and is based on the two previous courses "Fundamentals of electric drive" and "Electric drive of agricultural. machines."
Particular attention in the presentation of the material is given to the means and systems for regulating the coordinates of AC and DC electric drives.
When presenting the material, various fonts and emphasis were used, which made it possible to structure the material and facilitate its assimilation.
An important element in the study of educational material is the system of abbreviations of terms, definitions often found in the text. These abbreviations are entered and deciphered as they are first mentioned.
The presented lecture material is based on numerous literary sources, the main of which are given in this manual, in the literature section.
www.privod.ru www.owen.ru www.kipservis.ru
Lecture No. 1 Classification, structure of automated
electric drives (AED)
2) The structure of an automated electric drive (AED)
3) Efficiency of AED
4) Advantages of AEP
1 Classification of electric drives
AT Depending on the functions performed, the type and number of adjustable coordinates, the degree of automation of technological processes, the implementation of ES can be very different (Figure 1).
Manual
automated
Open Closed
Figure 1 - EP classification
Non-automated ES- control with the help of an operator who starts, stops, changes speed, reverses the electric drive in accordance with a given technological cycle.
Automated EP- control operations are performed in accordance with the requirements of the technological process. Operations are performed by the control system (the functions of turning on and off the EA are assigned to the operator). It is obvious that an automated electronic signature is more efficient and cost-effective, because frees a person from tedious and monotonous work, increases labor productivity, the quality of the technological process.
Open-loop EA - is characterized by the fact that all external influences (for example, the moment of inertia) affect its input coordinate, for example, speed. This type of EA is simple and is mainly used for starting, braking and reversing engines.
Closed EA - a distinctive feature is the complete or partial elimination of the influence of external influences on the controlled coordinate, such as speed. Patterns are usually complex.
Disturbance control- an additional signal proportional to the disturbance is fed to the input of the EA along with the reference signal, as a result, the total signal provides control of the EA. This regulation has not found proper application due to the complexity of the implementation of disturbing sensors, in particular, the load moment - Ms
Deviation control (feedback principle)- characterized by the presence of feedback circuits. Information about the controlled coordinate is fed to the input of the EA in the form of a feedback signal, which is compared with the master signal and the resulting signal (mismatch, shutdown, error) is the control signal for the EA (Fig. 2). Feedbacks can be positive and negative, linear and non-linear, rigid and flexible, etc.
K os |
||||
Figure 2-Closed structures of AED with compensation for perturbation (a), with feedback (b)
Positive feedback is such a feedback, the signal of which is directed according to (i.e., adds up) with the master signal.
Negative OS- OS signal is directed opposite to the setting signal. Rigid OS - operates both in steady state and in transient mode
Flexible OS - works only in transitional modes.
Linear feedback - is characterized by a proportional relationship between the controlled coordinate and the feedback signal.
Nonlinear OS - this dependence is not linear.
2 Structure of AEP
An automated electric drive is an electromechanical system that generally consists of an electric motor, converter, transmission and control devices and is designed to set in motion the executive bodies of working machines and control this movement (Figure 3).
Source of electrical energy (IEE)
Converter device
Ud ,Id ,fd
manager |
Electric motor |
|||||||
device (UU) |
body device |
|||||||
Md , ωd |
Fd , Vd |
|||||||
reverse |
gear |
|||||||
device (PRD) |
||||||||
Mm (Fm), ωm (Vm)
Consumer of mechanical energy (PME)
Figure 3 - Structural diagram of AED
The main purpose of AEP is the conversion of electricity into mechanical energy of the executive bodies of machines and mechanisms. In some cases (generator mode, braking), the reverse transformation is also possible.
AES accounts for 60% of the electricity generated in the country.
Figure 3 shows:
electrical energy flows - , mechanical energy flows - ;
PRB - convert electric energy into the required form (magnetic starters, thyristor switches, regulators, converters, etc.);
PRD convert mechanical energy into the required form for the consumer of mechanical energy (PME) (couplings, pulley-belt drives, gearboxes, etc.);
CU - information part (microprocessor means, microcomputer).
3 AED efficiency
As with any electromechanical device, an important indicator is the efficiency
AEP \u003d PRB ED PD,
because the efficiency of the PRB and PRD ≈1 and depends little on the load, then the AEF is determined by the ED, which is also quite high and at the rated load is 60-95%.
Low efficiency corresponds to low-speed engines of low power
With an increase in power above 1 kW, the ED and, accordingly, the AEF exceeds 70%.
4 Advantages of AEP
1) low noise level during operation;
2) lack of environmental pollution;
3) wide range of powers and angular speeds of rotation;
4) stabilization of the output coordinate;
5) the availability of regulation of the angular velocity of rotation and, accordingly, the performance of the process unit; 6) the relative ease of automation, installation, operation in comparison
nenie with heat engines, for example, internal combustion, as well as hydraulic and pneumatic drives.
Lecture 2 Adjusting the coordinates of the EP
1) EP speed control indicators
2) Regulation of torque, current, position of EA
3) Ways to control the speed of the DPT
4) Methods for regulating the speed of rotation of blood pressure
1 Indicators of EP speed control
To ensure the required modes of operation of machines, production mechanisms and the ED itself, some variables that characterize their operation must be regulated. Such variables, often called coordinates in EA, are, for example, speed, acceleration, position of the executive body (EO) or any other mechanical element of the drive, currents in the electrical circuits of motors, moments on their shaft, etc.
A typical example of the need to control the coordinates is the EP of a passenger elevator. When starting and stopping the elevator car, to ensure the comfort of passengers, the acceleration and deceleration of its movement are limited. Before stopping, the cabin speed must be reduced, i.e. regulated. And, finally, the cabin with a given accuracy must stop at the required floor. Such control of the movement of the elevator car is provided by adjusting the corresponding coordinates (variables) of the elevator EP.
The process of adjusting the coordinates is always associated with obtaining artificial (adjusting) characteristics of the engine, which is achieved by purposefully influencing the engine.
EP speed control.
The regulation of the speed of movement of the executive bodies is required in many working machines and mechanisms - rolling mills, hoisting and transport mechanisms, mining and paper machines, metalworking machines, etc. With the help of the EA, the regulation and stabilization of the speed of movement of their EO, as well as changing the speed of the EO are provided. in accordance with an arbitrarily changing reference signal (tracking) or according to a predetermined program (program movement). Let us consider how, with the help of an ED, it is possible to ensure the regulation of the speed of the IO of working machines.
