CN109981020B - Load self-adaption method - Google Patents

Abstract

The invention discloses a load self-adaption method, which is characterized in that when a load is reduced or output voltage is overlarge by introducing reactive current, the reactive current can be sharply increased due to the saturation of a motor magnetic field. The reactive voltage component at this time is reduced by the PI control. Since the active and reactive voltages are now still coupled together, a reduction in the reactive voltage will cause a simultaneous reduction in the active voltage. Therefore, the output voltage can automatically adapt to the change of the load when the load is increased or decreased, and the method is insensitive to the change of the motor parameters caused by the change of temperature, current and the like because excessive motor parameters are not involved. Therefore, motor parameters do not need to be accurately obtained before the power is supplied to the motor, the torque characteristic of the motor can be obviously improved when the power is supplied at a medium and low frequency, 1.5 times of the rated torque of the motor can be output to the maximum, and the current during no-load is close to the no-load current of the motor. The rotating speed of the motor driving different loads is close to the rated rotating speed, and the slip is obviously reduced.

Description

Load self-adaption method

Technical Field

The invention relates to a motor control method, in particular to a load self-adaption method.

Background

Generally, there are two methods for providing a variable frequency power supply for an asynchronous motor, one is VF control, that is, calculating an output voltage according to a given power supply frequency and a preset frequency-voltage curve, and then generating an SVPWM wave according to the power supply frequency and the output voltage to supply power to the motor. The disadvantage of this approach is that the output voltage and frequency cannot be adjusted to changes in the load. The debugging process needs to depend on the experience of debugging personnel and has limited effect. The other method is a vector control method based on rotor flux linkage orientation, and the method can independently control torque current and exciting current like a direct current motor through current decoupling, and has a good load self-adaption effect. But the problem is that motor parameters need to be accurately acquired, and the influence of motor parameter change in the control process is large. The realization process needs a large amount of calculation, and the debugging process is complex.

For the existing similar inventions, if the voltage compensation is performed only according to the current effective value or the active current, the current effective value after the voltage compensation is also increased, which leads to the single-phase dead cycle that the voltage and the current are continuously compensated and increased, and finally leads to the current overrun. It is also possible that the appropriate output voltage can be compensated for as the load increases, and that compensation cannot be exited as the load decreases, resulting in current over-limits.

Disclosure of Invention

The invention aims to provide a load self-adaption method which is simple in debugging method and insensitive to motor parameters.

The technical scheme adopted by the invention for solving the technical problems is as follows: a load self-adaptive method comprises the following steps:

1. a load self-adaptive method comprises the following steps:

A. the instantaneous value of the three-phase output current of the asynchronous motor is obtained through a three-phase current detection circuit and is recorded as i_A、i_B、i_C；

B. C, decomposing the three-phase output current instantaneous value clark conversion and park conversion obtained in the step A into active current and reactive current, and recording the reactive current as i_dThe active current is denoted as i_q，,i_αAnd i_βIs an intermediate variable, specifically:

C. will not work current i_dPerforming PI operation on the difference of the idle current I1 to obtain a reactive voltage Usm, wherein the idle current I1 is 1/3 rated current;

D. will have an active current i_qObtaining the active voltage Ust through proportional operation and filtering processing, which specifically comprises the following steps:

active voltage Ust ═ i_qK, said k being a scaling factor;

E. active current i_qThe slip fs is obtained through formula calculation, and specifically comprises the following steps:

namely:

wherein: te is an electromagnetic torque, n_pMotor pole pair number, Us phase voltage phasor amplitude, Rr rotor resistance, fs slip frequency, ω₁Is the electrical angular velocity, L_mIs the mutual inductance of the motor, L_rIs the motor rotor inductance, i_stIs the active current, #_rIs a magnetic flux; F. adding the slip fs and the frequency command F to obtain a new frequency command F^*，F^*＝(f^*+fs)；

G. According to the new frequency command F in step F^*Obtaining a compensated phase voltage vector U by using the active voltage Ust and the reactive voltage Usm^*Is concretely provided with

U_G＝F^*G, then U_GCompensating Us to obtain compensated phase voltage vector U^*G is a proportionality coefficient; compensated phase voltage vector U^*Transformed to obtain U_α ^*And U_β ^*，U_α ^*And U_β ^*Generating three-phase output voltages Uu, Uv, Uw, U by park inverse transformation_G、U_α ^*And U_β ^*Is an intermediate variable.

The invention has the beneficial effects that: the method does not involve excessive motor parameters and is insensitive to the change of the motor parameters caused by the change of temperature, current and the like, so that the motor parameters do not need to be accurately obtained before the power is supplied to the motor, the torque characteristic of the motor can be obviously improved when the power is supplied at a medium and low frequency, 1.5 times of the rated torque of the motor can be output to the maximum, and the current is close to the no-load current of the motor when the motor is in no-load. The rotating speed of the motor driving different loads is close to the rated rotating speed, and the slip is obviously reduced.

Drawings

Fig. 1 is a schematic diagram of a load adaptive method.

