阅读说明：本技术 异步电机最大转矩电流比控制方法及系统 (Method and system for controlling maximum torque current ratio of asynchronous motor ) 是由 胡冰 张利军 崔晓光 邵春伟 咸粤飞 张勋 李泽元 赵许强 袁超 谢峥 于 2020-07-28 设计创作，主要内容包括：本发明涉及一种异步电机最大转矩电流比控制方法,包括：根据转矩请求,在MTPA控制模式下,在交直轴电流等值正交分解条件下,确定直轴第一参考电流；同步将SVPWM调制中非零开关时间量在弱磁PI调节条件下,确定直轴第二参考电流；在非弱磁区和弱磁区频繁切换时,引入开关时间量阈值,将引入的开关时间量阈值与非零开关时间量比较,由直轴第一参考电流与直轴第二参考电流确定直轴电流参考值；由转矩请求和直轴电流参考值,确定交轴参考电流中间值,并根据最大滑差频率和峰值输出电流限制交轴参考电流中间值的幅值,确定交轴电流参考值。该方法解决了非弱磁区和弱磁区频繁切换时输出电流畸变的问题,实现异步电机全转速范围内最大转矩电流比控制。(The invention relates to a method for controlling the maximum torque current ratio of an asynchronous motor, which comprises the following steps: according to the torque request, under the MTPA control mode and under the condition of quadrature-axis and direct-axis current equivalent quadrature decomposition, determining a direct-axis first reference current; synchronously determining a second reference current of a direct axis for non-zero switching time in SVPWM under the condition of weak magnetic PI regulation; when the non-weak magnetic area and the weak magnetic area are frequently switched, introducing a switching time quantity threshold, comparing the introduced switching time quantity threshold with non-zero switching time quantity, and determining a direct-axis current reference value by using a direct-axis first reference current and a direct-axis second reference current; and determining a quadrature-axis reference current intermediate value according to the torque request and the direct-axis current reference value, and limiting the amplitude of the quadrature-axis reference current intermediate value according to the maximum slip frequency and the peak output current to determine the quadrature-axis current reference value. The method solves the problem of output current distortion when the non-weak magnetic region and the weak magnetic region are frequently switched, and realizes the maximum torque current ratio control within the full rotating speed range of the asynchronous motor.)

1. A method for controlling the maximum torque current ratio of an asynchronous motor is characterized by comprising the following steps:

according to torque requestIn the MTPA control mode, the relation between electromagnetic torque and quadrature-direct axis current is as follows:

synchronously determining a direct-axis second reference current I under the condition of weak magnetic PI regulation on the non-zero switching time amount in SVPWM modulation_{sd_ref2}；

When the non-weak magnetic area and the weak magnetic area are frequently switched, introducing a switching time quantity threshold, comparing the introduced switching time quantity threshold with non-zero switching time quantity, and using a direct-axis first reference current i_{sd_ref1}And a direct axis second reference current I_{sd_ref2}Determining a direct-axis current reference value I_{sd_ref}；

Requested by torque

According to the maximum slip frequency omega_smaxAnd peak output current I_smaxLimiting quadrature reference current median I_sq-ref1Upper and lower limit amplitude values of the reference value I of the quadrature axis current_{sq_ref}。

2. The maximum torque to current ratio control method of an asynchronous machine according to claim 1, characterized in that a direct-axis first reference current i is calculated_{sd_ref1}The specific method comprises the following steps:

generating a torque request from a throttle signal under a rotor field oriented vector control strategy

Limiting a straight-axis first reference current intermediate value I according to the output characteristics of the motor_{sd_ref1_mid}The upper limit of the amplitude of the upper limit is the amplitude of no-load current, the lower limit is the direct-axis weak magnetic current meeting the operation at the highest rotating speed, and a first reference current I of the direct axis is obtained_{sd_ref1}。

3. The maximum torque to current ratio control method of an asynchronous machine according to claim 2, characterized in that a direct axis second reference current I is calculated_{sd_ref2}The specific method comprises the following steps:

taking the non-zero switching time quantity of the last four switching periods in the SVPWM modulation, and obtaining the non-zero switching time quantity T after average filtering₁+T₂As a weak magnetic PI loop feedback value;

given a switching time reference value T_refAmount of non-zero switching time T₁+T₂Weakness after comparisonObtaining a second reference current intermediate value I through magnetic PI ring regulation_{sd_ref2_mid}：

Wherein: k_P、K_IIs PI regulation coefficient;

limiting the middle value I of the second reference current of the straight shaft according to the output characteristic of the motor_{sd_ref2_mid}The upper limit of the amplitude of the upper limit is the amplitude of no-load current, the lower limit is the direct-axis weak magnetic current meeting the operation at the highest rotating speed, and a second reference current I of the direct axis is obtained_{sd_ref2}。

4. Method for controlling the maximum torque to current ratio of an asynchronous machine according to claim 3, characterized in that the direct-axis current reference value I is determined_{sd_ref}The specific method comprises the following steps:

introducing a switching time quantity threshold value K₁*T_refIn which K is₁Is a constant less than 1 and greater than 0;

when non-zero switch time T₁+T₂＜K₁*T_refThen the direct axis current reference value I_{sd_ref}Equal to the first reference current I of the straight axis_{sd_ref1}I.e. I_{sd_ref}＝I_{sd_ref1}Weak magnetic PI loop integral gain inherits direct axis current reference value I in real time_{sd_ref}；