As follows from the general scheme of the EP (lecture 1), the speed of the engine and the IO during its rotational (translational) movement are interconnected by the relations
Analysis of the expression shows that it is possible to control the speed of the RO by acting either on the mechanical transmission (i is the gear ratio of the gearbox), or on the engine, or on both at the same time.
In the first case, the effect is to change the gear ratio or the reduction radius of the mechanical transmission at a constant engine speed, so this method of regulation is called mechanical. For its implementation, gearboxes (with step regulation), variators and electromagnetic clutches (for smooth regulation) are used. The mechanical method is used to a limited extent due to the complexity of automating such technological processes, a small set of adjustable mechanical gears of this type and their low reliability and efficiency.
The IO speed control method, called electric, provides for the impact on the engine with unchanged mechanical transmission parameters. This method has found wide application in modern EP due to its large adjustment capabilities, simplicity, ease of use in the general scheme of automation of technological processes and economy.
The combined method of controlling the speed of IE is used to a limited extent mainly in the EP of metalworking machines.
So, the control of the movement of the executive bodies of modern working machines and mechanisms in most cases is achieved through a targeted impact on the electric motor using its control system in order to obtain the appropriate artificial characteristics.
For example, Figure 1 shows the natural mechanical characteristic 1 of a DC motor of independent excitation (DPT NV) and two artificial ones - when an additional resistor with resistance is introduced into the armature circuit (straight line 2) and the voltage supplied to the armature is reduced (straight line 3). Both of these artificial characteristics provide, at a load moment Ms, a reduction in speed to the required level. An increase in the speed of the DPTNV above the nominal value can be obtained by reducing its magnetic flux.
The following indicators are used to quantify and compare different speed control methods.
Speed control range , defined by the ratio
maximum speed to minimum, i.e. Dmax. Lower limit,
usually limited by overload capacity and rigidity characteristics.
In accordance with Figure 1, the control range will be determined by the ratio of rotational speeds at a given load torque Ms.
MS
ω nom
ω and
Figure 1 - Variants of speed control DPT NV
Speed stability, characterized by a change in speed with possible fluctuations in the load moment on the motor shaft and determined by the rigidity of its mechanical characteristics. The larger it is, the more stable the speed is with changes in the load moment, and vice versa. In this example, greater stability is provided with an artificial characteristic of 3.
Smoothness of speed control , determined by the speed difference
growth during the transition from one artificial characteristic to another. The more artificial characteristics can be obtained in a given range of speed control, the smoother the speed control will be.
Speed regulation direction . Depending on the method of influence on the engine and the type of artificial characteristics obtained, its speed may increase or decrease in comparison with operation on a natural characteristic at a given load moment. In the first case, they talk about speed control up from the main characteristic, in the second - down. It can be said that upward speed control is associated with obtaining artificial mechanical characteristics that are higher than natural, and downward speed control is provided by characteristics that are lower than natural.
Permissible engine load . An electric motor is calculated and designed in such a way that, while operating on a natural characteristic with rated speed, current, torque and power, it does not heat up above a certain temperature for which its insulation is designed. In this case, its service life is standard and is usually 15 ... 20 years.
Since the energy loss during heating of the motor is proportional to the square of the current, the standard heating will take place during the flow of
transcript
1 A.V. Romanov ELECTRIC DRIVE Course of lectures Voronezh 006 0
2 Voronezh State Technical University A.V. Romanov ELECTRIC DRIVE Approved by the Editorial and Publishing Council of the University as a textbook Voronezh 006 1
3 UDC 6-83(075.8) Romanov A.V. Electric drive: Course of lectures. Voronezh: Voronezh. state tech. un-t, s. The course of lectures deals with the issues of construction of electric drives of direct and alternating current, analysis of electromechanical and mechanical characteristics of electric machines, principles of control in an electric drive. The publication complies with the requirements of the State Educational Standard of Higher Professional Education in the direction of "Electrical Engineering, Electromechanics and Electrotechnology". The course of lectures is intended for second-year students of the specialty "Electric Drive and Automation of Industrial Installations and Technological Complexes" of full-time education on the basis of secondary vocational education. The publication is intended for students of technical specialties, graduate students and specialists involved in the development of electric drives. Tab. 3. Ill. 7. Bibliography: 6 titles. Scientific editor tech. sciences, prof. Yu.M. Frolov Reviewers: Department of Automation of Technological Processes, Voronezh State University of Architecture and Civil Engineering (Head of the Department, Doctor of Engineering Sciences, Prof. VD Volkov); Dr. tech. sciences, prof. A.I. Shiyanov Romanov A.V., 006 Design. GOUVPO "Voronezh State Technical University", 006
4 INTRODUCTION The electric drive (ED) plays an important role in the implementation of the tasks of increasing labor productivity in various sectors of the national economy, automation and complex mechanization of production processes. About 70% of the generated electricity is converted into mechanical energy by electric motors (EM), which set in motion various machines and mechanisms. A modern electric drive is distinguished by a wide variety of control means used from conventional switching equipment to computers, a large range of motor power, a speed control range of up to 10,000: 1 or more, and the use of both low-speed and ultra-high-speed electric motors. An electric drive is a single electromechanical system, the electrical part of which consists of an electric motor, converter, control and information devices, and the mechanical part includes all the associated moving masses of the drive and mechanism. The widespread introduction of electric drive in all industries and the ever-increasing requirements for the static and dynamic characteristics of electric drives place increased demands on the professional training of specialists in the field of electric drive. It should be noted that since full-time students on the basis of secondary specialized education are given a minimum number of study hours for mastering a specialty by the curriculum, progress in professional knowledge is highly dependent on the independent work of students. In particular, at the end of this edition there is a bibliographic list of scientific and technical literature recommended for study in addition to the proposed lecture notes. In addition, in addition to the course of lectures, a laboratory workshop on electric drive was released, which addresses the issues of experimental research 3
5 electric drives of direct and alternating current. For a more successful assimilation of the discipline, students are recommended to study the text of lectures and the content of laboratory work in advance. The State Educational Standard of Higher Professional Education of the Russian Federation regulates the following mandatory topics for the training course in the discipline "Electric Drive". EXTRACT from the State educational standard of higher professional education of state requirements for the minimum content and level of training of a certified engineer in the direction of "Electrical Engineering, Electromechanics and Electrotechnology", specializing in "Electric Drive and Automation of Industrial Installations and Technological Complexes" OPD.F. 09. "Electric drive" Electric drive as a system; block diagram of the electric drive; mechanical part of the power channel of the electric drive; physical processes in electric drives with DC machines, asynchronous and synchronous machines; electrical part of the power channel of the electric drive; principles of control in the electric drive; element base of the information channel; synthesis of structures and parameters of the information channel; design elements of the electric drive. The material of this course of lectures is fully consistent with this topic. four
6 LECTURE 1 HISTORY OF THE DEVELOPMENT OF THE ELECTRIC DRIVE AS A BRANCH OF SCIENCE AND TECHNOLOGY Issues addressed in the lecture. 1. Brief historical background on the development of AC and DC electric drives. Works of domestic and foreign scientists. 3. The role of the electric drive in the national economy. 4. Structure and main elements of a modern automated electric drive. The electric drive is a relatively young branch of science and technology, with a little more than a century since its practical application. The emergence of EP is due to the work of many domestic and foreign scientists in electrical engineering. This brilliant series includes the names of such prominent scientists as the Dane H. Erested, who showed the possibility of interaction between a magnetic field and a conductor with current (180), the Frenchman A. Ampère, who mathematically formalized this interaction in the same 180, the Englishman M. Faraday, built in 181 an experimental installation that proved the possibility of building an electric motor. These are domestic academicians B.S. Jacobi and E.H. Lenz, who first managed to create a direct current electric motor in 1834. The work of B.S. Jacobi on the creation of the engine gained wide world fame, and many subsequent works in this area were a variation or development of his ideas, for example, in 1837 the American Davenport built his electric motor with a simpler commutator. In 1838 B.S. Jacobi improved the design of the ED, introducing into it almost all the elements of a modern electric machine. This electric motor, with a power of 1 hp, was used to drive a boat, which, with 1 passengers, moved at a speed of up to 5 km / h against the He-5 current.
