阅读说明：本技术 基于电流预测的适用于直线感应电机控制的死区补偿方法 (Dead zone compensation method suitable for linear induction motor control based on current prediction ) 是由 邹会杰 张涛 张吉斌 张瑞峰 詹哲军 梁海刚 于 2020-06-18 设计创作，主要内容包括：本发明涉及电机控制的死区补偿方法,具体为基于电流预测的适用于直线感应电机控制的死区补偿方法。解决现有技术死区补偿效果较差的问题。基于电流预测的适用于直线感应电机控制的死区补偿方法,根据电机运行的频率分为低速区死区补偿策略和高速区死区补偿策略；本发明通过预测电流进行死区补偿,解决了由于数字控制器存在一定延迟,本拍计算的结果到下一拍才进行更新,导致过零点附件死区补偿效果较差的问题。(The invention relates to a dead zone compensation method for motor control, in particular to a dead zone compensation method suitable for linear induction motor control based on current prediction. The problem of prior art blind spot compensation effect relatively poor is solved. The dead zone compensation method based on current prediction and suitable for the control of the linear induction motor is divided into a low-speed zone dead zone compensation strategy and a high-speed zone dead zone compensation strategy according to the running frequency of the motor; the dead zone compensation is carried out through the prediction current, and the problem that due to the fact that a digital controller has certain delay, the calculated result of the beat is updated until the next beat, and the dead zone compensation effect of the zero-crossing point accessory is poor is solved.)

1. A dead zone compensation method suitable for linear induction motor control based on current prediction is characterized in that a low-speed zone dead zone compensation strategy and a high-speed zone dead zone compensation strategy are divided according to the running frequency of a motor;

when the motor runs at a low speed stage, firstly, the three-phase current i of the motor is converted into the three-phase current_A、i_BAnd i_Cαβ axis current i is obtained through a change formula of converting a three-phase static coordinate system into a two-phase static coordinate system_αAnd i_βThen i is_αAnd i_βObtaining MT axis current i through a change formula of converting a two-phase stationary coordinate system into a two-phase rotating coordinate system_MAnd i_T(ii) a Then calculating the obtained i_MAnd i_TThe predicted αβ axis current i is obtained through a change formula of converting a two-phase rotating coordinate system into a two-phase static coordinate system_{α_pre}And i_{β_pre}Where phi used for coordinate transformation passes phi + w_sT_sCalculated, wherein phi is the synchronous rotation angle of the next beat, theta is the synchronous rotation angle of the motor of the current beat, and w_sIs the synchronous angular frequency, T_sIs the sampling interval time; and obtaining the predicted three-phase current i of the motor by a change formula of converting the two-phase static coordinate system into the three-phase static coordinate system_{A_pre}、i_{B_pre}And i_{C_pre}(ii) a I obtained by calculation_{A_pre}、i_{B_pre}And i_{C_pre}Performing dead zone compensation;

when the motor runs at a high speed stage, firstly, the three-phase current i of the motor is converted into the three-phase current_A、i_BAnd i_Cαβ axis current i is obtained through a change formula of converting a three-phase static coordinate system into a two-phase static coordinate system_αAnd i_βThen i is_αAnd i_βObtaining MT axis current i through a change formula of converting a two-phase stationary coordinate system into a two-phase rotating coordinate system_MAnd i_T(ii) a Then calculating the obtained i_MAnd i_TThe excitation torque prediction current i under a rotating coordinate system is calculated through a stator voltage equation_{M_pre}And i_{T_pre}，i_{M_pre}And i_{T_pre}The predicted αβ axis current i is obtained through a change formula of converting a two-phase rotating coordinate system into a two-phase static coordinate system_{α_pre}And i_{β_pre}Where phi used for coordinate transformation passes phi + w_sT_sCalculated, wherein phi is the synchronous rotation angle of the next beat, theta is the synchronous rotation angle of the motor of the current beat, and w_sIs the synchronous angular frequency, T_sIs the sampling interval time; and obtaining the predicted three-phase current i of the motor by a change formula of converting the two-phase static coordinate system into the three-phase static coordinate system_{A_pre}、i_{B_pre}And i_{C_pre}(ii) a I obtained by calculation_{A_pre}、i_{B_pre}And i_{C_pre}Dead zone compensation is performed.