When non-zero switch time T₁+T₂≥K₁*T_refUsing a first reference current I of a straight axis_{sd_ref1}Limiting the second reference current I of the straight axis_{sd_ref2}After the upper limit value, let the direct-axis current reference value I_{sd_ref}Equal to the second reference current I of the straight axis_{sd_ref2}I.e. I_{sd_ref}＝I_{sd_ref2}。

5. Method for controlling the maximum torque to current ratio of an asynchronous machine according to any of claims 1-4, characterized in that it is based on the maximum slip frequency ω_smaxAnd peak output current I_smaxLimiting quadrature reference current median I_{sq_ref1}Upper and lower limit amplitude values of the reference value I of the quadrature axis current_{sq_ref}The method comprises the following steps:

obtaining peak current I from motor driver and asynchronous motor overload capacity_smaxFrom the direct-axis current reference value I_{sd_ref}And orthogonal decomposition is carried out on the quadrature-direct axis current, and quadrature-axis first limiting current is obtained through calculation:

obtaining the corresponding maximum slip according to the maximum torque, and setting the stator resistance R_sAfter 0, the maximum slip frequency is obtained:

wherein: r_rIs rotor resistance, L_sIs a stator inductance, L_rIs the rotor inductance, L_mThe stator and the rotor are mutually inducted;

from the maximum slip frequency omega_smaxCalculating to obtain a quadrature axis second limiting current:

wherein: t is_rIs the rotor time constant;

comparison I_{sq_max1}、I_{sq_max2}The smaller value is taken as the final quadrature axis limiting current I_{sq_max}I.e. I_{sq_max}＝min(I_sqmax1，I_{sq_max2})；

Limiting the current I by quadrature axis_{sq_max}To quadrature axis reference current intermediate value I_{sq_ref1}Performing upper and lower amplitude limiting to obtain quadrature axis current reference value I_{sq_ref}。

6. The maximum torque to current ratio control method of the asynchronous motor according to any one of claims 1 to 4, characterized by further comprising:

positioning a rotor of an electric machineAngle theta_rThe mechanical rotation speed omega is obtained by differential calculation_rWill slip frequency omega_sWith a mechanical speed omega_rThe sum integral is calculated to obtain the synchronous position angle theta_e。

7. The maximum torque to current ratio control method of an asynchronous machine according to claim 6, characterized by further comprising:

phase current I of motor_sa、I_sbAnd I_sa、I_sbDifference value of (I)_scAnd synchronous position angle theta_ePerforming synchronous rotation coordinate transformation to obtain direct-axis and quadrature-axis currents I_{sd_fdb}、I_{sq_fdb}。

8. The maximum torque to current ratio control method of an asynchronous machine according to claim 7, characterized by further comprising:

the direct axis and quadrature axis current I_{sd_fdb}、I_{sq_fdb}As a feedback current, with a reference value of the quadrature-direct axis current I_{sd_ref}、I_{sq_ref}The difference value is subjected to double-current PI closed-loop regulation to obtain direct-axis and quadrature-axis reference voltages

Reference voltage of direct axis and quadrature axisAnd synchronous position angle theta_eCarrying out Park inverse transformation to obtain reference voltage under a static coordinate system

Reference voltage in a stationary coordinate systemSwitching signals are obtained after SVPWM modulation and input to an inverter to control a motor, and the maximum torque current ratio control of an asynchronous motor is realizedAnd (5) preparing.

9. A maximum torque current ratio control system of an asynchronous motor comprises an inverter and the asynchronous motor; the direct-axis current reference value calculating unit is characterized by further comprising a direct-axis current reference value calculating unit, wherein the direct-axis current reference value calculating unit comprises a direct-axis first reference current calculating unit, a direct-axis second reference current calculating unit and a direct-axis current reference value judging unit;

the straight-shaft first reference current calculation unit is used for calculating a first reference current according to a torque requestUnder the MTPA control mode and under the condition of quadrature-axis and quadrature-axis current equivalent quadrature decomposition, a first reference current intermediate value I of a direct axis is obtained_{sd_ref1_mid}And performing amplitude limiting processing according to the output characteristic of the motor to determine a first reference current I of the direct axis_{sd_ref1}；

The direct-axis second reference current calculating unit is used for obtaining a direct-axis second reference current intermediate value I under the condition of weak magnetic PI regulation of non-zero switching time amount in SVPWM modulation_{sd_ref2_mid}And performing amplitude limiting processing according to the output characteristic of the motor to determine a second reference current I of the straight shaft_{sd_ref2}；

The direct-axis current reference value judging unit is used for introducing a switching time quantity threshold when a non-weak magnetic area and a weak magnetic area are frequently switched, comparing the introduced switching time quantity threshold with non-zero switching time quantity, and using a direct-axis first reference current i_{sd_ref1}And a direct axis second reference current I_{sd_ref2}Determining a direct-axis current reference value I_{sd_ref}。

10. The maximum torque current ratio control system of the asynchronous motor according to claim 9, further comprising a quadrature axis current reference value calculating unit, wherein the quadrature axis current reference value calculating unit comprises a quadrature axis reference current intermediate value calculating unit, a quadrature axis limit current calculating unit, and a quadrature axis current reference value determining unit;

the quadrature reference current intermediate value calculation unit is requested by torqueAnd a direct axis current reference value I_{sd_ref}Determining the quadrature reference current intermediate value I according to the electromagnetic torque formula_{sq_ref1}；

