阅读说明：本技术 一种基于异步调制的交流电机转矩控制方法及系统 (Asynchronous modulation-based alternating current motor torque control method and system ) 是由 杨大成 梅文庆 甘韦韦 周志宇 于 2018-07-17 设计创作，主要内容包括：本发明公开了一种基于异步调制的交流电机转矩控制方法及系统,包括：计算交流电机当前对应的调制比,并分别将调制比M与预设滞环下限M0及滞环上限M1比较；当M＜M0时,采用基于转子磁场定向的矢量控制系统,在线性区闭环控制交流电机的转矩；当M＞M1时,将获取的交流电机的转矩经PI闭环控制,以得到交流电机的电压矢量修正角,并将电压矢量修正角补偿给矢量控制系统中的坐标系变换角度,且根据矢量控制系统中两个PI控制器在过调制区的固定输出及补偿后的坐标系变换角度控制转矩；当M0≤M≤M1时,按照上一次比较结果对应的控制方式控制转矩。可见,本申请不存在耦合,且转矩调节准确,动态性好,提高了系统的可靠性及稳定性。(The invention discloses an alternating current motor torque control method and system based on asynchronous modulation, which comprises the following steps: calculating a current corresponding modulation ratio of the alternating current motor, and respectively comparing the modulation ratio M with a preset hysteresis lower limit M0 and a hysteresis upper limit M1; when M is less than M0, a vector control system based on rotor magnetic field orientation is adopted to control the torque of the alternating current motor in a linear region closed loop mode; when M is larger than M1, carrying out PI closed-loop control on the obtained torque of the alternating current motor to obtain a voltage vector correction angle of the alternating current motor, compensating the voltage vector correction angle to a coordinate system transformation angle in a vector control system, and controlling the torque according to the fixed output of two PI controllers in an overmodulation region and the compensated coordinate system transformation angle in the vector control system; and when M0 is more than or equal to M1, controlling the torque according to the control mode corresponding to the last comparison result. Therefore, the coupling does not exist, the torque is adjusted accurately, the dynamic performance is good, and the reliability and the stability of the system are improved.)

1. An AC motor torque control method based on asynchronous modulation is characterized by comprising the following steps:

calculating a current corresponding modulation ratio of the alternating current motor, and respectively comparing the modulation ratio M with a preset hysteresis lower limit M0 and a preset hysteresis upper limit M1;

when M is less than M0, a vector control system based on rotor magnetic field orientation is adopted to control the torque of the alternating current motor in a linear region closed loop mode;

when M is larger than M1, performing proportional integral PI closed-loop control on the acquired torque of the alternating current motor to obtain a voltage vector correction angle of the alternating current motor, compensating the voltage vector correction angle to a coordinate system transformation angle in the vector control system, and controlling the torque according to the fixed output of two PI controllers in an overmodulation region and the compensated coordinate system transformation angle in the vector control system;

and when M0 is more than or equal to M1, controlling the torque according to the control mode corresponding to the last comparison result.

2. The asynchronous modulation based alternating current motor torque control method as claimed in claim 1, wherein the vector control system based on the rotor magnetic field orientation is adopted, and the process of controlling the torque of the alternating current motor in a linear region closed loop mode is specifically as follows:

obtaining the exciting current i of the alternating current motor under a dq two-phase rotating coordinate system_sdAnd torque current i_sqAnd according to a given excitation current

correspondingly outputting the two difference values by adjusting the d-axis voltage compensation quantity delta u through two PI controllers_sdAnd q-axis voltage compensation amount Deltau_sqAnd will be Δ u_sd、Δu_sqCorresponding compensation gives u_sdc、u_sqcTo obtain a compensated d-axis voltage component u_sdAnd q-axis voltage component u_sq；

Obtaining a rotor field position angle theta of the AC machine_rAnd according to theta_rWill u_sd、u_sqConverting the dq two-phase rotating coordinate system into an alpha beta two-phase static coordinate system to obtain an alpha axis voltage component u_sαBeta axis voltage component u_sβ；

Will u_sα、u_sβAnd after Space Vector Pulse Width Modulation (SVPWM), controlling the on-state of a switch in an inverter connected with the alternating current motor so as to realize closed-loop control on the torque of the alternating current motor in a linear region.