2. The dead zone compensation method for linear induction motor control based on current prediction as claimed in claim 1,

1) low-speed zone dead zone compensation strategy

Obtaining a current predicted value through coordinate transformation at a low-speed stage to perform dead zone compensation control, and specifically comprising the following steps:

3/2 transformation formula for transforming motor current from three-phase stationary coordinate system to two-phase stationary coordinate system:

in the formula i_A、i_BAnd i_CRespectively representing three-phase currents of the motor; i.e. i_α、i_βRespectively representing the currents of two static αβ coordinate axes;

2/2 transformation formula for transformation of motor current from two-phase stationary coordinate system to two-phase rotating coordinate:

in the formula i_α、i_βRespectively representing αβ coordinate axis currents i_M、i_TRespectively representing two-phase rotating MT coordinate axis currents; theta is the synchronous rotation angle of the motor;

the synchronous rotation angle of the next beat is changed into phi, phi is obtained through calculation of the synchronous rotation angle theta of the motor of the next beat, and a calculation formula is as follows:

φ＝θ+w_sT_s(3)

in the formula, w_sIs the synchronous angular frequency; t is_sIs the sampling interval time; phi, synchronously rotating the next beat;

then the αβ coordinate axis prediction current i is obtained by a change formula of converting a two-phase rotating coordinate system into a two-phase stationary coordinate_{α_pre}And i_{β_pre}The 2/2 transformation formula for transforming the two-phase rotating coordinate system to the two-phase stationary coordinate system is:

in the formula i_{α_pre}、i_{β_pre}Respectively representing αβ coordinate axis predicted current;

finally, obtaining the three-phase stationary coordinate axis prediction current i through a change formula of converting the two-phase stationary coordinate system to the three-phase stationary coordinate system_{A_pre}、i_{B_pre}And i_{C_pre}2/3 transformation formula for transformation of motor current from two-phase stationary frame to three-phase stationary frame:

in the formula i_{A_pre}、i_{B_pre}And i_{C_pre}Respectively representing three-phase predicted currents of the motor;

2) high-speed zone dead zone compensation strategy

Linear induction motor end-of-viewIn a T-shaped equivalent circuit of the effect, L_m，L_sσ，L_rσ，R_s，R_rRespectively representing the excitation inductance, the primary leakage inductance, the secondary leakage inductance, the primary resistance and the secondary resistance when the speed is zero; the eddy current loss of the secondary end part is represented by the resistance of an excitation branch, and the excitation inductance also changes along with the primary speed v; the change rule of the excitation branch resistance and the excitation inductance is R_rf(Q)，L_m(1-f (Q)), wherein,

wherein D is the primary effective length; v is the primary velocity; rotor inductance L_r＝L_rσ+L_m；

The flux linkage equation for a linear induction motor is as follows:

in the formula, #_M、ψ_TIs stator M-axis and T-axis flux linkage; i.e. i_M、i_TIs stator M-axis and T-axis currents; psi_mIs rotor M-axis flux linkage; i.e. i_m、i_tIs rotor M-axis and T-axis currents; l 'of equivalent mutual inductance'_m＝L_m(1-f (Q)); equivalent stator inductance L'_s＝L_sσ+L_m(1-f (Q)); equivalent rotor inductance L'_r＝L_rσ+L_m(1-f(Q))；

Because the motor speed is higher, the voltage drop on the resistor can be ignored, and the stator voltage equation omitting the resistor voltage drop is as follows:

in the formula u_M、u_TRespectively representing MT coordinate axis voltage without resistance voltage drop; w is a_sRepresents the stator angular frequency; p represents the differential;

three-phase current i of three-phase current of motor_A、i_BAnd i_CI is obtained through a change formula of converting a three-phase static coordinate system into a two-phase static coordinate system_αAnd i_βThen i is_αAnd i_βI is obtained through a change formula of converting a two-phase static coordinate system into a two-phase rotating coordinate_MAnd i_T；

Exciting current change rate is measured by the exciting current i of this beat_MAnd a predicted value i_{M_pre}Obtaining the compound shown as a formula (11); similarly, the torque current change rate calculation formula is shown as (12);

in the formula i_{M_pre}、i_{T_pre}Respectively representing the predicted current of MT coordinate axes; i.e. i_M、i_TRepresenting MT coordinate axis current of the beat; t is_sIs the sampling interval time;

the compounds of formulae (11) and (12) can be introduced into the compounds of formulae (9) and (10)

Obtaining an excitation current prediction by the above equationValue i_{M_pre}And torque current predicted value i_{T_pre}；