The quadrature axis limiting current calculating unit calculates the maximum slip frequency omega_smaxAnd peak output current I_smaxDetermination of quadrature axis limiting current I_{sq_max}；

The quadrature axis current reference value determination unit limits the current I by the quadrature axis_{sq_max}To quadrature axis reference current intermediate value I_{sq_ref1}Performing upper and lower amplitude limiting to determine quadrature axis current reference value I_{sq_ref}。

11. The asynchronous motor maximum torque current ratio control system according to claim 10, wherein the quadrature axis limiting current calculating unit includes a quadrature axis first limiting current calculating unit, a quadrature axis second limiting current calculating unit, and a quadrature axis limiting current determining unit;

the quadrature axis first limit current calculating unit is composed of a peak current I_smaxAnd a direct axis current reference value I_{sd_ref}Orthogonal decomposition of the quadrature-direct axis current to obtain a quadrature-axis first limiting current I_{sq_max1}；

The quadrature axis second limit current calculation unit is composed of a maximum slip frequency omega_smaxObtaining a quadrature axis second limiting current I_{sq_max2}；

The quadrature axis limiting current determination unit is used for taking I_{sq_max1}、I_{sq_max2}Is taken as the final quadrature axis limiting current I_{sq_max}。

12. The maximum torque to current ratio control system for an asynchronous motor according to any of claims 9-11, characterized by further comprising a synchronous position angle calculation unit for calculating the motor rotor position angle θ collected by the resolver_rThe mechanical rotation speed omega is obtained by differential calculation_rWill slip frequency omega_sWith a mechanical speed omega_rThe sum integral is calculated to obtain the synchronous bitSet angle theta_e。

13. The maximum torque to current ratio control system for an asynchronous motor according to claim 11, characterized in that it further comprises a 3s/2s transformation unit for transforming the phase current I collected_sa、I_sbAnd I_sa、I_sbDifference value of (I)_scAnd synchronous position angle theta_ePerforming synchronous rotation coordinate transformation to obtain direct-axis and quadrature-axis currents I_{sd_fdb}、I_{sq_fdb}。

14. The maximum torque current ratio control system of the asynchronous motor according to claim 13, further comprising a quadrature-direct axis PI adjusting unit, an Ipark transforming unit, and an SVPWM modulating unit;

the quadrature-direct axis PI adjusting unit: for applying direct and quadrature currents I_{sd_fdb}、I_{sq_fdb}As a feedback current, with a reference value of the quadrature-direct axis current I_{sd_ref}、I_{sq_ref}The difference value is subjected to double-current PI closed-loop regulation to obtain direct-axis and quadrature-axis reference voltages

The Ipark conversion unit is used for converting direct-axis and quadrature-axis reference voltagesAnd synchronous position angle theta_eCarrying out Park inverse transformation to obtain reference voltage under a static coordinate system

The SVPWM modulation unit: for reference voltages in a stationary frameThe inverter is subjected to SVPWM modulation for modulating the wave.

Technical Field

The invention belongs to the technical field of MTPA control, and particularly relates to a method and a system for controlling the maximum torque-current ratio of an asynchronous motor.

Background

At present, the maximum torque current ratio (MTPA) control strategy of most asynchronous motors is based on SVPWM modulation ratio feedback to realize the maximum utilization of battery voltage in a high-speed weak magnetic region, and does not relate to the current distribution of a non-weak magnetic region; meanwhile, when the three-phase asynchronous motor runs at a high speed, the problem of output current distortion exists due to frequent switching of a non-weak magnetic region and a weak magnetic region, and the system is unstable.

Therefore, the invention considers the improvement of the existing MTPA control strategy, so that the smooth transition of the optimal control of the torque current can be realized when the non-weak magnetic region and the weak magnetic region are frequently switched, and the stability and the reliability of the system are ensured.

Disclosure of Invention

The invention provides a method and a system for controlling the maximum torque-current ratio of an asynchronous motor, which determine a direct-axis current reference value according to the action time of a non-zero vector in space vector pulse modulation and a torque formula equivalent orthogonal decomposition strategy, realize smooth transition of optimal control of torque currents in a non-weak magnetic region and a weak magnetic region, limit the amplitude of a quadrature-axis current reference value when the slip angular frequency of each magnetic flux maximum torque is reached, and ensure the stability and reliability of the system.

In order to achieve the above object, the present invention provides a method for controlling a maximum torque current ratio of an asynchronous motor, comprising:

according to torque request

In the MTPA control mode, the relation between electromagnetic torque and quadrature-direct axis current is as follows:determining a first reference current i of a direct axis under the condition of quadrature-quadrature decomposition of the quadrature-direct axis current equivalent_{sd_ref1}(ii) a Wherein: l is_mFor stator-rotor mutual inductance, I_sq、I_sdThe current is alternating and direct axis current, and P is the number of pole pairs of the motor;

synchronously determining a direct-axis second reference current I under the condition of weak magnetic PI regulation on the non-zero switching time amount in SVPWM modulation_{sd_ref2}；

When the non-weak magnetic area and the weak magnetic area are frequently switched, introducing a switching time quantity threshold, comparing the introduced switching time quantity threshold with non-zero switching time quantity, and using a direct-axis first reference current i_{sd_ref1}And a direct axis second reference current I_{sd_ref2}Determining a direct-axis current reference value I_{sd_ref}；