7 you. Therefore, 1838 is considered the year of birth of the electric drive. Already on this first, still imperfect model of the electric drive, its very significant advantages were revealed in comparison with the steam mechanisms that prevailed at that time - this is the absence of a steam boiler, fuel and water supplies, i.e. significantly better weight and size indicators. However, the imperfection of the first ED, and most importantly, the uneconomical source of electricity of the galvanic battery, which was developed by the Italian L. Galvani (), were the reason that the work of B.S. Jacobi and his followers did not immediately receive practical application. A simple, reliable and economical source of electrical energy was required. And the way out was found. Back in 1833, Academician E.Kh. Lenz discovered the principle of reversibility of electrical machines, which later combined the development of engines and generators. And in 1870, an employee of the French company "Alliance" Z. Gramm created an industrial type of DC electric generator, which gave a new impetus to the development of the electric drive and its introduction into industry. Here are some examples. Our compatriot electrical engineer V.N. Chikolev () creates in 1879 an EP for arc lamps, electric drives for a sewing machine (188) and a fan (1886), awarded gold medals at all-Russian exhibitions. There is an introduction of direct current electric current in the navy: an ammunition lift on the battleship "Sisoi the Great" (), the first steering gear on the battleship "1 Apostles" (199). In 1895 A.V. Shubin developed the "injector-engine" system for steering, which was later installed on the battleships "Prince Suvorov", "Slava" and others. a significant number of DC motors. 6
8 There are cases of using an electric drive in urban transport, tram lines in the cities of Kyiv, Kazan and Nizhny Novgorod (189) and somewhat later in Moscow (1903) and St. Petersburg (1907). However, the reported successes have been modest. In 1890, the electric drive accounted for only 5% of the total power of the mechanisms used. The emerging practical experience required analysis, systematization and development of a theoretical framework for subsequent coverage of the development of EP. A huge role here was played by the scientific work of our compatriot, the largest electrical engineer D.A. Lachinov (), published in 1880 in the journal "Electricity" under the title "Electromechanical work", which laid the first foundations of the science of electric drive. YES. Lachinov convincingly proved the advantages of the electrical distribution of mechanical energy, for the first time gave an expression for the mechanical characteristics of a DC motor with series excitation, gave a classification of electrical machines according to the method of excitation, and considered the conditions for supplying the engine from a generator. Therefore, 1880, the year of the publication of the scientific work "Electromechanical Work", is considered the year of the birth of the science of electric drive. Along with the DC electric drive, make your way into life and the AC drive. In 1841, the Englishman C. Whitson built a single-phase synchronous electric motor. But he did not find practical application due to difficulties during launch. In 1876, P.N. Yablochkov () developed several designs of synchronous generators to power the candles he invented, and also invented a transformer. The next step on the way to AC EP was the discovery in 1888 by the Italian G. Ferraris and the Yugoslav N. Tesla of the phenomenon of a rotating magnetic field, which marked the beginning of the design of multi-phase electric motors. Ferraris and Tesla 7
9, several models of two-phase AC motors have been developed. However, two-phase current in Europe is not widely used. The reason for this was the development by the Russian electrical engineer M.O. Dolivo-Dobrovolsky () in 1889 for a more advanced three-phase alternating current system. In the same year, 1889, on March 8, he patented an asynchronous electric motor with a squirrel-cage rotor (AD short circuit), and somewhat later with a phase rotor. Already in 1891, at the electrical exhibition in Frankfurt am Main, M.O. Dolivo-Dobrovolsky demonstrated asynchronous electric motors with a power of 0.1 kW (fan); 1.5 kW (DC generator) and 75 kW (pump). Dolivo-Dobrovolsky also developed a 3-phase synchronous generator and a 3-phase transformer, the design of which remains practically unchanged in our time. Marcel Despres in 1881 substantiated the possibility of transmitting electricity at a distance, and in 188 the first transmission line was built with a length of 57 km and a power of 3 kW. As a result of the above works, the last fundamental technical obstacles to the spread of electrical energy transmission were eliminated and the most reliable, simple and cheap electric motor was created, which is currently enjoying exceptional distribution. More than 50% of all electricity is converted into mechanical power by means of the most massive electric drive based on short circuit AD. The first 3-phase AC EP in Russia were installed in 1893 in Shepetovka and at the Kolomensky plant, where by 1895 09 electric motors with a total capacity of 1507 kW were installed. And yet, the pace of introduction of the electric drive into the industry remained low due to the backwardness of Russia in the field of electrical production 8
10 (.5% of world production) and electricity generation (15th place in the world) even during the heyday of tsarist Russia (1913). After the victory of the Great October Revolution in 190, the question of a radical reorganization of the entire national economy was raised. The GOELRO plan (the state plan for the electrification of Russia) was developed, which provides for the creation of 30 thermal and hydroelectric power plants with a total capacity of 1 million 750 thousand kW (by 1935, about 4.5 million kW were commissioned). Working on the GOELRO plan, V.I. Lenin noted that "the electric drive just most reliably ensures any speed and automatic connection of operations in the most extensive field of labor." Why was so much attention paid to electric drive and electrification? The point is obvious that the electric drive is the power basis for performing mechanical work and automating production processes with high efficiency, while the electric drive creates all the conditions for highly productive work. Here is a simple example. It is known that during the working day one person can generate about 1 kW / h with the help of muscular energy, the cost of production of which is (conditionally) 1 kopeck. In highly electrified industries, the installed power of electric motors per worker is 4-5 kW (this indicator is called the electric power of labor). With an eight-hour working day, we get a consumption of 3-40 kW / h. This means that the worker controls the mechanisms, the work of which per shift is equivalent to the work of 3-40 people. Even greater efficiency of EP is observed in the mining industry. For example, on a walking excavator of the ESH-15/15 type, having an arrow of 15 meters and a bucket with a capacity of 15 cubic meters, the power of one asynchronous motor is 8 MW. At rolling mills 9
