SU1508337A1 - A.c. electric drive - Google Patents

Abstract

The invention relates to electrical engineering and can be used to control the working bodies of machines and mechanisms for general industrial purposes. The aim of the invention is to reduce power losses while maintaining high speed. The AC drive contains an asynchronous motor 1 with a short-circuited rotor, unit 4 of the coordinate conversion. The inputs of the unit 4 are connected respectively to the outputs of the logic switch 12 of the active and reactive current setting signals and the output of the driver 3 of the reference signals associated with an asynchronous motor. The drive provides three modes of operation. The first mode of operation is characterized by a constant magnitude of the chain linking of the engine 1, equal to (0.3-0.5) Ψ _n , where _n is the nominal value of the linkage corresponding to saturation. In this mode, the torque is controlled by changing the signal U _Q (active component of the current) and keeping U _D (reactive component of the current) constant. The second mode of operation is characterized by a simultaneous change of the signals U _Q and U _D , their alignment, while ensuring a minimum of losses. The magnetic flux of the engine 1 in this mode changes to a value of ψ _H. In the third mode of operation, overload moments are obtained at a nominal value of flow equal to ψ _H. An increase in the moment to above the nominal value in this mode occurs due to an increase in the signal U _Q. 1 il.

Description

1508

The invention relates to electrical engineering, namely, alternating current electric drives with torque control on the shaft by forming a stator current, and can be used in control systems of rotational speed and angular displacement of the working parts of machines and mechanisms of general purpose.

The purpose of the invention is to reduce power losses in the electric drive while maintaining high speed.

The drawing shows a functional diagram of the proposed electric drive. .

: The electric drive contains an asynchronous motor 1 with a short-circuited rotor connected to the output of a controlled current source 2, a shaper of 3 reference signals associated with an asynchronous motor 1 with a short-circuited rotor and connected to the input for the reference signals of the coordinate conversion unit 4, the output of which is connected to the charging input of the controlled current source 2, the control signal adjuster 5, connected to the output for the dividend division block 6, the reactive current driver 7, the output of which is connected To the input for the divider unit 6 division. At the same time, the inputs for controlling the active and reactive currents of the coordinate conversion unit 4 are respectively connected with the output of the division unit 6 and with the output of the reactive current driver 7.

In addition, a square root extractor 8 from the signal module, a 9-digit decider, two multipliers 10 and 11 multiplications and a logical switch 12 of the active and reactive current signal, equipped with three inputs 13-15 and connected to the same inputs for controlling the coordinate conversion unit 4. At the same time, the output of the setpoint control signals 5 is connected to the combined root of the input of the square root extraction unit 8 of the signal module, the input of the signal signer 9 and the first input 13 of the active and reactive current setting signal switch 12, the second 14 and the third 15 inputs of which are connected respectively, to the output of the first multiplication unit 10 and to the output of the reactive current driver 7. The output of the 9 sign decider is connected to the first input of the second multiplication unit 11, the second input of which is combined with the input for the divisible division unit 6 and the input of the reactive current driver 7 and connected to the output of the square root extraction unit 8. The output of the second multiplication unit 11 is connected to the first input of the first multiplication unit 10, the second input of which is connected to the output of the unit 6

division.

The reactive current driver 7 is configured as a limiter for the rate of change of the signal. The logic switch 12 of the active and reactive current setting signals is equipped with four elements 2-2IL-2ILI 16-19, two comparison elements 20 and 21, a minimum reactive current setting device 22 and reactive saturation current setting device 23, the second and third inputs of the first element 2- 2 and 2 or 16 and the second and third inputs of the second element 2-2 and 2 or 17 are interconnected and connected to the output of the first comparison element 20. The second and third inputs of the third element 2-2I-21SHI 18 and the second and third inputs of the fourth element 2-2I-21SH11 19 are interconnected and connected to the output of the second element 21 of the comparison.