Requested by torqueAnd a direct axis current reference value I_{sd_ref}Determining the quadrature reference current median value according to the electromagnetic torque formula

According to the maximum slip frequency omega_smaxAnd peak output current I_smaxLimiting quadrature reference current median I_{sq_ref1}Upper and lower limit amplitude values of the reference value I of the quadrature axis current_{sq_ref}。

Preferably, a direct-axis first reference current i is calculated_{sd_ref1}The specific method comprises the following steps:

generating a torque request from a throttle signal under a rotor field oriented vector control strategyWhen quadrature-axis current equivalent quadrature decomposition, i.e. I_sd＝I_sqThe torque current is optimal, and the relationship between the electromagnetic torque of the motor and the alternating current and direct current is as follows:obtaining the middle value I of the first reference current of the straight axis_{sd_ref1_mid}：

Limiting a straight-axis first reference current intermediate value I according to the output characteristics of the motor_{sd_ref1_mid}The upper limit of the amplitude of the upper limit is the amplitude of no-load current, the lower limit is the direct-axis weak magnetic current meeting the operation at the highest rotating speed, and a first reference current I of the direct axis is obtained_{sd_ref1}。

Preferably, a direct-axis second reference current I is calculated_{sd_ref2}The specific method comprises the following steps:

taking the non-zero switching time quantity of the last four switching periods in the SVPWM modulation, and obtaining the non-zero switching time quantity T after average filtering₁+T₂As a weak magnetic PI loop feedback value;

given a switching time reference value T_refAmount of non-zero switching time T₁+T₂After comparison, a second reference current intermediate value I is obtained through weak magnetic PI loop regulation_{sd_ref2_mid}：

Wherein: k_P、K_IIs PI regulation coefficient;

limiting the middle value I of the second reference current of the straight shaft according to the output characteristic of the motor_{sd_ref2_mid}The upper limit of the amplitude of the upper limit is the amplitude of no-load current, the lower limit is the direct-axis weak magnetic current meeting the operation at the highest rotating speed, and a second reference current I of the direct axis is obtained_{sd_ref2}。

Preferably, a direct-axis current reference value I is determined_{sd_ref}The specific method comprises the following steps:

introducing a switching time quantity threshold value K₁*T_refIn which K is₁Is a constant less than 1 and greater than 0;

when non-zero switch time T₁+T₂＜K₁*T_refThen the direct axis current reference value I_{sd_ref}Equal to the first reference current I of the straight axis_{sd_ref1}I.e. I_{sd_ref}＝I_{sd_ref1}Weak magnetic PI loop integral gain inherits direct axis current reference value I in real time_{sd_ref}；

When non-zero switch time T₁+T₂≥K₁*T_refUsing a first reference current I of a straight axis_{sd_ref1}Limiting the second reference current I of the straight axis_{sd_ref2}After the upper limit value, let the direct-axis current reference value I_{sd_ref}Equal to the second reference current I of the straight axis_{sd_ref2}I.e. I_{sd_ref}＝I_{sd_ref2}。

Preferably, according to the maximum slip frequency ω_smaxAnd peak output current I_smaxLimiting quadrature reference current median I_{sq_ref1}Upper and lower limit amplitude values of the reference value I of the quadrature axis current_{sq_ref}The method comprises the following steps:

obtaining peak current I from motor driver and asynchronous motor overload capacity_smaxFrom the direct-axis current reference value I_{sd_ref}And orthogonal decomposition is carried out on the quadrature-direct axis current, and quadrature-axis first limiting current is obtained through calculation:

obtaining the corresponding maximum slip according to the maximum torque, and setting the stator resistance R_sAfter 0, the maximum slip frequency is obtained:

wherein: r_rIs rotor resistance, L_sIs a stator inductance, L_rIs the rotor inductance, L_mThe stator and the rotor are mutually inducted;

from the maximum slip frequency omega_smaxCalculating to obtain a quadrature axis second limiting current:

wherein: t is_rIs the rotor time constant;

comparison I_{sq_max1}、I_{sq_max2}The smaller value is taken as the final quadrature axis limiting current I_{sq_max}I.e. by

Limiting the current I by quadrature axis_{sq_max}To quadrature axis reference current intermediate value I_{sq_ref1}Performing upper and lower amplitude limiting to obtain quadrature axis current reference value I_{sq_ref}。

Preferably, the method for controlling the maximum torque current ratio of the asynchronous motor further comprises:

positioning the rotor of the motor by an angle theta_rThe mechanical rotation speed omega is obtained by differential calculation_rWill slip frequency omega_sWith a mechanical speed omega_rThe sum integral is calculated to obtain the synchronous position angle theta_e。

Preferably, the method for controlling the maximum torque current ratio of the asynchronous motor further comprises:

phase current I of motor_sa、I_sbAnd I_sa、I_sbDifference value of (I)_scAnd synchronous position angle theta_ePerforming synchronous rotation coordinate transformation to obtain direct-axis and quadrature-axis currents I_{sd_fdb}、I_{sq_fdb}。

Preferably, the method for controlling the maximum torque current ratio of the asynchronous motor further comprises:

the direct axis and quadrature axis current I_{sd_fdb}、I_{sq_fdb}As a feedback current, with a reference value of the quadrature-direct axis current I_{sd_ref}、I_{sq_ref}The difference value is subjected to double-current PI closed-loop regulation to obtain direct-axis and quadrature-axis reference voltages

Reference voltage of direct axis and quadrature axis

And synchronous position angle theta_eCarrying out Park inverse transformation to obtain reference voltage under a static coordinate system

Reference voltage in a stationary coordinate systemAnd obtaining a switching signal after SVPWM modulation and inputting the switching signal to an inverter control motor to realize the control of the maximum torque current ratio of the asynchronous motor.