11 The installed power of ED is more than 60 MW, and the rolling speed is 16 km/h. That is why it was so important to ensure the widespread introduction of the electric drive in the national economy. Quantitatively, this is characterized by an electrification coefficient equal to the ratio of the power of electric motors to the power of all installed motors, including non-electric ones. The dynamics of the growth of the electrification coefficient in Russia can be traced in Table 1.1. The value of the electrification coefficient, % per year, about leading world powers. At present, EP has taken a dominant position in the national economy and consumes about one-third of the total electrical energy produced in the country (about 1.5 trillion kW/h). So what is an electric drive? According to GOST R, an electric drive is an electromechanical system consisting, in the general case, of interacting power converters, electromechanical and mechanical converters, control and information devices and interface devices with external electrical, mechanical, control and information systems, designed to set in motion executive bodies (IO ) working machine 10
12 Electrical network Converter device Electric motor device Control information device Transmission device Working machine Executive body electrical connection mechanical connection This definition is illustrated in Fig. Let's decipher the components. A converting device (electricity converter) is an electrical device that converts electrical energy with one parameter values and/or quality indicators into electrical energy with other parameter values and/or quality indicators. (Note that the parameters can be converted according to the type of current, voltage, frequency, number of phases, voltage phase, according to GOST 18311). Converters are classified by current (direct and alternating current), as well as by the elemental base of thyristor and transistor converters. eleven
13 Electric motor device (electromechanical converter) is an electrical device designed to convert electrical energy into mechanical energy or mechanical energy into electrical energy. The electric motors used in the electric drive can be of alternating and direct current. By power, electrical machines can be conditionally divided into: micromachines up to 0.6 kW. low power machines up to 100 kW. medium power machines up to 1000 kW. high power over 1000 kW. By rotation speed: low-speed up to 500 rpm. medium speed up to 1500 rpm. high-speed up to 3000 rpm. ultra-high-speed up to rpm. According to the rated voltage, there are low-voltage motors (up to 1000 V) and high-voltage motors (above 1000 V). Control information device. The control device is designed to generate control actions in the electric drive and is a set of functionally interconnected electromagnetic, electromechanical, semiconductor elements. In the simplest case, the control device can be reduced to a conventional switch that turns on the ED in the network. High-precision ED contain microprocessors and computers in the control device. The information device is intended for receiving, converting, storing, distributing and issuing information about the variables of the electric drive, the technological process and related systems for use in the electric drive control system and external information systems. The transmission device consists of a mechanical transmission and an interface device. A mechanical transmission is a mechanical converter designed to transmit 1
14 chi mechanical energy from ED to the executive body of the working machine and the coordination of the type and speed of their movement. The interface device is a set of electrical and mechanical elements that ensure the interaction of the electric drive with adjacent systems and individual parts of the electric drive with each other. Reducers, V-belt and chain drives, electromagnetic slip clutches, etc. can act as a transmission device. A working machine is a machine that changes the shape, properties, state and position of the object of labor. The executive body of a working machine is a moving element of a working machine that performs a technological operation. These definitions need to be supplemented. The electric drive control system is a set of control and information devices and ED interface devices designed to control the electromechanical energy conversion in order to ensure the specified movement of the working machine's executive body. The control system of the electric drive is a higher-level control system external to the electric drive that supplies the information necessary for the functioning of the electric drive. 13
15 LECTURE ELECTRIC DRIVE THE MAIN ELEMENT OF INTEGRATED MECHANIZATION AND AUTOMATION OF TECHNOLOGICAL PROCESSES IN MACHINE PRODUCTION Issues discussed in the lecture. 1. Structural evolution of electric drives. Various types of electric drives used in industry and agriculture. 3. The main trends in the development of electric drives. 4. The structure of the EP from the standpoint of the "Theory of the electric drive". Over the years of its existence, the electric drive has undergone fundamental changes. First of all, methods of transferring mechanical energy from engines to working machines were improved. For example, in our country, before the beginning of the first five-year plan (198), a group electric drive "an electric drive with one electric motor that ensures the movement of the executive bodies of several working machines or several IO of one working machine" dominated, but by the end of the first five-year plan (193) it was withdrawn from industry . Fig..1 shows a functional diagram of a group electric drive of an enterprise. The peculiarity of this scheme is in the mechanical distribution of energy throughout the enterprise and, accordingly, in the mechanical control of the process, i.e. management of the work of the executive bodies of working machines. Figure .. shows another diagram of a group electric drive of a group electric drive of working machines. Unlike the previous scheme, the electrical energy here is supplied directly to the RM, and already in them it is mechanically distributed. The mechanical control of the work is preserved. Among the common disadvantages of a group electric drive are: step speed control; fourteen