The output of the setpoint generator 22 of the minimum reactive current is connected to the first input of the second comparison element 21 and the fourth input of the fourth element 2-2 and 2IL 19 connected to each other. The output of the 23 setting generator of the reactive saturation current is connected to the first input of the first comparison element 20 combined with the fourth to the input of the second element 2-2I-2ShSh 17. The first input 13 of the logic switch 12 of the active and reactive current setting signals form the fourth inputs of the first 16 and third 18 elements 2-2I-2ILN interconnected. The second input 14 of the logic switch 12 forms the first input of the first element 2-2I-21SH 16. The third input 15 of the logic switch 12 forms the combined second inputs of the comparison elements 20 and 21 and the first input of the second element 2-2I-21SH 17. The outputs of the logic switch 12 active and reactive reference signals

currents form the outputs of the third 18 and fourth 19 elements 2-2Ii-21iJLi,

Each of elements 2-2И-2ШШ 16 - 19 contains two-input elements Н 24-31 and a two-input element Ш1И 32-35 connected to their outputs, formed on the basis of corresponding logic elements.

The drive operates in the following manner.

Torque control on the shaft of the induction motor 1 is provided by separate and independent

stator current components in static operation modes.

From the output of the setpoint control signals 5 (its role in the closed system is played, for example, by the speed controller), the signal U, is received. The transmission factors of the units mentioned below are equal to one.

At the output of the detector 9 s mm signal is obtained with. U,; 1 (:: -: number of a and equal to

and, 1 .SignU. (one)

At the output of the block 8 extraction core

The stator current components are quenched (a square signal from a newly rotating orthogonal coordinate system oriented along the rotor flux vector. The specified stator current components are controlled by the UB and UQ signals of the DC setting, and the U component determines the current component the stator, oriented along the flux coupling vector (called the conditionally reactive current component), and the signal UQ-determines the stator current component orthogonal in the leading direction vector rotor flux separation (called the normally active component of the current).

The control signals for the phase currents of the asynchronous motor 1 in the fixed coordinate system connected with the stator are generated using the coordinate conversion unit 4. The harmonic signals required for the coordinate transformations, which vary with the frequency of the rotating magnetic field of the induction motor 1, are generated using the shaper 3 reference signals. The shaper 3 of the reference signals can be built on the basis of an angular position sensor of the motor shaft and a separate slip determinant, as well as on the basis of flow sensors or EMF. Depending on its specific version, the signals Ujj and UQ of the reference can also be sent to the inputs of the imaging unit 3 of the reference signals (shown by dashes in the drawing).

In the AC drive, it is solved by setting the minimization of power losses in an asynchronous motor while adjusting the torque to the nominal, which is determined by maintaining the equality of the active and reactive

20

emit a signal equal to u

and 2)

Using the multiplication unit 10, a signal Uj equal to

, U, SignU.

(3)

The reactive current driver 7 is made in the form of a limiter of the rate of change of the signal U and the rate of change of the signal U at its output does not exceed the possible rate of change of the magnetic flux in the asynchronous motor 1.

In the simplest case, the limiter 30 of the rate of change of the signal is an aperiodic link with a constant time T, the value of which is determined from the condition

5 r fls constant time chain

magnetizing induction motor 1. In this case, taking into account (2), receive:

40

. (four)

Pa of the output of the division unit 6 and the multiplication unit 11 taking into account (2) - (4) are respectively obtained:

45

U5 (1-bpT);

(five)

 U5 (1 + pT) SignU. 41 and G (6)

 five

The signals and and Ug are received respectively at the inputs 15 and 14 of the logical

50 switch 12, with which three operating modes are realized in the drive.

The first mode of operation of the AC drive is characterized by

55 constant in value cue of an induction motor, equal to (0.3-0.5), where1 () „is the nominal value of the flux linkage corresponding to saturation.

20

emit a signal equal to u

and 2)

Using the multiplication unit 10, a signal Uj equal to

, U, SignU.

(3)

The reactive current driver 7 is made in the form of a limiter of the rate of change of the signal U and the rate of change of the signal U at its output does not exceed the possible rate of change of the magnetic flux in the asynchronous motor 1.

In the simplest case, the limiter 30 of the rate of change of the signal is an aperiodic link with a constant time T, the value of which is determined from the condition

5 r fls constant time chain

magnetizing induction motor 1. In this case, taking into account (2), receive:

40

. (four)

Pa of the output of the division unit 6 and the multiplication unit 11 taking into account (2) - (4) are respectively obtained:

45

U5 (1-bpT);

(five)

 U5 (1 + pT) SignU. 41 and G (6)

 five

The signals and and Ug are received respectively at the inputs 15 and 14 of the logical

switch 12, with which three modes of operation are realized in the drive.