The synchronous rotation angle of the next beat is changed into phi, phi is obtained through calculation of the synchronous rotation angle theta of the motor of the next beat, and a calculation formula is as follows:

φ＝θ+w_sT_s(15)

in the formula, w_sIs the synchronous angular frequency; theta is the synchronous rotation angle of the motor; phi, synchronously rotating the next beat;

then the αβ coordinate axis prediction current i is obtained by a change formula of converting a two-phase rotating coordinate system into a two-phase stationary coordinate_{α_pre}And i_{β_pre}The transformation formula for transforming the two-phase rotating coordinate system to the two-phase stationary coordinate is as follows:

in the formula i_{M_pre}、i_{T_pre}Respectively representing the predicted current of MT coordinate axes; i.e. i_{α_pre}、i_{β_pre}Respectively representing αβ coordinate axis predicted current;

finally, obtaining the three-phase stationary coordinate axis prediction current i through a change formula of converting the two-phase stationary coordinate system to the three-phase stationary coordinate system_{A_pre}、i_{B_pre}And i_{C_pre}The change formula of the motor current transformed from the two-phase static coordinate system to the three-phase static coordinate system is as follows:

in the formula i_{A_pre}、i_{B_pre}And i_{C_pre}Respectively representing the predicted current of the three phases of the motor.

Technical Field

The invention relates to a dead zone compensation method for motor control, in particular to a dead zone compensation method suitable for linear induction motor control based on current prediction.

Background

Compared with the traditional track traffic technology, the medium-low speed maglev train has the following characteristics: the vibration and the noise are small in the running process of the train; the train has the characteristics of small turning radius, strong climbing capability, overcoming of adhesion limitation, small mechanical noise and abrasion of the train, reduction of vehicle maintenance cost and the like, so that the train is more and more widely applied.

The linear induction motor is used as a power source of the magnetic-levitation train, the main circuit topology of the inverter generally adopts a bridge circuit structure, and the switching devices of bridge arms adopt high-voltage-level IGBTs. Because the IGBT is not an ideal device and has turn-on and turn-off delay, certain dead time needs to be added into the upper IGBT driving pulse and the lower IGBT driving pulse of the same bridge arm to ensure the reliable work of the switching device; the turn-on and turn-off delay of the high-voltage level IGBT is more serious, so in order to ensure the reliable work of devices, longer dead time needs to be added to the driving pulse of the upper and lower tubes, the added dead time can cause the problem that the actual output voltage waveform is inconsistent with the theoretical voltage waveform, so that a dead time effect is caused, the dead time effect can generate harmonic voltage and current with different frequencies, the operation of a motor is influenced, particularly, the dead time effect is worse under the working condition of low-speed light load of a variable-frequency speed control system, and therefore the dead time needs to be compensated.

Disclosure of Invention

The invention solves the problem of poor dead zone compensation effect in the prior art, and provides a dead zone compensation method suitable for controlling a linear induction motor based on current prediction aiming at dead zone compensation control of the linear induction motor. The method predicts the motor current by combining coordinate transformation and a linear induction motor equivalent model, and performs dead zone compensation by predicting the motor current.

The invention is realized by adopting the following technical scheme: the dead zone compensation method based on current prediction and suitable for the control of the linear induction motor is divided into a low-speed zone dead zone compensation strategy (below rated frequency) and a high-speed zone dead zone compensation strategy (above rated frequency) according to the running frequency of the motor;

when the motor runs at a low speed stage (below a rated frequency), firstly, three-phase currents i of the motor are supplied_A、i_BAnd i_Cαβ axis current i is obtained through a change formula of converting a three-phase static coordinate system into a two-phase static coordinate system_αAnd i_βThen i is_αAnd i_βObtaining MT axis current i through a change formula of converting a two-phase stationary coordinate system into a two-phase rotating coordinate system_MAnd i_T(ii) a Then calculating the obtained i_MAnd i_TThe predicted αβ axis current i is obtained through a change formula of converting a two-phase rotating coordinate system into a two-phase static coordinate system_{α_pre}And i_{β_pre}Where phi used for coordinate transformation passes phi + w_sT_sCalculated, wherein phi is the synchronous rotation angle of the next beat, theta is the synchronous rotation angle of the motor of the current beat, and w_sIs the synchronous angular frequency, T_sIs the sampling interval time; and obtaining the predicted three-phase current i of the motor by a change formula of converting the two-phase static coordinate system into the three-phase static coordinate system_{A_pre}、i_{B_pre}And i_{C_pre}(ii) a I obtained by calculation_{A_pre}、i_{B_pre}And i_{C_pre}Performing dead zone compensation;