16 Electrical network U, I electrical energy EM transmission shaft M, ω mechanical energy RM 1 RM IO 1 IO 3 IO 1 IO 3 Fig..1. Group electric drive of the enterprise Electric network ED 1 ED RM 1 RM IO 1 IO 3 IO 1 IO 3 Fig... Group electric drive of working machines small control range; dangerous working conditions; low performance. The group electric drive was replaced by a more promising and economical individual electric drive, this is "EP, providing the movement of one executive body of the working machine", the functional diagram is shown 15
17 in Fig..3. In this version of the electric drive, the distribution of electrical energy occurs up to the working bodies. It also becomes possible to control mechanical energy electrically. In addition, an individual drive makes it possible in some cases to simplify the design of the RM, since ED is often structurally a working body (fan, electric drill, etc.). Electrical network RM ED 1 ED ED 3 IO 1 IO IO 3 Fig..3. Individual electric drive At present, an individual electric drive is the main type of industrially used electric drive. But not the only one. In a number of production mechanisms, an interconnected electric drive is used - these are "two or more electrically or mechanically interconnected electric drives, during operation of which a given ratio of their speeds and (or) loads and (or) the position of the executive bodies of working machines" is maintained. This type of electric drive combines two types of electric drives - a multi-motor electric drive and an electric shaft. Multi-motor electric drive (Fig..4) "an electric drive containing several electric motors, the mechanical connection between which is carried out through the executive body of the working machine" . In a number of cases, such an electric drive makes it possible to reduce the forces in the working body, distribute them more evenly and without distortions in the mechanism, and increase the reliability and productivity of the installation. 16
18 Electrical network ED 1 RM ED Fig..4. Multi-motor electric drive A multi-motor electric drive is used in mine hoists, in particular, it was first used in Shepetovka at the end of the 19th century. Electric shaft "an interconnected electric drive that provides synchronous movement of two or more executive bodies of a working machine that do not have a mechanical connection" . Examples include sluice drives and long conveyor lines. Fig..5 shows a diagram of a conveyor on asynchronous EM with a phase rotor, explaining the principle of operation of an electric shaft. The rotational speeds ω 1 and ω, due to the electrical connection of the rotors of the electric motors, will be the same or synchronous. ω 1 conveyor belt ω EM 1 EM electric shaft Fig..5. Illustration of the electric shaft operation
19 EM power range from fractions of a watt to kW, speed control range up to 10,000:1 or more, using both low-speed motors (hundreds of rpm) and high-speed ones (up to rpm). EP is the basis for automation of technological objects in industry, agriculture, space; realizing the most important task of our time, increasing labor productivity. Currently, the electric drive is characterized by a tendency to use energy-saving technologies. To traditional systems that allow energy to be returned to the network (this process is called recuperation), such as a generator-motor system (G-D system), an electric cascade (an adjustable electric drive with a IM with a phase rotor, in which slip energy is returned to the electric network), electromechanical cascade (adjustable electric drive with IM with a phase rotor, in which the slip energy is converted into mechanical energy and transferred to the EM shaft), there is a mass replacement of an unregulated electric drive with an adjustable one. As a consequence, the design of the EA becomes gearless, which increases the overall efficiency of the drive. Progress in the design of converter technology, in particular for frequency converters, stimulates the replacement of DC motors and synchronous EMs with cheaper and more reliable asynchronous EMs with a squirrel-cage rotor. If we consider electric propulsion systems from the standpoint of the theory of electric drive, then as an object of study it is an electromechanical system, which is a set of mechanical and electromechanical devices united by common power electrical circuits and (or) control circuits, designed to implement the mechanical movement of the object. In the electric drive, three parts are combined into a single whole (Fig. 6): the mechanical part, the electric motor and the control system. eighteen
20 Email network Email engine M, ω Mech. part Useful mechanical work ECS EMP RD PU IM DOS M mech to DOS ISU from DOS Control system from memory Fig..6. Functional diagram of the electric drive from the point of view of the theory of the electric drive The mechanical part includes all moving elements of the mechanism of the RD motor rotor, the PU transmission device, the IM actuator, to which the useful mechanical moment M mech is transmitted. The electric motor device includes: an electromechanical energy converter EMF, which converts electrical power into mechanical power, and the rotor of the RD engine, which is affected by the electromagnetic torque M of the engine at a rotation frequency (angular velocity) ω. The control system (CS) includes the energy part of the ECS and the information part of the IMS. The ISU receives signals from the master devices of the memory and feedback sensors DOC. 19
21 LECTURE 3 MECHANICAL PART OF THE ELECTRIC DRIVE Issues discussed in the lecture. 1. Purpose and main mechanical components of the EP. Active and reactive static moments. 3. Typical loads of the mechanical part of the electric drive. The main function of the electric drive is to set the working machine in motion in accordance with the requirements of the technological regime. This movement is performed by the mechanical part of the electric drive (MCH EP), which includes the rotor of the electric motor, the transmission device and the working machine (Fig. 3.1). Shown in fig. 3.1 parameters denote M in, M rm, M io moments on the shaft of the engine, working machine, executive body; ω in, ω rm, ω io angular velocities of the EM shaft, working machine, executive body; F io, V io force and linear speed of the executive body. Rotor M in ω in Transfer device M rm ω rm Working machine M io ω io F io V io Fig.3.1. Scheme of the mechanical part of the electric drive Depending on the type of transmission and the designs of the working machine, they distinguish (Fig. 3.1): EP of rotational movement, which provides, respectively, the rotational movement of the executive body RM; output parameters moment IO mechanism M io and angular frequency of rotation ω io; EP of translational motion, which provides translational linear motion of the IO of the working machine; output parameters force F io and linear speed V io.