3. The asynchronous modulation based alternating current motor torque control method of claim 2, wherein the obtaining the rotor field position angle θ of the alternating current motor_rThe process specifically comprises the following steps:

according to a predetermined integral formula theta_r＝∫(P_nω_m+ω_s1) dt, calculating the rotor field position angle theta of the AC machine_rWherein P is_nIs the number of pole pairs, omega_mIs the mechanical angular velocity, omega_s1Is the slip angular velocity.

4. The asynchronous modulation based alternating current motor torque control method of claim 2, wherein the obtaining the rotor field position angle θ of the alternating current motor_rThe process specifically comprises the following steps:

obtaining a rotor magnetic field position angle theta by utilizing a preset observation model of flux linkage torque of the alternating current motor_r；

The process of acquiring the torque of the alternating current motor is specifically as follows:

obtaining the torque T of the alternating current motor by using the observation model_e。

5. Asynchronous modulation based alternating current motor torque control method according to claim 4, characterized in that the observation model is in particular a voltage model.

6. The asynchronous modulation based alternating current motor torque control method according to claim 4, wherein the acquired alternating current motor torque is subjected to proportional integral PI closed loop control to obtain a voltage vector correction angle of the alternating current motor, the voltage vector correction angle is compensated for a coordinate system transformation angle in the vector control system, and the process of controlling the torque according to the fixed output of two PI controllers in an overmodulation region and the compensated coordinate system transformation angle in the vector control system is specifically as follows:

will T_eWith a given torque T_e ^*Making a difference, and regulating the difference value by PI to output a voltage vector correction angle delta theta of the alternating current motor_u；

Will delta theta_uAnd theta_rSumming to obtain a coordinate system transformation angle theta' corresponding to the overmodulation region of the vector control system, and under the premise that two PI controllers in the vector control system output fixedly, u is transformed according to theta_sd、u_sqConverting the dq two-phase rotating coordinate system into an alpha beta two-phase static coordinate system to obtain an alpha-axis voltage component u 'corresponding to the overmodulation region'_sαAnd beta-axis voltage component u'_sβ；

U's'_sα、u'_sβAnd controlling the on state of a switch in the inverter after SVPWM modulation so as to realize the control of the torque in an overmodulation region.

7. The asynchronous modulation based ac motor torque control method according to claim 6, wherein the difference is PI-adjusted to output a voltage vector correction angle Δ θ of the ac motor_uAfter that, the value of delta theta is adjusted_uAnd theta_rBefore summing, the method for controlling the torque of the alternating current motor further comprises the following steps:

according to the preset amplitude value pair Delta theta_uAnd carrying out amplitude limiting treatment to realize anti-overturn protection of the alternating current motor.

8. The asynchronous modulation based alternating current motor torque control method of claim 7, wherein the delta theta is based on a preset clipping amplitude value_uThe process of performing the amplitude limiting processing specifically includes:

according to

9. The asynchronous modulation based alternating current motor torque control method according to any one of claims 6 to 8, characterized in that Δ θ is made to be larger when the control mode corresponding to the overmodulation region is transited to the control mode corresponding to the linear region_uAnd adjusting to zero according to a preset slope.