The invention also provides a maximum torque current ratio control system of the asynchronous motor, which comprises an inverter and the asynchronous motor; the direct-axis current reference value calculating unit comprises a direct-axis first reference current calculating unit, a direct-axis second reference current calculating unit and a direct-axis current reference value judging unit;

the straight-shaft first reference current calculation unit is used for calculating a first reference current according to a torque request

Under the MTPA control mode and under the condition of quadrature-axis and quadrature-axis current equivalent quadrature decomposition, a first reference current intermediate value I of a direct axis is obtained_{sd_ref1_mid}And performing amplitude limiting processing according to the output characteristic of the motor to determine a first reference current I of the direct axis_{sd_ref1}；

The direct-axis second reference current calculating unit is used for obtaining a direct-axis second reference current intermediate value I under the condition of weak magnetic PI regulation of non-zero switching time amount in SVPWM modulation_{sd_ref2_mid}And performing amplitude limiting processing according to the output characteristic of the motor to determine a second reference current I of the straight shaft_{sd_ref2}；

The straight axis current reference value determination unitWhen the non-weak magnetic region and the weak magnetic region are frequently switched, a switching time quantity threshold value is introduced, the introduced switching time quantity threshold value is compared with the non-zero switching time quantity, and the direct-axis first reference current i_{sd_ref1}And a direct axis second reference current I_{sd_ref2}Determining a direct-axis current reference value I_{sd_ref}。

Preferably, the asynchronous motor maximum torque current ratio control system further comprises a quadrature axis current reference value calculating unit, wherein the quadrature axis current reference value calculating unit comprises a quadrature axis reference current intermediate value calculating unit, a quadrature axis limiting current calculating unit and a quadrature axis current reference value judging unit;

the quadrature reference current intermediate value calculation unit is requested by torqueAnd a direct axis current reference value I_{sd_ref}Determining the quadrature reference current intermediate value I according to the electromagnetic torque formula_{sq_ref1}；

The quadrature axis limiting current calculating unit calculates the maximum slip frequency omega_smaxAnd peak output current I_smaxDetermination of quadrature axis limiting current I_{sq_max}；

The quadrature axis current reference value determination unit limits the current I by the quadrature axis_{sq_max}To quadrature axis reference current intermediate value I_{sq_ref1}Performing upper and lower amplitude limiting to determine quadrature axis current reference value I_{sq_ref}。

Preferably, the quadrature axis limiting current calculating unit includes a quadrature axis first limiting current calculating unit, a quadrature axis second limiting current calculating unit, and a quadrature axis limiting current determining unit;

the quadrature axis first limit current calculating unit is composed of a peak current I_smaxAnd a direct axis current reference value I_{sd_ref}Orthogonal decomposition of the quadrature-direct axis current to obtain a quadrature-axis first limiting current I_{sq_max1}；

The quadrature axis second limit current calculation unit is composed of a maximum slip frequency omega_smaxObtaining a quadrature axis second limiting current I_{sq_max2}；

The quadrature axis limiting current determination unit is used forGet I_{sq_max1}、I_{sq_max2}Is taken as the final quadrature axis limiting current I_{sq_max}。

Preferably, the asynchronous motor maximum torque current ratio control system further comprises a synchronous position angle calculation unit, which is used for calculating the motor rotor position angle θ collected by the rotary transformer_rThe mechanical rotation speed omega is obtained by differential calculation_rWill slip frequency omega_sWith a mechanical speed omega_rThe sum integral is calculated to obtain the synchronous position angle theta_e。

Preferably, the maximum torque current ratio control system of the asynchronous motor further comprises a 3s/2s transformation unit for transforming the collected phase current I_sa、I_sbAnd I_sa、I_sbDifference value of (I)_scAnd synchronous position angle theta_ePerforming synchronous rotation coordinate transformation to obtain direct-axis and quadrature-axis currents I_{sd_fdb}、I_{sq_fdb}。

Preferably, the maximum torque current ratio control system of the asynchronous motor further comprises a quadrature-direct axis PI adjusting unit, an Ipark conversion unit and an SVPWM modulating unit;

the quadrature-direct axis PI adjusting unit: for applying direct and quadrature currents I_{sd_fdb}、I_{sq_fdb}As a feedback current, with a reference value of the quadrature-direct axis current I_{sd_ref}、I_{sq_ref}The difference value is subjected to double-current PI closed-loop regulation to obtain direct-axis and quadrature-axis reference voltages

The Ipark conversion unit is used for converting direct-axis and quadrature-axis reference voltagesAnd synchronous position angle theta_eCarrying out Park inverse transformation to obtain reference voltage under a static coordinate system

The SVPWM modulation unit: for reference voltages in a stationary frameThe inverter is subjected to SVPWM modulation for modulating the wave.

