SU1720136A1 - Variable current frequency electric drive - Google Patents

Abstract

The invention relates to electrical engineering and can be used in controlled electric drives with synchronous motors. The aim of the invention is to improve the energy performance and accuracy of the electric drive in a wide range of rotational frequencies. This goal is achieved by the fact that the current zone playback control unit 8 is equipped with a series-connected rotational speed converter 9, a fixed memory 10 with the possibility of implementing a special relationship and a digital-to-analog converter 11, the control unit b of the power converter 3 is equipped with a pulse distributor 12, and the comparator 7 is runnable. In this case, the total additional losses in the electric motor and power converter i are maintained at a minimum level throughout the entire frequency control range of the rotor. Reducing the width of the current path with increasing rotational speed leads to an increase in the accuracy of controlling the phase currents. 1 il. (L

Description

g

L

{.-

 yoo o

| not vh-e:

WITH

The invention relates to electrical engineering and can be used in adjustable electric drives with synchronous motors, for example, for autonomous installations, where energy indicators are decisive.

The purpose of the invention is to improve the energy performance and accuracy of the electric drive in a wide range of rotational speed control.

The drawing shows a structural scheme of the proposed electric drive,

The electric drive contains a synchronous two-phase electric motor 1 with a feedback sensor 2 mounted on its shaft, a power converter 3, the outputs of which are connected via the phase current sensor 4 to the windings of the electric motor 1, a driver of a sinusoidal reference signal 5, the first input of which is intended to supply a driving signal, the second the input is connected to the output of the feedback sensor 2, and the output of the shaper of the reference sinusoidal signal 5 is connected to the first input of the control unit 6 by the power converter 3, with the comparator 7 and connected by a second input to the output of the phase current sensor 4, the control unit for the current playback zone 8, connected by the input to the output of the feedback sensor 2, and the output to the third input of the control unit 6 by the power converter 3. In this case the zone control unit current playback 8 contains a serially connected converter speed - code 9, permanent memory 10 and digital-to-analog converter 11, the control unit 6 of the power converter 3 contains a distributor and The pulses 12, the output of which forms the output of the block 6, and the comparator 7 is controlled, and its two inputs and the control input form the first, second and third inputs of the control unit 6, respectively, of the power converter 3.

The drive works as follows.

When a master signal is applied that determines the required torque value of the electric motor 1, a signal is generated at the output of the reference sinusoidal signal generator 5, which sets the required phase currents of the electric motor 1. To implement frequency-current control by the electric motor 1, the reference signal of the phase currents changes in a sinusoidal shaft angle using a feedback sensor 2 connected to the second input of the driver of the reference sinusoidal signal 5.

The comparator 7 in the control unit 6 by the power converter 3 performs

phase comparison of the reference signal of the phase currents and the signal from the output of the phase currents sensor 4 and has a symmetrical relay characteristic with a hysteresis of 2 A g. The output signals of the comparator 7 through the pulse distributor 12 provide switching of the keys of the power converter 3. As a result of feedback from the phase relay arises

phase currents of the electric motor 1, while the currents in the phases differ from those set by the value of the pulsating component, the amplitude of which is constant and is determined by the width of the current corridor D ir, and the frequency

is changing. The width of the current corridor D | g in the proposed drive is automatically adjusted with the help of the control unit of the current playback area 8.

The frequency of the feedback sensor signal 2 Td is directly proportional to the frequency of rotation of the shaft of the electric motor 1

td-KdSh, (1)

converted by converter

Frequency code 9.Input code D of persistent storage device 10

0 Md-KpKdSh, (2).

the output code Q of which is fed to the digital-to-analog converter 11. Current

the value of the output signal of the digital-to-analog converter 11 determines the magnitude of the signal at the control input of the comparator 7 and thereby the width of the current corridor:

D1g KtsO. (3)

As a result, during the operation of the electric drive, the functional relationship of the width of the current corridor with the frequency of rotation of the shaft of the electric motor 1 is performed. The type of functional dependence is determined by the form of the function Q (D) recorded in the persistent storage device 10. In the proposed electric drive, the function Q (D) is defined of condition

minimum total additional losses in the engine 1 and the power converter 3 in the whole range of rotational speed control as follows. Additional Pulsation Loss

The currents in the windings of the electric motor 1 are proportional to the square of the width of the current corridor D1G:

Rd "-d-D1 (Russia + 2Rk). (four)

where Rf, RK are respectively the active resistances of the phase winding of the electric motor 1 and the open power switch of the power converter 3.