10. An asynchronous modulation based AC motor torque control system, comprising:

the comparison module is used for calculating the current corresponding modulation ratio of the alternating current motor and comparing the modulation ratio M with a preset hysteresis lower limit M0 and a preset hysteresis upper limit M1 respectively;

the linear region control module is used for adopting a vector control system based on rotor magnetic field orientation to control the torque of the alternating current motor in a linear region closed loop mode when M is less than M0;

the overmodulation region control module is used for carrying out proportional integral PI closed-loop control on the acquired torque of the alternating current motor when M is larger than M1 to obtain a voltage vector correction angle of the alternating current motor, compensating the voltage vector correction angle to a coordinate system transformation angle in the vector control system, and controlling the torque according to fixed output of two PI controllers in an overmodulation region and the compensated coordinate system transformation angle in the vector control system;

and the hysteresis zone control module is used for controlling the torque according to the control mode corresponding to the last comparison result when M0 is more than or equal to M1.

Technical Field

The invention relates to the field of alternating current motor control, in particular to an alternating current motor torque control method and system based on asynchronous modulation.

Background

At present, the torque of alternating current machines is controlled by a vector based on the orientation of the rotor fieldThe vector control system adopts two PI (proportional-integral) controllers, and controls i of the alternating current motor under dq two-phase rotating coordinate system in a closed-loop mode_sd(excitation current) and i_sq(Torque current) corresponding to control u_sd(d-axis voltage component) and u_sq(q-axis voltage component), and further, the torque of the ac motor. However, the asynchronous modulation based ac motor is in two modulation modes: the theory research of a vector control system for controlling the torque of an alternating current motor in a linear region is mature, but the stable and accurate control of the torque of the alternating current motor cannot be realized in an overmodulation region because of the modulation ratio of the overmodulation regionM ∈ (0.907,1), where u_dcThe voltage of the over-modulation region is narrow, and closed-loop adjustment (easy over-adjustment) is not easy to realize, so that the accuracy of torque adjustment is reduced;

moreover, due to

Wherein R is_sAs the resistance of the stator,

for a given excitation current, ω_eIs the electrical angular velocity, L_σIn order to make the magnetic flux leakage,for a given torque current, L_sIs the stator inductance, so in the overmodulation region with nonlinear output and large harmonic wave_sdAnd u_sqThere is a severe coupling between them, which results in the vector control system substantially losing the torque regulation capability, thereby reducing the reliability and stability of the system.

Therefore, how to provide a solution to the above technical problem is a problem that needs to be solved by those skilled in the art.

Disclosure of Invention

The invention aims to provide an AC motor torque control method and system based on asynchronous modulation, which do not adopt PI regulation of two currents but adopt PI regulation of one torque, so that no coupling exists; in addition, the PI closed-loop control of the torque directly controls the torque by dynamically adjusting the voltage vector angle of the alternating current motor, the torque is accurately adjusted, the dynamic property is good, and therefore the reliability and the stability of the system are improved.

In order to solve the technical problem, the invention provides an alternating current motor torque control method based on asynchronous modulation, which comprises the following steps:

calculating a current corresponding modulation ratio of the alternating current motor, and respectively comparing the modulation ratio M with a preset hysteresis lower limit M0 and a preset hysteresis upper limit M1;

when M is less than M0, a vector control system based on rotor magnetic field orientation is adopted to control the torque of the alternating current motor in a linear region closed loop mode;

when M is larger than M1, performing proportional integral PI closed-loop control on the acquired torque of the alternating current motor to obtain a voltage vector correction angle of the alternating current motor, compensating the voltage vector correction angle to a coordinate system transformation angle in the vector control system, and controlling the torque according to the fixed output of two PI controllers in an overmodulation region and the compensated coordinate system transformation angle in the vector control system;

and when M0 is more than or equal to M1, controlling the torque according to the control mode corresponding to the last comparison result.