22 Note that there is also a special ED, called an oscillatory electric drive, which provides reciprocating (vibratory) movement (both angular and linear) of the RM executive body. In the mechanical part of the EP, there are various types of forces, moments, which differ in the nature of the action. Specifically, static moments are reactive M cf and active M ca. Reactive moments are created by the force of friction, the forces of compression, tension, torsion of inelastic bodies. A classic example here is dry friction (Fig. 3.). The friction forces always oppose the movement, and when the electric drive is reversed, the friction moment due to these forces also changes direction, and the function M c (ω) at a speed ω = 0 undergoes a discontinuity. Friction forces are manifested in the gears of the electric motor and working machines. F m V F tr ω F tr V m F M sr M sr M s 3.. Dependence of the static moment of dry friction forces on the speed Active (potential) moments are created by gravity, compression, tension, torsion forces of elastic bodies. In MCH EA, active moments arise in loaded elements (shafts, gears, etc.) during their deformation, since mechanical connections are not absolutely rigid. The features of the action of potential moments are clearly manifested by the example of gravity. When lifting or 1
23 when the load is lowered, the direction of gravity F j remains constant. In other words, when the electric drive is reversed, the direction of the active moment M sa remains unchanged (Fig. 3.3). ω M s V V M sa keeps it constant. Working machines, despite the great variety of designs and operations performed, can be classified according to the type of dependence of the static moment on a number of factors. There are 5 groups of mechanisms on an enlarged basis. The first group includes mechanisms in which the static moment does not depend on the rotation speed, that is, M c (ω) = const. This means that the mechanical characteristic of the working machine, the dependence of the static moment on the rotational speed is a straight line parallel to the axis of the angular velocity ω, and undergoes a discontinuity at ω = 0 for reactive static moments (as shown in Fig. 3.), For example, for a belt conveyor with uniform linear load. F j m
24 For active Ms (as shown in Fig. 3.3) the mechanical characteristic is independent of the direction of motion. A typical example is the lift mechanism. The second group of mechanisms is quite representative [, 3]. Here, M c depends on the speed of rotation of the RM: () = M + (M + M) Ms c0 sn c0 a ω ωn ω, (3.1) where M from the moment of mechanical friction losses; M SN static moment of the working machine at the rated speed ω n; ω current rotation speed; and the proportionality factor. At a = 0, we have M c (ω) = M cn, that is, we obtain the mechanical characteristic of the machines of the first group. With a = 1, we have a linear dependence of the static torque on the speed, which is inherent, for example, in DC generators G operating at a constant resistance R (Fig. 3.4). ~ U 1, f 1 G R ω M s (ω) U ov OV M s0 M s fans, propellers, centrifugal pumps, and other such mechanisms). 3
25 ~ U 1, f 1 ω М с (ω) М с0 reduces the processing speed of the part ω (Fig. 3.6). М с ~ U 1, f 1 ω V ω М с (ω) The third group of mechanisms is a group of machines in which the static moment is a function of the angle of rotation of the shaft PM α, that is, M c = f(α). This is typical, for example, of connecting rod-crank (Figure 3.7) and eccentric mechanisms, in which the rotational movement with a rotation frequency ω is converted into a reciprocating movement with a speed V. The working stroke of the mechanism, at which 4 M s0 M s is reached
26 is the maximum static moment M cmax, there is, for example, at 0 α π, a reverse motion with a maximum moment at π α π. M cmax, хх ω М s M cmax М s (α) M cmax, хх V М s on the speed of movement, i.e. М с = f(α, ω) A similar dependence is observed when electric transport moves on a rounded section of the track. The fifth group of mechanisms is the RM group, in which the static moment changes randomly in time. It includes geological drilling rigs, coarse crushers and other similar mechanisms (Fig. 3.8). α М с ω М с (t) 0 t
27 LECTURE 4 DC ELECTRIC MACHINES Questions discussed in the lecture. 1. The design of DC machines .. Basic parameters and electromechanical energy conversion in DC machines. 3. Classification of DC motors. 4. Approximate determination of armature resistance. The DC electric machine (MPT) has a specific design. Schematically, using the P-9 electric motor as an example, it is shown in Fig. The fixed part (stator) contains the main poles 1 with coils that form an inductor or excitation system of the machine. The poles are evenly distributed on the inner surface of the frame 3, which combines the functions of the mechanical part (housing) and the active part (yoke of the stator magnetic circuit). Since a constant magnetic flux passes through the frame (yoke), which does not induce eddy currents in it, it is made of monolithic steel. The cores of the main poles are most often made laminated: they consist of individual plates tied together with rivets, studs, or others. Such a design solution is not used to limit eddy currents, but rather is dictated by the convenience of manufacturing the pole. In addition to the excitation windings (OB), the main poles of the MPT can contain a compensation winding designed to compensate for the demagnetizing effect of the armature's own magnetic field (armature reaction), as well as a stabilizing winding used for low-speed high-power motors when it is necessary to temporarily increase the speed by 5 times. To ensure sparkless switching, the machine is provided with additional poles 4, the windings of which are connected in series to the rotor circuit. 6
28 Fig. DC machine type P-9 The MPT rotor is more often called an armature. It carries the main winding of the machine, through which its main current flows. Anchor winding 5 is located in the grooves of the magnetic circuit 6. Conclusions 7
29 windings are connected to the collector plates 7. The magnetic circuit and the collector are placed on a common shaft 8. For normal operation of the DC machine, the grooves of the magnetic circuit must be strictly oriented relative to the plates 7. Collector brushes are pressed against the outer (active) surface of the collector. (coal, graphite, composite, etc.). One group may contain one or more brushes, depending on the current passed through the contact. The contact area is important (it is desirable to provide a fit close to 100%) and the force of pressing the brush to the collector. The brushes are mounted in brush holders that orient and press the brush. The brush holders themselves are placed on special pins of the traverse 9 mounted on the inner side of the bearing shield 10. The traverse can be rotated around the axis of the machine and fixed in any selected position, which allows, if necessary, to adjust the position of the brushes on the collector from the condition of minimal sparking in the brush contact. DC machines are more often used as motors, they have a high starting torque, the ability to widely adjust the speed, are easily reversed, have almost linear control characteristics, and are economical. These advantages of MPT often put them out of competition in drives requiring wide and precise adjustments. An important advantage of MPTs is also the possibility of their regulation by low-current excitation circuits. However, these machines are used only where it is impossible to find an equivalent replacement. This is due to the presence of a brush-collector assembly, which causes most of the shortcomings of the MPT: it increases the cost, reduces the service life, creates radio interference, acoustic noise. Sparking under the brushes accelerates wear on the brushes and commutator plates. Wear products cover the inner cavity 8