when the motor runs at a high speed stage (above rated frequency), firstly, the three-phase current i of the motor is converted into the three-phase current_A、i_BAnd i_CBy three-phase restThe αβ axis current i is obtained by a change formula of converting the coordinate system into a two-phase static coordinate system_αAnd i_βThen i is_αAnd i_βObtaining MT axis current i through a change formula of converting a two-phase stationary coordinate system into a two-phase rotating coordinate system_MAnd i_T(ii) a Then calculating the obtained i_MAnd i_TThe excitation torque prediction current i under a rotating coordinate system is calculated through a stator voltage equation_{M_pre}And i_{T_pre}，i_{M_pre}And i_{T_pre}The predicted αβ axis current i is obtained through a change formula of converting a two-phase rotating coordinate system into a two-phase static coordinate system_{α_pre}And i_{β_pre}Where phi used for coordinate transformation passes phi + w_sT_sCalculated, wherein phi is the synchronous rotation angle of the next beat, theta is the synchronous rotation angle of the motor of the current beat, and w_sIs the synchronous angular frequency, T_sIs the sampling interval time; and obtaining the predicted three-phase current i of the motor by a change formula of converting the two-phase static coordinate system into the three-phase static coordinate system_{A_pre}、i_{B_pre}And i_{C_pre}(ii) a I obtained by calculation_{A_pre}、i_{B_pre}And i_{C_pre}Dead zone compensation is performed.

The dead zone compensation is carried out through the prediction current, and the problem that due to the fact that a digital controller has certain delay, the calculated result of the beat is updated until the next beat, and the dead zone compensation effect of the zero-crossing point accessory is poor is solved.

Drawings

FIG. 1 is a schematic diagram of current closed loop control during a low speed phase;

FIG. 2 is a diagram of a main circuit topology employed in the present invention;

FIG. 3 is i_{A_pre}0 dead zone compensation schematic diagram;

FIG. 4 shows i_{A_pre}< 0 dead zone compensation schematic diagram;

FIG. 5 is a schematic diagram of the current open loop control during the high speed phase;

FIG. 6 is a T-shaped equivalent circuit diagram of a linear induction motor considering end effects;

FIG. 7 is an equivalent circuit diagram of a secondary magnetic field orientation M axis of the linear induction motor;

fig. 8 is an equivalent circuit diagram of a secondary magnetic field orientation T axis of the linear induction motor.

Detailed Description

The dead zone compensation method based on current prediction and suitable for the control of the linear induction motor is divided into a low-speed zone dead zone compensation strategy (below rated frequency) and a high-speed zone dead zone compensation strategy (above rated frequency) according to the running frequency of the motor;

1) low speed zone dead zone compensation strategy (below rated frequency)

In the low-speed stage, the control strategy adopts current closed-loop control, and the principle is shown in figure 1; the motor current value is predicted by coordinate transformation.

Obtaining a current predicted value through coordinate transformation at a low-speed stage to perform dead zone compensation control, and specifically comprising the following steps:

3/2 transformation formula for transforming motor current from three-phase stationary coordinate system to two-phase stationary coordinate system:

in the formula i_A、i_BAnd i_CRespectively representing three-phase currents of the motor; i.e. i_α、i_βRespectively representing two-phase stationary αβ axis currents.

2/2 transformation formula for transformation of motor current from two-phase stationary coordinate system to two-phase rotating coordinate:

in the formula i_α、i_βRespectively representing αβ coordinate axis currents i_M、i_TRespectively representing two-phase rotating MT coordinate axis currents; theta is the synchronous rotation angle of the motor of the beat.

The synchronous rotation angle of the next beat is changed into phi, phi is obtained through calculation of the synchronous rotation angle theta of the motor of the next beat, and a calculation formula is as follows:

φ＝θ+w_sT_s(3)

in the formula, w_sIs the synchronous angular frequency; t is_sIs the sampling interval time; phi is the synchronous rotation angle of the next beat.

Then the αβ coordinate axis prediction current i is obtained by a change formula of converting a two-phase rotating coordinate system into a two-phase stationary coordinate_{α_pre}And i_{β_pre}The 2/2 transformation formula for transforming the two-phase rotating coordinate system to the two-phase stationary coordinate system is:

in the formula i_{α_pre}、i_{β_pre}Respectively representing αβ coordinate axes predicted current.