Compared with the prior art, the invention has the advantages and positive effects that:

the invention provides a maximum torque current ratio control method of an asynchronous motor, which is characterized in that a strategy is generated based on new alternating current and direct axis current reference values, the direct axis current reference values are subjected to equivalent orthogonal decomposition calculation and weak magnetic ring PI regulation through a torque formula, and a switching time amount judgment condition is introduced to determine the final direct axis current reference value, so that the optimal torque current in a full rotating speed range can be ensured, the smooth switching of a weak magnetic region and a non-weak magnetic region is ensured, and the system can operate stably and reliably. Meanwhile, the maximum slip frequency and the peak output current of the weak magnetic area are introduced to limit the upper and lower limit amplitude values of the quadrature axis current reference value, so that the system can be ensured to stably and reliably operate in the deep weak magnetic area. The alternating current and direct current axis current reference value generation strategy solves the problem of output current distortion when a non-weak magnetic region and a weak magnetic region are frequently switched, and realizes maximum torque current ratio control in a full rotating speed range of a three-phase asynchronous motor. Meanwhile, according to the method, the invention also provides a corresponding control system for the maximum torque-current ratio of the asynchronous motor.

Drawings

FIG. 1 is a block diagram of the maximum torque to current ratio control for a three-phase asynchronous motor according to the present invention;

FIG. 2 is a flow chart of direct axis current reference generation;

FIG. 3 is a flow chart of cross-axis current reference generation.

Detailed Description

The following further describes embodiments of the present invention with reference to the accompanying drawings.

Aiming at the practical application working condition of the electric automobile, the embodiment of the invention not only has a very wide weak magnetic area to ensure that the asynchronous motor can run at a high speed, but also ensures the optimal control of the torque current to ensure that the battery efficiency reaches the practical requirement of maximum utilization, and considers to provide a maximum torque current ratio control method of the asynchronous motor, which is used for realizing the maximum torque current ratio control of the three-phase asynchronous motor for the electric automobile in the full rotating speed range, and ensures the stability of frequent switching between the non-weak magnetic area and the weak magnetic area through a reasonable alternating-direct axis reference current generation strategy.

The maximum torque current ratio (MTPA) control method is based on a direct current PI control structure of a d-axis and q-axis rotating coordinate system, a control block diagram is shown in figure 1, an exciting current d-axis is called as a direct axis, a torque current q-axis is called as a quadrature axis, a new generation strategy is provided aiming at a direct axis current reference value and a quadrature axis current reference value, namely the direct axis current reference value is reasonably selected according to the acting time of a non-zero vector in space vector pulse modulation and a torque formula equivalent orthogonal decomposition strategy, smooth transition of torque current optimal control in a non-weak magnetic area and a weak magnetic area is realized, a weak magnetic boundary is automatically identified, the upper and lower limits of the amplitude value of the quadrature axis current reference value are limited when the slip angular frequency of each magnetic flux maximum torque is reached, and the stability and reliability of a system are ensured. The control method of the maximum torque current ratio of the asynchronous motor specifically comprises the following steps:

(1) calculating a direct-axis current reference value I_{sd_ref}：

This embodiment proposes a direct-axis current reference value I_{sd_ref}Generating strategy, namely generating a direct-axis first reference current i through quadrature resolution of quadrature-to-quadrature axis current equivalent_{sd_ref1}Generating a direct-axis second reference current I by carrying out PI regulation on the sum of non-zero space voltage vector and weak magnetism_{sd_ref2}The two work simultaneously; when the non-weak magnetic area and the weak magnetic area are frequently switched, a final direct-axis current reference value I is generated by introducing a switching time amount threshold value_{sd_ref}. As shown in fig. 1 and fig. 2, the specific method is as follows:

according to the torque request

In the MTPA control mode, the relation between electromagnetic torque and quadrature-direct axis current is as follows:at a time of direct and alternating currentDetermining a first reference current i of a direct axis under the condition of equivalent orthogonal decomposition of the axis current_{sd_ref1}(ii) a Wherein: l is_mFor stator-rotor mutual inductance, I_sq、I_sdThe current is the alternating current and the direct current, and P is the number of pole pairs of the motor. The method specifically comprises the following steps:

generating a torque request from a throttle signal under a rotor field oriented vector control strategyWhen the quadrature axis current equivalent is orthogonally decomposed, i.e. I_sd＝I_sqThe torque current is optimal, and the relationship between the electromagnetic torque of the motor and the alternating current and direct current is as follows:obtaining the middle value I of the first reference current of the straight axis_{sd_ref1_mid}：

Then, limiting the middle value I of the first reference current of the direct axis according to the output characteristic of the motor_{sd_ref1_mid}The upper limit of the amplitude of the upper limit is the amplitude of no-load current, the lower limit is the direct-axis weak magnetic current meeting the operation at the highest rotating speed, and a first reference current I of the direct axis is obtained_{sd_ref1}。

Determining a second reference current I of a direct axis under the condition of synchronously adjusting the non-zero switching time amount in the SVPWM under the weak magnetic PI regulation condition_{sd_ref2}. The method specifically comprises the following steps:

taking the non-zero switching time quantity of the last four switching periods in the SVPWM modulation, and obtaining the non-zero switching time quantity T after average filtering₁+T₂As a weak magnetic PI loop feedback value;

given a switching time reference value T_refAmount of non-zero switching time T₁+T₂After comparison, a second reference current intermediate value I is obtained through weak magnetic PI loop regulation_{sd_ref2_mid}：

Wherein: k_P、K_IFor PI regulation factor, switching time reference value T_refGenerally 0.9-0.96, T₁+T₂Has been per unit.