The switching losses of the power keys of the power converter 3, averaged over the period of the phase current, are inversely proportional to the current corridor A 1g:

H1 „

(five)

D lfn Ј

Рп ЗЦ, А | Г (1 ah where Еп is the supply voltage of the inverters of the power converter 3,

Im is the amplitude of the phase current of the electric motor 1,

C - inductance of the phase winding of the electric motor 1,

Gk is the on time (power) of the power switch of the power converter 3,

Angles - En (Ce-Itkf) 2 + ((Y) 2

/

D1. fafl-V Е 1tГкР (), 6) LMSU Y4 1f (Rf + 2 RK) W

Ce is the design parameter of the electric motor 1 (counter-emf coefficient),

P is the number of pairs of poles of the electric motor 1.

According to (4), (5), in order to minimize the total additional losses, it is necessary to adjust the width of the air current corridor as a function of the frequency of rotation of the solo law

s

Hence, taking into account (1) - (3), we define the function Q (D), which must be implemented in the persistent storage device 10

----

Q VK (1- (aD + b) 2-cP2), (7)

where the constants K, a, b, c depend on the parameters of the electric motor 1, the power switches of the power converter 3, the conversion factors of the feedback sensor 2-cd, the frequency converter 9-kp and the digital-analog converter 11 cts

En Im Tjc Cr

41f (T f + 2Px)

. but

Kp Kd EP

No

CP

Ulmp

Rn En

Thus, when implemented in the permanent storage device 10, the functions Q (D) of the form (7) in the proposed elec

ten

20

25

thirty

35

0

five

0

five

This drive automatically maintains the total additional losses in the electric motor 1 and the power converter 3 at a minimum level over the entire range of rotational speed control, which improves the energy performance of the electric drive. Reducing the width of the current path as the frequency of rotation increases leads to an increase in the accuracy of controlling the phase currents of the electric motor 1 and, consequently, the accuracy of the electric drive as a whole.

Claims (1)

An electric frequency-controlled electric drive containing a synchronous two-phase electric motor with a feedback sensor mounted on its shaft, a power converter whose outputs through the phase current sensor are connected to the windings of the electric motor, the driver of the reference sinusoidal signal, the first input of which is intended to supply the driving signal , the second input is connected to the output of the feedback sensor, and the output of the reference sine wave shaper is connected to the first input of the block the power converter, made with a comparator and connected by a second input to the output of the phase current sensor, a control unit for adjusting the current playback area connected to the output of the feedback sensor, and an output to the third input of the power converter control unit, characterized by that / in order to improve energy performance and accuracy in a wide range of frequency control of the motor shaft, the current zone control unit is equipped with a series-connected frequency converter — a code, a permanent storage device and a digital-junction converter, a power converter control unit — equipped with a pulse distributor, the output of which forms the output of the named block, and the comparator is controllable, with its two inputs and control input about form a respective first, second and third inputs of the power converter of the control unit, the comparator output is connected to the input of the pulse distributor, of a ROM unit reproducing control current zone configured to implement the following ratios: (1- (aD + b) 2-cD2). where Q, D are the output and input signals of the specified device, K.a.b.c are constants defined by the parameters of the main nodes of the electric drive: E2 | . UZ n lm to .ts 4 C, (Russia + 2 R) (UbnP 2 KpKdEp where Kd is the conversion coefficient of the feedback sensor (in terms of rotational speed), Kp, Kc are the conversion ratios of the frequency converter — the code and the digital-to-analog converter, respectively En is the power supply voltage of the power converter, Gk is the on / off time of the key elements of the power converter, RK is the active resistance of the open key element of the power converter, RF, C - active resistance and inductance of the phase winding of the electric motor, P - the number of pairs of poles of the motor, С «is a constructive parameter of an electric motor (counter-emf coefficient), lm is the amplitude of the motor phase current.