Finally, obtaining the three-phase stationary coordinate axis prediction current i through a change formula of converting the two-phase stationary coordinate system to the three-phase stationary coordinate system_{A_pre}、i_{B_pre}And i_{C_pre}2/3 transformation formula for transformation of motor current from two-phase stationary frame to three-phase stationary frame:

in the formula i_{A_pre}、i_{B_pre}And i_{C_pre}Respectively representing the predicted current of the three phases of the motor.

I obtained by calculation of dead zone compensation module_{A_pre}、i_{B_pre}And i_{C_pre}Dead zone compensation is performed. The specific compensation process is as follows:

the main circuit topological structure adopted by the invention is that a three-phase voltage type inverter is shown in figure 2, A, B and C respectively represent three bridge arms of the inverter, and V1 and V2 correspond to an upper pipe and a lower pipe of the bridge arm A; v3 and V4 correspond to the upper and lower tubes of the B bridge arm; v5 and V6 correspond to the upper and lower tubes of the C arm.

Phase A is passed through judgment i_{A_pre}The polarity of the voltage is subjected to dead zone compensation, the voltage V1 and the voltage V2 correspond to two IGBT devices of an A-phase bridge arm, and when i is equal to the voltage I, the voltage I is analyzed through the driving pulse and the output voltage waveform of the voltage V1 and the voltage V2_{A_pre}At > 0, the dead band compensation strategy is shown in FIG. 3, where V_AOThe voltage representing point A to O is a theoretical voltage without dead zone addedPressing a waveform; v1_ pulse and V2_ pulse are drive pulses of V1 and V2, respectively.

When i is_{A_pre}When the voltage is more than 0, the V2 turn-off process is carried out by adding V1 after dead zone compensation, as shown in b) in FIG. 3, and the pulse of V1 and V_AOKeeping consistent, the pulse of V2 advances the dead time T _ dead to turn off; the process of turning off V2 by V1 is shown as c) in FIG. 3, and the added dead zone compensation pulse is the pulse of V1 and the pulse of V2_AOIn agreement, the pulse of V2 is delayed by the dead time T dead on.

When i is_{A_pre}If < 0, the compensation principle is as shown in FIG. 4.

When i is_{A_pre}When the voltage is less than 0, V1 is turned on after dead zone compensation, V2 is turned off as shown in b) in FIG. 4, and the pulse of V2 and V_AOKeeping the complementation, and turning on the pulse delay dead time T _ dead of V1; the process of turning off V2 by V1 is shown as c) in FIG. 4, and the added dead zone compensation pulse is the pulse of V2 and the pulse of V2_AORemaining complementary, the pulse of V1 is turned off early by the dead time T _ dead.

Phase B passing judgment i_{B_pre}Is dead zone compensated when i_{B_pre}When the value is more than 0, the compensation principle is shown in FIG. 3; when i is_{B_pre}If < 0, the compensation principle is as shown in FIG. 4. C phase passing judgment i_{C_pre}Is dead zone compensated when i_{C_pre}When the value is more than 0, the compensation principle is shown in FIG. 3; when i is_{C_pre}If < 0, the compensation principle is as shown in FIG. 4.

2) Dead zone compensation strategy of high speed zone (above rated frequency)

In the high-speed phase, the control strategy adopts current open-loop control, and the schematic diagram is shown in FIG. 5. And predicting the current value of the motor through the equivalent model of the linear induction motor.

A T-shaped equivalent circuit of the linear induction motor considering the end effect is shown in fig. 6.

In the T-type equivalent circuit of the linear induction motor considering the end effect, L_m，L_sσ，L_rσ，R_s，R_rRespectively representing the excitation inductance, the primary leakage inductance, the secondary leakage inductance, the primary resistance and the secondary resistance when the speed is zero. The eddy current loss at the secondary end is characterized by the resistance of the excitation branchThe magnetic inductance also varies with the primary velocity v. The change rule of the excitation branch resistance and the excitation inductance is R_rf(Q)，L_m(1-f (Q)), wherein,

wherein D is the primary effective length; v is the primary velocity; rotor inductance L_r＝L_rσ+L_m。

The equivalent circuit of the MT axis system according to the orientation of the secondary magnetic field is shown in figures 7 and 8.