The first mode of operation of the AC drive is characterized by

Constant in value cue of an induction motor, equal to (0.3-0.5), where1 () „is the nominal value of the flux linkage corresponding to saturation.

71508

In this zone, there is no strict correspondence between the magnitude of the flux linkage and the ip signal of the task, in particular, due to the appearance of residual magnetization.

Minimizing power losses due to a change in the reactive component of the current does not make sense here, so

when the UQ signal changes and U const is maintained.

From the output of the unit 22 minimum reactive current signal Uy, equal to

. | lJ7,

(7)

Where

UH, the value of the control signal corresponding to the nominal flux linkage N is a coefficient equal to 0.3-0.5. The signal Uy is compared at the inputs of the comparison element 21 with the signal U. The considered first operating mode of the electric drive corresponds to the condition. At the same time, the elements 29 and 31 are open and at the outputs of the logic switch 12, the signals Ujj and Uq are generated, defined by the formulas

Uj,

(eight)

.

Taking into account (8), the expression for the moment in the first mode is determined by the formula

M U-N-nfu |, (9)

those. torque is a linear function of the control signal U.

The second mode of operation of the AC drive is characterized by a simultaneous change in the active and reactive components of the current; here, the problem of leveling the indicated components of the current in terms of the magnitude and minimum of the power loss is solved. The magnetic flux of the asynchronous motor is changed in the specified mode to Cj values).

In this mode, the condition is satisfied that the elements of And 29 and 31 are closed and the elements of H 28 and 30 are opened.

From the output of the generator 23 reactive current receives a signal that

compared to the signal U, at the inputs of the reference element 20. If, then And 24 and 26 elements are opened, and And 25 and 27 elements are closed. With

eight

at the outputs of the logical trans-: pt1U-trans 12, this is obtained taking into account (4). (6):

, - | fUr

(

 (i + pT) signu-- | ur. (ten)

jg

35

Q with 0

five

in view of (10), the expression for the moment in the second mode, is determined by the formula

,(eleven)

those. the moment is proportional to the control signal and. In this case, as it follows from (10), besides the 15th, equality of the active and reactive components of the current in the established modes of operation is fulfilled, and, therefore, the condition of minimum power loss is satisfied. (

20 In the third mode of operation of the AC drive, overload moments are obtained at a nominal value of flow equal to C (. Flow control is higher than

25 C) c is impractical, since, due to saturation of the engine, an increase in the flow can occur only due to a significant increase in the reactive current, determined by the signal Uj, of a task. An increase in the moment above the nominal value in the indicated mode occurs due to an increase in the active component of the current determined by the signal UQ of the reference. In this mode, the conditions are met and in which the elements H 25,27,28 and 30 open, and the elements 24,26,29 and 31 close. In this case, the outputs of the logic switch 12 receive:

Il, LE; one

. J (12) In view of (11), the expression for the moment in the third mode is determined by the formula

,(13)

those. the moment is linearly dependent on the control signal U and it is possible to obtain overload moments with a constant flow of the engine.

I

In all considered modes of operation of the AC drive, a high speed in the formation of the moment is provided, despite the presence of a constant time of the magnetization circuit.

By adjusting the torque to within the nominal value in static modes, the minimum power loss is achieved,

Thus, the introduction into the proposed AC drive of the square root extraction unit of the signal module, the signal sign determiner, the multiplication units and the logic switch for setting active and reactive currents provides a reduction in power loss.

Formula

An AC motor drive containing a squirrel cage rotor asynchronous motor connected to the output of a controlled current source, a reference terminal forwarder connected to a cage rotor asynchronous motor and connected to an input for reference signals of the coordinate converter unit, the output of which is connected to the control the input of the controlled current source, the control signal adjuster connected by the output with the input of the divisible division unit, the reactive current driver, the output of which is connected The divider of the divider unit is connected to the input, while the inputs for controlling the active and reactive currents of the transformer unit are associated respectively with the output of the divider unit and the output of the reactive current driver, characterized in that, in order to reduce power losses, extracting the square root of the signal module, the signal sign identifier, two multiplication units and a logical switch of active and reactive current setting signals, equipped with three inputs and connected by outputs to the same inputs d The control unit of the conversion unit, wherein the output of the control signal transmitter is connected to the interconnected input of the square root extraction unit of the signal module, the input of the signal sign detector and the first input of the active and reactive currents switch, the second and third inputs of which connected, respectively, to the output of the first multiplication unit and the output of the reactive current generator 0