Then, limiting the middle value I of the second reference current of the direct axis according to the output characteristic of the motor_{sd_ref2_mid}The upper limit of the amplitude of the upper limit is the amplitude of no-load current, the lower limit is the direct-axis weak magnetic current meeting the operation at the highest rotating speed, and a second reference current I of the direct axis is obtained_{sd_ref2}. It should be noted that the first reference current I of the direct axis in this embodiment_{sd_ref1}And a direct axis second reference current I_{sd_ref2}The determination of (2) needs to be performed synchronously.

Thirdly, when the non-weak magnetic area and the weak magnetic area are frequently switched, a switching time quantity threshold value K is introduced₁*T_refIn which K is₁Is a constant less than 1 and greater than 0;

amount of switching time threshold K to be introduced₁*T_refAmount of non-zero switching time T₁+T₂Comparing when the switching time is not zero₁+T₂＜K₁*T_refThen the direct axis current reference value I_{sd_ref}Equal to the first reference current I of the straight axis_{sd_ref1}I.e. I_{sd_ref}＝I_{sd_ref1}Weak magnetic PI loop integral gain inherits direct axis current reference value I in real time_{sd_ref}(ii) a When non-zero switch time T₁+T₂≥K₁*T_refUsing a first reference current I of a straight axis_{sd_ref1}Limiting the second reference current I of the straight axis_{sd_ref2}After the upper limit value, and making the direct-axis current reference value I_{sd_ref}Equal to the second reference current I of the straight axis_{sd_ref2}I.e. I_{sd_ref}＝I_{sd_ref2}。

(2) Calculating quadrature axis current reference value I_{sq_ref}Referring to fig. 1 and fig. 3, the specific method includes:

is requested by torqueAnd a direct axis current reference value I_{sd_ref}Determining the quadrature axis parameters according to an electromagnetic torque formulaMean value of test current

According to the maximum slip frequency omega_smaxAnd peak output current I_smaxLimiting quadrature reference current median I_{sq_ref1}Upper and lower limit amplitude values of the reference value I of the quadrature axis current_{sq_ref}. Specifically, the method comprises the following steps:

obtaining peak current I from motor driver and asynchronous motor overload capacity_smaxFrom the direct-axis current reference value I_{sd_ref}And orthogonal decomposition is carried out on the quadrature-direct axis current, and quadrature-axis first limiting current is obtained through calculation:

obtaining the corresponding maximum slip according to the maximum torque, and setting the stator resistance R_sAfter 0, the maximum slip frequency is obtained:

wherein: r_rIs rotor resistance, L_sIs a stator inductance, L_rIs the rotor inductance, L_mThe stator and the rotor are mutually inducted;

from the maximum slip frequency omega_smaxCalculating to obtain a quadrature axis second limiting current:

wherein: t is_rIs the rotor time constant;

comparison I_{sq_max1}、I_{sq_max2}The smaller value is taken as the final quadrature axis limiting current I_{sq_max}I.e. by

Limiting the current I by quadrature axis_{sq_max}To quadrature axis reference current medianI_{sq_ref1}Performing upper and lower amplitude limiting to obtain quadrature axis current reference value I_{sq_ref}。

(3) As shown in fig. 1, the method for controlling the maximum torque current ratio of the asynchronous motor in the present embodiment further includes the following steps:

positioning the rotor of the motor by an angle theta_rThe mechanical rotation speed omega is obtained by differential calculation_rWill slip frequency omega_sWith a mechanical speed omega_rThe sum integral is calculated to obtain the synchronous position angle theta_e；

Phase current I of motor_sa、I_sbAnd I_sa、I_sbDifference value of (I)_scAnd synchronous position angle theta_ePerforming synchronous rotation coordinate transformation to obtain direct-axis and quadrature-axis currents I_{sd_fdb}、I_{sq_fdb}；

The direct axis and quadrature axis current I_{sd_fdb}、I_{sq_fdb}As a feedback current, with a reference value of the quadrature-direct axis current I_{sd_ref}、I_{sq_ref}The difference value is subjected to double-current PI closed-loop regulation to obtain direct-axis and quadrature-axis reference voltages

Reference voltage of direct axis and quadrature axis

And synchronous position angle theta_eCarrying out Park inverse transformation to obtain reference voltage under a static coordinate system

Reference voltage in a stationary coordinate systemAnd switching signals obtained after SVPWM are input to an inverter control motor, so that the maximum torque current ratio control of the asynchronous motor is realized.

The maximum torque current ratio control method provided in the embodiment generates a strategy based on new alternating current and direct axis current reference values, performs equivalent orthogonal decomposition calculation and weak magnetic ring PI regulation on the direct axis current reference values through a torque formula, works in two ways at the same time, determines the final direct axis current reference value by introducing a switching time quantum judgment condition, can ensure that the torque current is optimal in a full rotating speed range, and ensures smooth switching between a weak magnetic area and a non-weak magnetic area, so that the system can operate stably and reliably. Meanwhile, the maximum slip frequency of the weak magnetic region and the peak output current of the controller are introduced to limit the upper and lower limit amplitude values of the quadrature axis current reference value, so that the system can be ensured to stably and reliably operate in the deep weak magnetic region. The alternating current and direct current axis current reference value generation strategy solves the problem of output current distortion when a non-weak magnetic region and a weak magnetic region are frequently switched, and realizes maximum torque current ratio control of a three-phase asynchronous motor for an electric automobile in a full rotating speed range.