Preferably, the process of performing closed-loop control on the torque of the alternating current motor in a linear region by using a vector control system based on rotor magnetic field orientation specifically comprises:

obtaining the exciting current i of the alternating current motor under a dq two-phase rotating coordinate system_sdAnd torque current i_sqAnd according to a given excitation current

And given torque current

Calculating the original d-axis voltage component u_sdcAnd the original q-axis voltage component u_sqcAnd will be

Correspond to i_sd、i_sqMaking a difference;

correspondingly outputting the two difference values by adjusting the d-axis voltage compensation quantity delta u through two PI controllers_sdAnd q-axis voltage compensation amount Deltau_sqAnd will be Δ u_sd、Δu_sqCorresponding compensation gives u_sdc、u_sqcTo obtain a compensated d-axis voltage component u_sdAnd q-axis voltage component u_sq；

Obtaining a rotor field position angle theta of the AC machine_rAnd according to theta_rWill u_sd、u_sqConverting the dq two-phase rotating coordinate system into an alpha beta two-phase static coordinate system to obtain an alpha axis voltage component u_sαBeta axis voltage component u_sβ；

Will u_sα、u_sβAnd after Space Vector Pulse Width Modulation (SVPWM), controlling the on-state of a switch in an inverter connected with the alternating current motor so as to realize closed-loop control on the torque of the alternating current motor in a linear region.

Preferably, the obtaining of the rotor magnetic field position angle θ of the alternating current motor_rThe process specifically comprises the following steps:

according to a predetermined integral formula theta_r＝∫(P_nω_m+ω_s1) dt, calculating the rotor field position angle theta of the AC machine_rWherein P is_nIs the number of pole pairs, omega_mIs the mechanical angular velocity, omega_s1Is the slip angular velocity.

Preferably, the obtaining of the rotor magnetic field position angle θ of the alternating current motor_rThe process specifically comprises the following steps:

obtaining a rotor magnetic field position angle theta by utilizing a preset observation model of flux linkage torque of the alternating current motor_r；

The process of acquiring the torque of the alternating current motor is specifically as follows:

using the observation model to obtainTorque T of the AC motor_e。

Preferably, the observation model is in particular a voltage model.

Preferably, the step of performing proportional-integral PI closed-loop control on the acquired torque of the ac motor to obtain a voltage vector correction angle of the ac motor, compensating the voltage vector correction angle to a coordinate system transformation angle in the vector control system, and controlling the torque according to the fixed output of two PI controllers in an overmodulation region and the compensated coordinate system transformation angle in the vector control system specifically includes:

will T_eWith a given torque T_e ^*Making a difference, and regulating the difference value by PI to output a voltage vector correction angle delta theta of the alternating current motor_u；

Will delta theta_uAnd theta_rSumming to obtain a coordinate system transformation angle theta' corresponding to the overmodulation region of the vector control system, and under the premise that two PI controllers in the vector control system output fixedly, u is transformed according to theta_sd、u_sqConverting the dq two-phase rotating coordinate system into an alpha beta two-phase static coordinate system to obtain an alpha-axis voltage component u 'corresponding to the overmodulation region'_sαAnd beta-axis voltage component u'_sβ；

U's'_sα、u′_sβAnd controlling the on state of a switch in the inverter after SVPWM modulation so as to realize the control of the torque in an overmodulation region.

Preferably, the difference is output to the voltage vector correction angle delta theta of the alternating current motor through PI regulation_uAfter that, the value of delta theta is adjusted_uAnd theta_rBefore summing, the method for controlling the torque of the alternating current motor further comprises the following steps:

according to the preset amplitude value pair Delta theta_uAnd carrying out amplitude limiting treatment to realize anti-overturn protection of the alternating current motor.

Preferably, the value Δ θ is set according to a preset clipping amplitude_uThe process of performing the amplitude limiting processing specifically includes:

according to

For Δ θ_uPerforming a slicing process in which k_TAs an angle adjustment factor, i_sdEFor the exciting current component under rated conditions, i_sqEIs the torque current component under the rated working condition, sigma is the leakage inductance coefficient,

L_ris the rotor inductance, L_sIs a stator inductance, L_mIs the mutual inductance of the rotor inductance and the stator inductance.