0

five

0

five

0

five

0

five

ka, the output of the signal sign detector is connected to the first input of the second multiplication unit, the second input of which is combined with the input of the divisible division unit, the input of the reactive current driver and connected to the output of the square root extractor unit, the output of the second unit multiply podkorny The first time multiplication, the second input of which is connected to the output of the dividing unit, the reactive current driver being complete in the Reed of the signal speed limiter, and the logic switch of the reference signals active and reactive currents are provided with four 2-2I-2ILN elements with two comparison elements, a minimum reactive current indicator and a saturation reactive current indicator, while the second and third inputs of the first element 2-2N-21SHI and the second and third inputs of the second element 2 -2IL-2IL or interconnected and connected to the output of the first element of the comparison, the second and third inputs of the third element 2-2I -.OR, and the second and third in /; Ы fourth element 2-2I-2IL or volume, inn and connected to the output of the second element of the comparison, the output of the set points As the minimum reactive current is connected to the first input of the second comparison element and the fourth input of the fourth 2-2I-ORI element, interconnected, the output of the nastigena reactive current generator is connected to the first input of the first element combined between each other and the fourth input of the second element of the second 2 -2G1-21SHI, the first input of the logical switch of the active and reactive currents setting signals form the fourth inputs of the first and third 2-211-2ML elements between co6efi, the second input of the specified logical The switch forms the first input of the first element, the third input of the specified logical switch forms the interconnected second inputs of the comparison elements and the first input of the second element 2-211-2ILL, and the outputs of the logic switch for the active and response current signals form the third and the fourth element 2-211-210111.

Claims (2)

Claim An AC drive comprising a squirrel-cage induction motor connected to an output of a controlled current source, a reference signal generator 20 connected to an squirrel-cage induction motor and connected to an input for reference signals of a coordinate conversion unit, the output of which is connected to the input of the controlled current source, the control signal adjuster, connected by the output to the input of the divisible division unit, the reactive current driver, the output of which is connected censor to the input of the divider of the division unit, while the inputs for controlling the active and reactive currents of the coordinate conversion unit are connected respectively to the output of the division unit and the output of the reactive current driver, characterized in that, in order to reduce power losses, a square root extraction unit is introduced into it from the signal module, determine the signal signifier, two multiplication units and a logical switch for setting active and reactive currents, equipped with three inputs and connected to the inputs of the same name to control the pre- ^ 5 education unit, while the output of the control signal setter is connected to the input of the square root extraction unit from the signal module, the input of the sign identifier 50 of the signal, and the first input of the signal re-setter for setting the active and reactive currents, the second and third inputs of which respectively connected to the output of the first multiplication unit and 55 to the output of the reactive current driver, the output of the signal sign determinant is connected to the first input of the second multiplication unit, the second input of which is is single with the input of the divisible division unit, the input of the reactive current driver and connected to the output of the square root extractor from the signal module, the output of the second multiplication unit is connected to the first move of the first Zlek multiplication, the second input of which is connected to the output of the division unit, and the reactive current driver in the form of a limiter for the rate of change of the signal, and the logical switch of the signals for setting the active and reactive currents is equipped with four elements 2-2I-2 OR two elements of comparison, the master imal reactive current and saturation reactive current adjuster, while the second and third inputs of the first 2-2I-2 OR element and the second and third inputs of the second 2-2112 OR element are interconnected and connected to the output of the first comparison element, the second and third inputs of the third element 2 -2I-2ShSh and the second and third inputs of the fourth element. 2-2I2OR are interconnected and connected to the output of the second comparison element, the output of the minimum reactive current setter is connected to the first input of the second comparison element connected together me and the fourth input of the fourth element 2-2I-2OR, the output of the saturation reactive current generator is connected to the first input of the first comparison element and the fourth input of the second 2-2I-21SHI element connected together, the first input of the active and reactive current setting logic switch signals form the fourth inputs of the first and the third element 2-2I-2OR, the second input of the specified logical switch forms the first input of the first element 2-2I ~ 211LI, the third input of the specified logical switch forms the interconnected second inputs comparing the rows of elements and the first input of the second element 2-2I-2or and outputs a logic switch the active and reactive current reference signals constitute the outputs of the third and fourth members 2-2I-211LI.