30 machine with a thin conductive layer, degrading the insulation of conductive circuits. The operation of the electric motor and DC generator is characterized by the following basic quantities: M is the electromagnetic moment developed by the electric motor, N m; M c the moment of resistance (load, static moment) created by the production mechanism, N m, is usually reduced to the motor shaft (reduction formulas are discussed in lecture 14); I I armature current of the electric motor, A; U voltage applied to the anchor chain, V; E electromotive force (EMF) of a DC machine (for an electric motor it is called counter-emf, since in an electric motor it is directed towards the voltage U and prevents the flow of current), V; F magnetic flux created in the electric motor when the excitation current flows through the OF, Wb; R I armature circuit resistance, Ohm; ω is the angular frequency (speed) of rotation of the EM armature, s -1 (instead of ω, the value n, rpm is often used), 60 ω n =. (4.1) π R motor power, W, distinguish between mechanical (useful) power on the shaft EM R mech and full (electrical) power R mech = M ω, (4.) R el = U I i; (4.3) η efficiency factor of the MPT, equal to the ratio of useful power to total; λ coefficient of overload capacity, distinguish between overload capacity for current λ I and torque λ M: 9
31 λ I \u003d I max / I n; λ M = M max / M n. The relationship between the parameters of the MPT is reflected in the following four formulas: dω M M = c dt J, (4.4) E = K Ф ω, (4.5) U E Ii =, R i (4.6) M = K Ф I i, (4.7) where J is the moment inertia of the electric drive system, kg m; dω/dt angular acceleration of the motor shaft, c -1 ; K is the design constant of the electric motor, pn N K =, (4.8) π a where pn is the number of pairs of main poles; N is the number of active armature conductors; a is the number of pairs of parallel armature branches. Formula (4.4) is a modified record of the basic equation of motion of the electric drive dω M Mc = J. (4.9) dt Note that the basic equation of motion is an analog of Newton's law a = F/m. The only difference is that for rotational motion, linear acceleration is replaced by angular acceleration ε = dω/dt, mass m is replaced by moment of inertia J, and force F is replaced by dynamic moment M dyn, equal to the difference between the moment of the electric motor M and the static moment M s. Formula (4.5) reflects the principle of operation of a DC generator based on the law of electromagnetic induction. In order for the EMF to appear, it is enough to rotate the armature with a certain speed ω in the magnetic flux F. 30
32 EMF E in the machine cannot be obtained if at least one of the quantities is missing: ω (the motor does not rotate) or Ф (the machine is not excited). Formula (4.6) shows that the current I i in the armature circuit flows in the motor under the action of the voltage U applied to the armature. The value of this current is limited by the counter-emf generated during the rotation of the electric motor and the total resistance of the armature circuit. Formula (4.7) actually illustrates the principle of operation of a direct current ED based on the law of interaction of current in a conductor and a magnetic field (Ampère's law). For the occurrence of a torque, it is necessary to create a magnetic flux F and pass the current I I through the armature winding. The above formulas describe all the main processes in a DC motor. MPT is distinguished by the way the winding of the main poles (excitation winding) is included in the electrical circuit. 1. DC machines with independent excitation. The essence of the term is that the electric circuit of the excitation winding (OV) is independent of the power circuit of the EM rotor. For generators, this is the practical only option for a circuit solution, because. the excitation circuit controls the operation of the MPT. Excitation in DC motors with independent excitation (DPT NV) can be performed on permanent magnets. DPT NV with traditional OF have two channels for controlling the rotor voltage and the voltage of the excitation winding. DPT NV are the most popular DC electric machines. Electric motors with parallel excitation (DPT PV). They are characterized by the inclusion of OB in parallel with the ED armature circuit. According to their characteristics, they are close to DPT NV. 3. ED with sequential excitation (DPT Seq.V). The stator winding is connected in series with the rotor winding, which causes the dependence of the magnetic flux on the current.
33 anchors (actually from the load). They have non-linear characteristics and are rarely used in practice. 4. Motors with mixed excitation are a compromise EM with series and parallel excitation. Accordingly, in the ED there are two OBs - parallel and serial. If the value of the resistance of the armature winding is unknown, then an approximate formula can be used. Assuming that half of the power losses are associated with losses in the armature winding copper, we write the formula M U n n η =. n ω I n n n n i; or me. (4.11) In In R U n I R 3
34 LECTURE 5 MECHANICAL AND ELECTROMECHANICAL CHARACTERISTICS OF THE INDEPENDENTLY EXCITED DC MOTOR Issues discussed in the lecture. 1. Natural electromechanical and mechanical characteristics of a DC motor of independent excitation (DPT NV) .. Rigidity of the static characteristic. 3. System of relative units. 4. Mechanical and electromechanical characteristics of DPT NV in relative units. Before proceeding to the consideration of the characteristics of the DPT NV, we give some definitions. The mechanical characteristics (MX) of the engine are the dependences of the steady-state speed on the torque n \u003d f 1 (M) or ω \u003d f (M). The electromechanical characteristics (EMC) of the engine are the dependences of the steady-state speed on the current n \u003d f 3 (I) or ω \u003d f 4 (I). Both MX and EMC can also be represented by inverse functions M = ϕ 1 (n) or I = ϕ 4 (ω). The characteristics are called natural if they are obtained under nominal power conditions (at nominal voltage and speed), nominal excitation and the absence of additional resistances in the armature circuit. Engine characteristics are called artificial when any of the factors listed above are changed. To derive the electromechanical and mechanical characteristics of a DC motor with independent (parallel) excitation, consider the simplest motor switching circuit (Fig. 5.1). 33
35 U + - I E DP KO R add I in OB R DV + U in - Fig Electrical circuit diagram of a DC motor of independent excitation DC mains voltage U c \u003d U is applied to the armature of the electric motor, which in steady state is balanced by EMF (E) motor and voltage drop in the armature circuit (I I R yats). U \u003d E + I R yat, (5.1) where R yat = R i + R add + R dp + R to the total resistance of the armature circuit, Ohm; R I armature winding resistance, Ohm; R additional additional resistance in the armature circuit, Ohm; R dp, R ko respectively, winding resistance of additional poles and compensation winding, Ohm. Insulation class Table 5.1 Operating temperature, С А 105 Е 10 В 130 F 155 Н 180 С node. Bringing the resistance of the windings in the armature circuit