Detailed Description

The invention is further described with reference to the following figures and detailed description.

The invention discloses a load self-adaptive method, which comprises the following steps:

1. a load self-adaptive method comprises the following steps:

A. the instantaneous value of the three-phase output current of the asynchronous motor is obtained through a three-phase current detection circuit and is recorded as i_A、i_B、i_C；

B. C, decomposing the three-phase output current instantaneous value clark conversion and park conversion obtained in the step A into active current and reactive current, and recording the reactive current as i_dThe active current is denoted as i_q，,i_αAnd i_βIs an intermediate variable, specifically:

C. will not work current i_dPerforming PI operation on the difference of the idle current I1 to obtain a reactive voltage Usm, wherein the idle current I1 is 1/3 rated current;

the PI operation is the existing mature technology, the PI operation is not the invention point of the application, and the description is omitted;

D. will have an active current i_qObtaining the active voltage Ust through proportional operation and filtering processing, which specifically comprises the following steps:

active voltage Ust ═ i_qK, said k being a scaling factor, where the calculation of the active voltage is a common formula;

E. the active current is calculated by a formula to obtain a slip fs, which is specifically as follows:

namely:

wherein: te is an electromagnetic torque, n_pMotor pole pair number, Us phase voltage phasor amplitude, Rr rotor resistance, fs slip frequency, ω₁Is the electrical angular velocity, L_mIs the mutual inductance of the motor, L_rIs the motor rotor inductance, i_stIs the active current, #_rIs a magnetic flux;

F. adding the slip fs and the frequency command F to obtain a new frequency command F^*，F^*＝(f^*+fs)；

G. According to the new frequency command F in step F^*Obtaining a compensated phase voltage vector U by using the active voltage Ust and the reactive voltage Usm^*Is concretely provided with

U_G＝F^*G, then U_GCompensating Us to obtain compensated phase voltage vector U^*G is a proportionality coefficient; compensated phase voltage vector U^*Transformed to obtain U_α ^*And U_β ^*，U_α ^*And U_β ^*Generating three-phase output voltages Uu, Uv, Uw, U by park inverse transformation_G、U_α ^*And U_β ^*Is an intermediate variable.

The inverse clark transform and the inverse park transform described herein are well-established techniques and the formulas herein are not described in detail.

According to the invention, by introducing reactive current, when the load is too small or the output voltage is too large, the reactive current is increased sharply due to the saturation of the magnetic field of the motor, the reactive voltage component is reduced under the action of PI control, the active voltage and the reactive voltage are still coupled together, and the active voltage is reduced simultaneously due to the reduction of the reactive voltage. This allows the output voltage to automatically adapt to changes in the load as the load increases and decreases.

The following is a first example:

when used, the following are: 400kw, 2 antipodal asynchronous motor drag platform, motor rated 2563N.M, and 1.5 times motor rated torque of accompany-testing machine;

the following is a second example:

when used, the following are: 400kw, 2 antipodal asynchronous motor drag platform, rated 2563N.M, and 0.5 times motor rated torque of closed loop of the accompany-testing machine;

the above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are only exemplary embodiments of the present invention, and are not intended to limit the present invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (1)

1. A load self-adaptive method comprises the following steps:

A. the instantaneous value of the three-phase output current of the asynchronous motor is obtained through a three-phase current detection circuit and is recorded as i_A、i_B、i_C；

B. C, decomposing the three-phase output current instantaneous value clark conversion and park conversion obtained in the step A into active current and reactive current, and recording the reactive current as i_dThe active current is denoted as i_q，,i_αAnd i_βIs an intermediate variable, specifically:

C. will not work current i_dPerforming PI operation on the difference of the idle current I1 to obtain a reactive voltage Usm, wherein the idle current I1 is 1/3 rated current;

D. will have an active current i_qObtaining the active voltage Ust through proportional operation and filtering processing, which specifically comprises the following steps:

active voltage Ust ═ i_qK, said k being a scaling factor;

E. active current i_qThe slip frequency fs is obtained through formula calculation, and specifically comprises the following steps:

namely:

wherein: te is an electromagnetic torque, n_pMotor pole pair number, Us phase voltage phasor amplitude, Rr rotor resistance, fs slip frequency, ω₁Is the electrical angular velocity, L_mIs the mutual inductance of the motor, L_rIs the motor rotor inductance psi_rIs a magnetic flux;

F. adding the slip frequency fs and the frequency command F to obtain a new frequency command F^*，F^*＝(f^*+fs)；

G. According to the new frequency command F in step F^*Obtaining a compensated phase voltage vector U by using the active voltage Ust and the reactive voltage Usm^*Is concretely provided with

U_G＝F^*G, then U_GCompensating Us to obtain compensated phase voltage vector U^*G is a proportionality coefficient; compensated phase voltage vector U^*Transformed to obtain U_α ^*And U_β ^*，U_α ^*And U_β ^*Generating three-phase output voltages Uu, Uv, Uw, U by park inverse transformation_G、U_α ^*And U_β ^*Is an intermediate variable.

Images