According to the above method for controlling the maximum torque current ratio of the asynchronous motor, the present invention further provides a corresponding system for controlling the maximum torque current ratio of the asynchronous motor, as shown in fig. 1, which includes a direct axis current reference value calculating unit, a quadrature axis current reference value calculating unit, a synchronous position angle calculating unit, a 3s/2s converting unit, a quadrature axis PI adjusting unit, an Ipark converting unit, and an SVPWM modulating unit. Each unit is specifically as follows:

the direct-axis current reference value calculating unit comprises a direct-axis first reference current calculating unit, a direct-axis second reference current calculating unit and a direct-axis current reference value judging unit. Wherein:

a direct-axis first reference current calculation unit: for dependent on torque request

Under the MTPA control mode and under the condition of quadrature-axis and quadrature-axis current equivalent quadrature decomposition, a first reference current intermediate value I of a direct axis is obtained_{sd_ref1_mid}And performing amplitude limiting processing according to the output characteristic of the motor to determine a first reference current I of the direct axis_{sd_ref1}。

A direct-axis second reference current calculation unit: the method is used for obtaining a straight-axis second reference current intermediate value I under the condition of weak magnetic PI regulation of non-zero switching time amount in SVPWM modulation_{sd_ref2_mid}And according to the output characteristics of the motorLimiting the amplitude of the current to determine a second reference current I_{sd_ref2}。

Direct-axis current reference value determination unit: for comparing the introduced switching time threshold with the non-zero switching time by introducing the switching time threshold when the non-weak magnetic region and the weak magnetic region are frequently switched, and using the direct-axis first reference current i_{sd_ref1}And a direct axis second reference current I_{sd_ref2}Determining a direct-axis current reference value I_{sd_ref}。

The quadrature axis current reference value calculating unit comprises a quadrature axis reference current intermediate value calculating unit, a quadrature axis limiting current calculating unit and a quadrature axis current reference value judging unit. Wherein:

an intersection reference current intermediate value calculating unit: requested by torque

And a direct axis current reference value I_{sd_ref}Determining the quadrature reference current intermediate value I according to the electromagnetic torque formula_{sq_ref1}。

Quadrature axis limit current calculating unit: according to the maximum slip frequency omega_smaxAnd peak output current I_smaxDetermination of quadrature axis limiting current I_{sq_max}(ii) a The device specifically comprises a quadrature axis first limiting current calculating unit, a quadrature axis second limiting current calculating unit and a quadrature axis limiting current judging unit. Wherein the quadrature axis first limit current calculating unit is composed of a peak current I_smaxAnd a direct axis current reference value I_{sd_ref}Orthogonal decomposition of the quadrature-direct axis current to obtain a quadrature-axis first limiting current I_{sq_max1}(ii) a The quadrature axis second limiting current calculating unit calculates the maximum slip frequency omega_smaxObtaining a quadrature axis second limiting current I_{sq_max2}(ii) a The quadrature axis limiting current determination unit is used for taking I_{sq_max1}、I_{sq_max2}Is taken as the final quadrature axis limiting current I_{sq_max}。

Quadrature axis current reference value determination unit: limiting the current I by quadrature axis_{sq_max}To quadrature axis reference current intermediate value I_{sq_ref1}Performing upper and lower amplitude limiting to determine quadrature axis current reference value I_{sq_ref}。

Synchronous position angle meterA calculation unit: motor rotor position angle theta for collecting rotary transformer_rThe mechanical rotation speed omega is obtained by differential calculation_rWill slip frequency omega_sWith a mechanical speed omega_rThe sum integral is calculated to obtain the synchronous position angle theta_e。

3s/2s transformation unit: for phase current I to be collected_sa、I_sbAnd I_sa、I_sbDifference value of (I)_scAnd synchronous position angle theta_ePerforming synchronous rotation coordinate transformation to obtain direct-axis and quadrature-axis currents I_{sd_fdb}、I_{sq_fdb}。

A quadrature-direct axis PI regulation unit: for applying direct and quadrature currents I_{sd_fdb}、I_{sq_fdb}As feedback current, with reference value of AC and DC axis current_{sd_ref}、I_{sq_ref}The difference value is subjected to double-current PI closed-loop regulation to obtain direct-axis and quadrature-axis reference voltages

Ipark transformation unit: for referencing direct-axis and quadrature-axis voltagesAnd synchronous position angle theta_eCarrying out Park inverse transformation to obtain reference voltage under a static coordinate system

SVPWM modulation unit: for reference voltages in a stationary frameAnd carrying out SVPWM modulation on the inverter for modulating waves to realize the maximum torque current ratio control of the asynchronous motor.

The above description is only a preferred embodiment of the present invention, and not intended to limit the present invention in other forms, and any person skilled in the art may apply the above modifications or changes to the equivalent embodiments with equivalent changes, without departing from the technical spirit of the present invention, and any simple modification, equivalent change and change made to the above embodiments according to the technical spirit of the present invention still belong to the protection scope of the technical spirit of the present invention.