Preferably, Δ θ is set when the control manner corresponding to the overmodulation region is transited to the control manner corresponding to the linear region_uAnd adjusting to zero according to a preset slope.

In order to solve the above technical problem, the present invention further provides an ac motor torque control system based on asynchronous modulation, including:

the comparison module is used for calculating the current corresponding modulation ratio of the alternating current motor and comparing the modulation ratio M with a preset hysteresis lower limit M0 and a preset hysteresis upper limit M1 respectively;

the linear region control module is used for adopting a vector control system based on rotor magnetic field orientation to control the torque of the alternating current motor in a linear region closed loop mode when M is less than M0;

the overmodulation region control module is used for carrying out proportional integral PI closed-loop control on the acquired torque of the alternating current motor when M is larger than M1 to obtain a voltage vector correction angle of the alternating current motor, compensating the voltage vector correction angle to a coordinate system transformation angle in the vector control system, and controlling the torque according to fixed output of two PI controllers in an overmodulation region and the compensated coordinate system transformation angle in the vector control system;

and the hysteresis zone control module is used for controlling the torque according to the control mode corresponding to the last comparison result when M0 is more than or equal to M1.

The invention provides an alternating current motor torque control method based on asynchronous modulation, which comprises the following steps: calculating a current corresponding modulation ratio of the alternating current motor, and respectively comparing the modulation ratio M with a preset hysteresis lower limit M0 and a preset hysteresis upper limit M1; when M is less than M0, a vector control system based on rotor magnetic field orientation is adopted to control the torque of the alternating current motor in a linear region closed loop mode; when M is larger than M1, the obtained torque of the alternating current motor is subjected to proportional-integral PI closed-loop control to obtain a voltage vector correction angle of the alternating current motor, the voltage vector correction angle is compensated to a coordinate system transformation angle in a vector control system, and the torque is controlled according to the fixed output of two PI controllers in an overmodulation region and the compensated coordinate system transformation angle in the vector control system; and when M0 is more than or equal to M1, controlling the torque according to the control mode corresponding to the last comparison result.

Compared with the alternating current motor torque control method in the prior art, the method has the advantages that the torque of the alternating current motor is controlled only in a linear region by adopting a vector control system based on rotor magnetic field orientation, namely two currents under a dq two-phase rotating coordinate system are regulated one by adopting two PI controllers; in the overmodulation region, on one hand, the torque of the alternating current motor is subjected to PI closed-loop control to obtain a voltage vector correction angle of the alternating current motor, and on the other hand, the output of two PI controllers in a vector control system is fixed; and then compensating the voltage vector correction angle to a coordinate system transformation angle in a vector control system, thereby realizing the purpose of jointly controlling the torque of the alternating current motor by utilizing the vector control system with fixed output and the introduced torque closed-loop regulation. Therefore, the method does not adopt PI regulation of two currents, but adopts PI regulation of one torque, so that no coupling exists; in addition, the PI closed-loop control of the torque directly controls the torque by dynamically adjusting the voltage vector angle of the alternating current motor, the torque is accurately adjusted, the dynamic property is good, and therefore the reliability and the stability of the system are improved.

The invention also provides an alternating current motor torque control system based on asynchronous modulation, and the alternating current motor torque control system has the same beneficial effects as the torque control method.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed in the prior art and the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without creative efforts.

FIG. 1 is a flow chart of an AC motor torque control method based on asynchronous modulation according to the present invention;

FIG. 2 is a schematic diagram of a linear AC motor torque control method according to the present invention;

FIG. 3 is a schematic diagram of a method of overmodulation region AC motor torque control according to the present invention;

fig. 4 is a schematic structural diagram of an ac motor torque control system based on asynchronous modulation according to the present invention.

Detailed Description

The core of the invention is to provide an AC motor torque control method and system based on asynchronous modulation, which does not adopt PI regulation of two currents but adopts PI regulation of one torque, so that no coupling exists; in addition, the PI closed-loop control of the torque directly controls the torque by dynamically adjusting the voltage vector angle of the alternating current motor, the torque is accurately adjusted, the dynamic property is good, and therefore the reliability and the stability of the system are improved.