The flux linkage equation for a linear induction motor is as follows:

in the formula, #_M、ψ_TIs stator M-axis and T-axis flux linkage; i.e. i_M、i_TIs stator M-axis and T-axis currents; psi_mIs rotor M-axis flux linkage; i.e. i_m、i_tIs rotor M-axis and T-axis currents; l 'of equivalent mutual inductance'_m＝L_m(1-f (Q)); equivalent stator inductance L'_s＝L_sσ+L_m(1-f (Q)); equivalent rotor inductance L'_r＝L_rσ+L_m(1-f (Q)). (in MT-axis coordinate system, the component of the rotor flux linkage in the M-axis is psi_mThe component in the T axis being psi_tSince the control is performed in accordance with the rotor field orientation, the rotor flux linkage and the M axis coincide, resulting in psi_tIs 0, thus the left side of the last term of equation 8 equals 0. )

Because the motor speed is higher, the voltage drop on the resistor can be ignored, and the stator voltage equation omitting the resistor voltage drop is as follows:

in the formula u_M、u_TRespectively representing MT coordinate axis voltage without resistance voltage drop; w is a_sRepresents the stator angular frequency; p represents the differential;

three-phase current i of three-phase current of motor_A、i_BAnd i_CI is obtained through a change formula of converting a three-phase static coordinate system into a two-phase static coordinate system_αAnd i_βThen i is_αAnd i_βI is obtained through a change formula of converting a two-phase static coordinate system into a two-phase rotating coordinate_MAnd i_T。

Exciting current change rate is measured by the exciting current i of this beat_MAnd a predicted value i_{M_pre}Obtaining the compound shown as a formula (11); similarly, the torque current change rate calculation formula is shown in (12).

In the formula i_{M_pre}、i_{T_pre}Respectively representing the predicted current of MT coordinate axes; i.e. i_M、i_TRepresenting MT coordinate axis current of the beat; t is_sIs the sampling interval time.

The compounds of formulae (11) and (12) can be introduced into the compounds of formulae (9) and (10)

Obtaining exciting current by the above formulaPredicted value i_{M_pre}And torque current predicted value i_{T_pre}I obtained by calculation_{M_pre}And i_{T_pre}And obtaining the current value of the motor after coordinate transformation.

The synchronous rotation angle of the next beat is changed into phi, phi is obtained through calculation of the synchronous rotation angle theta of the motor of the next beat, and a calculation formula is as follows:

φ＝θ+w_sT_s(15)

in the formula, w_sIs the synchronous angular frequency; theta is the synchronous rotation angle of the motor; phi is the synchronous rotation angle of the next beat.

Then the αβ coordinate axis prediction current i is obtained by a change formula of converting a two-phase rotating coordinate system into a two-phase stationary coordinate_{α_pre}And i_{β_pre}The transformation formula for transforming the two-phase rotating coordinate system to the two-phase stationary coordinate is as follows:

in the formula i_{M_pre}、i_{T_pre}Respectively representing the predicted current of MT coordinate axes; i.e. i_{α_pre}、i_{β_pre}Respectively representing αβ coordinate axes predicted current.

Finally, obtaining the three-phase stationary coordinate axis prediction current i through a change formula of converting the two-phase stationary coordinate system to the three-phase stationary coordinate system_{A_pre}、i_{B_pre}And i_{C_pre}The change formula of the motor current transformed from the two-phase static coordinate system to the three-phase static coordinate system is as follows:

in the formula i_{A_pre}、i_{B_pre}And i_{C_pre}Respectively representing the predicted current of the three phases of the motor.

I obtained by calculation of dead zone compensation module_{A_pre}、i_{B_pre}And i_{C_pre}Dead zone compensation is performed. Phase A is passed through judgment i_{A_pre}Is dead zone compensated when i_{A_pre}When the value is more than 0, the compensation principle is shown in FIG. 3; when i is_{A_pre}If < 0, the compensation principle is as shown in FIG. 4. Phase B passing judgment i_{B_pre}Is dead zone compensated when i_{B_pre}When the value is more than 0, the compensation principle is shown in FIG. 3; when i is_{B_pre}If < 0, the compensation principle is as shown in FIG. 4. C phase passing judgment i_{C_pre}Is dead zone compensated when i_{C_pre}When the value is more than 0, the compensation principle is shown in FIG. 3; when i is_{C_pre}If < 0, the compensation principle is as shown in FIG. 4.