36 to the operating temperature t, C, is carried out according to the following formula: R \u003d R (1 + α θ), (5.) ; α temperature coefficient, (C) -1, for copper 3 usually take α \u003d 4 10 (C) -1; θ is the difference between the operating temperature and t 0, C. The additional resistance in the brush-collector assembly can be taken into account as the ratio of the voltage drop at the brush-collector contact U w = V to the rated armature current. Substituting the value of E into equation (5.1) according to (4.5) and making the appropriate transformations with respect to the rotational speed ω, we obtain the electromechanical characteristic of the DC electric motor of independent (parallel) excitation U I R n U R n ω = = I n. (5.3) Kfn Kfn Kfn Having expressed the value of the armature current through the electromagnetic torque (4.7) and substituting the current value into equation (5.3), we find the mechanical characteristic of a DC motor with independent (parallel) excitation: U R ац ω = M. (5.4) KФ ( ) n KFn Analyzing equations (5.3) and (5.4), we see that mathematically these are the equations of a straight line crossing the velocity axis at the point ω 0. The value ω 0 = U / (K Fn) is called the ideal idle speed, and the ratios R R jac Ib = M = ω c (5.5) KF KF () 35
37 is called a static speed difference relative to ω 0, caused by the presence of a static moment on the motor shaft. The following formula is valid: ω = ω 0 - ω s. (5.6) To construct a natural mechanical characteristic (EMH), it is necessary to find two points. One of them is determined from the passport data of the engine for nominal values n n and M n: ω n = π n n /30 = 0.105 n n, M n = P n / ω n, where P n is the rated power of the engine, W; n n rated speed of EM, rpm. The second point corresponds to the ideal idle when I = 0; M = 0. It can be found from equation (5.3) when substituting the passport data of the engine: Un ω ω n 0 =. (5.7) Un In R I The construction of a natural electromechanical characteristic (EEMH) occurs in a similar way using the passport value of the rated current I n. The EMX can be constructed knowing ω 0 and the slope of the characteristic, which is a straight line. The slope value is determined by the derivative dm/dω = β s, called the static stiffness of the mechanical characteristic (KF) dm β s = =. (5.8) dω R jac In practice, the modulus of static stiffness β = β s is used. The value of β depends on the resistance of the anchor circuit and the excitation magnetic flux. In view of the above, the mechanical characteristic equation can be written as ω = ω 0 M / β. (5.9) 36
38 To compare electric motors different in power, current, torque, number of pole pairs allows the representation of the characteristics of EM in relative units. The system of relative units is quite often used in technical calculations and is based on taking some arbitrary value as the base one. The absolute values of the parameters of the same physical nature k i, referred to the base value of k bases, can be compared with each other. In relative units o k k i i =. (5.10) kbase To analyze the characteristics of a DC motor of independent excitation, we will take for the base values: U n rated voltage; I n rated motor current; M n rated motor torque; ω 0 ideal idle speed; F n nominal magnetic flux. The basic resistance value is usually defined as R base = U n / I n, (5.11) where R base has the following physical meaning - this is the resistance of the armature circuit, which limits the armature current to the nominal value in the inhibited state (ω = 0) and the applied nominal voltage. To express the electromechanical characteristic (5.3) in relative units, it is necessary to divide the right and left sides of the equation by the ideal idle speed ω 0 EEMH. As a result, we obtain the expression o o o U o R ац ω = I, (5.1) o o Ф Ф 37
39 ω where ω o o U o Ф o I o R ац = ; U = ; F = ; I = ; R jac =. ω 0 U n F n I n R base The equation of the mechanical characteristic in relative units can be obtained from equation (5.1) after substituting the expression I = into it, where M =. o o M o M o M F n The natural characteristics of the DPT NV in relative units will take the form: a) electromechanical b) mechanical o o o R yat ω = 1 I, (5.13) o o o ω = 1 M R yat. (5.14) o o with I R o yc M o o yc Static velocity difference ω = = R, o o whence it follows that I = M. Thus, in relative units, the natural mechanical and electromechanical characteristics coincide. When M \u003d M n and I \u003d I n, from equations (5.13) and (5.14) it can be seen that the static drop at rated load is equal to the resistance of the armature circuit in relative units, that is, o \u003d R o ωsn yat. The value of yc depends on the engine power and is within the limits of 0, 0.0 for DPT NV with power from 0.5 to 1000 kW. Knowing the relative resistance of the armature, it is easy to determine the short-circuit current in relative units I k \u003d o Ik I o o o Ik U R Yats n. R o =, in absolute units, this current is 38
40 LECTURE 6 SPEED CONTROL IN A DC MOTOR Questions discussed in the lecture. 1. Artificial electromechanical (IEMH) and mechanical (IMH) characteristics of DCT NV with a change in rotor resistance. Artificial electromechanical and mechanical characteristics of DCT NV with a change in magnetic flux. 3. Artificial electromechanical and mechanical characteristics of DPT NV when the supply voltage changes. Rheostatic speed control is carried out by introducing additional active resistance resistors into the armature circuit, i.e. R jac \u003d (R i + R ya) \u003d var for U \u003d U n, F \u003d F n,. As can be seen from the mechanical characteristic equation (5.4), when varying the value of the additional resistance Rdya in the armature circuit, the ideal idle speed ω 0 remains constant, only the modulus of static stiffness β changes, and with it the stiffness (steepness) of the characteristic (Fig. 6.1) . For example, with the introduction of an additional resistor with a resistance R dya \u003d R i, the static stiffness modulus of the artificial mechanical characteristic (IMC) β and is two times less than for the natural characteristic β e, i.e. β and = 0.5 β e. Accordingly, the static velocity drop ω = ω + ω = ω will double. not R in relative units, the rheostatic mechanical characteristic can be written o o o o o o o ω = 1 M R n = 1 M R n + R n
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Introduction In synchronous machines, the angular speed of rotation of the rotor, Ω = 2πn, is equal to the synchronous angular velocity of the field, Ω s = 2πn 1 (term 37, p.15). The fields of the stator and rotor in synchronous machines (as in all
3 Contents Preface...5 Introduction...7 I. Electromagnetic moment and electromagnetic force of electric machines of rotational and translational motion. 1. General expression for moment and force. 14 2.
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Asynchronous Machines An asynchronous machine is a machine in which, during operation, a rotating magnetic field is excited, but the rotor of which rotates asynchronously, i.e. at a speed different from that of the field. 1 Suggested by Russian
CONTENTS Foreword... 3 Chapter 1. Linear electric circuits of direct current... 4 1.1. DC electrical devices... 4 1.2. Elements of the DC electrical circuit ... 5 1.3.
9. DC MACHINES DC machines are reversible machines, i.e. they can operate both in generator mode and in engine mode. DC motors have advantages
Topic 13 Synchronous generators, motors Plan 1. The design of a synchronous generator 2. The principle of operation of a synchronous generator 3. The design of a synchronous motor 4. The principle of operation of a synchronous motor
CONTENT OF THE EDUCATIONAL DISCIPLINE LIST AND CONTENT OF SECTIONS (MODULES) OF THE DISCIPLINE p / n Discipline module Lectures, part-time 1 Introduction 0.25 2 Linear DC electrical circuits 0.5 3 Linear electrical circuits
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CONTENTS Foreword.................................................... 5 1. Calculation of the power of electric drives of metal-cutting machines 1.1. General information.............................. 7 1.2. Planing machines ...............................................
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TOPIC 1. DC ELECTRIC MACHINES Task 1. In accordance with your version of the task (Table 1, columns 2, 3, 4), draw a sketch of a cross-section of a two-pole DC machine and show
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