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Referring to fig. 1, fig. 1 is a flowchart of an ac motor torque control method based on asynchronous modulation according to the present invention.

The alternating current motor torque control method comprises the following steps:

step S1: calculating a current corresponding modulation ratio of the alternating current motor, and respectively comparing the modulation ratio M with a preset hysteresis lower limit M0 and a preset hysteresis upper limit M1;

it should be noted that the preset in the present application is set in advance, and only needs to be set once, and the preset does not need to be reset unless modified according to actual conditions.

Specifically, it is known that the modulation ratio M ∈ (0.907,1) of the overmodulation region is smaller than that of the overmodulation region, and based on this, the present application sets upper and lower limits of the hysteresis loop in advance according to the modulation ratio range of the overmodulation region to distinguish the linear region from the overmodulation region, where the upper limit of the hysteresis loop is greater than and close to 0.907 and the lower limit of the hysteresis loop is less than and close to 0.907 (reasonably set). That is, when the modulation ratio corresponding to the ac motor is greater than the upper limit of the hysteresis loop, the modulation mode in which the ac motor is located is the overmodulation region mode; when the modulation ratio corresponding to the alternating current motor is smaller than the lower limit of the hysteresis loop, the modulation mode of the alternating current motor is a linear region mode; when the modulation ratio corresponding to the alternating current motor is within the range of the upper limit and the lower limit of the hysteresis loop, the alternating current motor can be regarded as being in the transition period of switching the two modulation modes.

Therefore, in the present application, a current modulation ratio corresponding to the ac motor is first calculated, and the current modulation ratio is compared with the set lower hysteresis limit and the set upper hysteresis limit (hereinafter, M1 represents the upper hysteresis limit, and M0 represents the lower hysteresis limit), so as to determine the current modulation mode of the ac motor.

Step S2: when M is less than M0, a vector control system based on rotor magnetic field orientation is adopted to control the torque of the alternating current motor in a linear region closed loop mode;

it is understood that the steps S2, S3 and S4 are not performed sequentially, but are performed in three parallel steps, and one of the steps is determined to be performed according to the comparison result of the step S1.

Specifically, when M is less than M0, it is indicated that the modulation mode in which the ac motor is currently located is a linear region mode, the torque of the ac motor is closed-loop controlled according to a vector control system based on rotor magnetic field orientation, that is, the excitation current and the torque current of the ac motor in a two-phase rotating coordinate system are closed-loop controlled one by using two PI controllers, and the torque of the ac motor is further controlled.

Step S3: when M is larger than M1, the obtained torque of the alternating current motor is subjected to proportional-integral PI closed-loop control to obtain a voltage vector correction angle of the alternating current motor, the voltage vector correction angle is compensated to a coordinate system transformation angle in a vector control system, and the torque is controlled according to the fixed output of two PI controllers in an overmodulation region and the compensated coordinate system transformation angle in the vector control system;

specifically, when M > M1, it is stated that the modulation mode in which the ac motor is currently located is an overmodulation region mode, and since the overmodulation region is output nonlinearly and the harmonic is large, the control mode in the linear region cannot control the torque of the ac motor (overshoot phenomenon and coupling phenomenon exist), so the present application specifically sets the control mode for the overmodulation region:

1) the output of two PI controllers in the vector control system is fixed, namely the two PI controllers do not calculate, but the output value of the two PI controllers is kept unchanged, the open-loop voltage setting is similar, and the stability is good. Therefore, in the overmodulation region, the two PI controllers in the vector control system do not play a role in regulation any more, and the phenomenon of overshooting and the phenomenon of serious coupling do not occur.

2) The method introduces torque closed-loop regulation (known through a large number of simulations and experiments, when the voltage vector angle of the alternating current motor changes, the current of the alternating current motor changes along with the change of the voltage vector angle, and the voltage vector angle of the alternating current motor has direct influence on the torque of the alternating current motor, so that the torque is directly regulated by adopting the torque closed-loop regulation), specifically, firstly, the given torque and the obtained torque of the alternating current motor are subjected to difference, and the difference is regulated through PI (proportional integral) to obtain a voltage vector correction angle of the alternating current motor; and then adding the voltage vector correction angle to the original coordinate system transformation angle (transformation angle between the two-phase rotating coordinate system and the two-phase stationary coordinate system, namely the rotor magnetic field position angle) in the vector control system, and taking the sum of the voltage vector correction angle and the original coordinate system transformation angle as the coordinate system transformation angle corresponding to the overmodulation region (it should be noted that the voltage vector correction angle is only used for calculation of coordinate system transformation in the vector control system, and the rotor magnetic field position angle is not modified essentially).

3) On the basis that the outputs of two PI controllers in a vector control system are fixed, the torque of the alternating current motor is controlled together by the vector control system with fixed output and the introduced torque closed-loop regulation. Therefore, the control function is really the introduced torque closed-loop regulation, and the torque closed-loop regulation is that the torque is directly controlled by dynamically regulating the voltage vector angle of the alternating current motor, so the torque regulation is accurate and the dynamic property is good; in addition, only one torque PI regulation is adopted, so that no coupling exists, and the regulation is easy.

In summary, two modulation modes are switched: from the linear region to the overmodulation region: the outputs of two PI controllers in the vector control system are kept in the current state, the torque is input in a closed loop mode, and the system has no impact; from the overmodulation region to the linear region: the vector control system is put into operation, and the torque is cut off in a closed loop mode (the voltage vector correction angle tends to 0).

Step S4: and when M0 is more than or equal to M1, controlling the torque according to the control mode corresponding to the last comparison result.

Specifically, when M0 is more than or equal to M1, the alternating current motor is in a transition period of switching two modulation modes, and the torque of the alternating current motor is controlled according to a control mode corresponding to a last comparison result, namely the last comparison result is M > M1, and the torque of the alternating current motor is controlled according to the control mode corresponding to an overmodulation region; if the last comparison result is M < M0, the torque of the ac motor is controlled in a control manner corresponding to the linear region.

The invention provides an alternating current motor torque control method based on asynchronous modulation, which comprises the following steps: calculating a current corresponding modulation ratio of the alternating current motor, and respectively comparing the modulation ratio M with a preset hysteresis lower limit M0 and a preset hysteresis upper limit M1; when M is less than M0, a vector control system based on rotor magnetic field orientation is adopted to control the torque of the alternating current motor in a linear region closed loop mode; when M is larger than M1, the obtained torque of the alternating current motor is subjected to proportional-integral PI closed-loop control to obtain a voltage vector correction angle of the alternating current motor, the voltage vector correction angle is compensated to a coordinate system transformation angle in a vector control system, and the torque is controlled according to the fixed output of two PI controllers in an overmodulation region and the compensated coordinate system transformation angle in the vector control system; and when M0 is more than or equal to M1, controlling the torque according to the control mode corresponding to the last comparison result.

Compared with the alternating current motor torque control method in the prior art, the method has the advantages that the torque of the alternating current motor is controlled only in a linear region by adopting a vector control system based on rotor magnetic field orientation, namely two currents under a dq two-phase rotating coordinate system are regulated one by adopting two PI controllers; in the overmodulation region, on one hand, the torque of the alternating current motor is subjected to PI closed-loop control to obtain a voltage vector correction angle of the alternating current motor, and on the other hand, the output of two PI controllers in a vector control system is fixed; and then compensating the voltage vector correction angle to a coordinate system transformation angle in a vector control system, thereby realizing the purpose of jointly controlling the torque of the alternating current motor by utilizing the vector control system with fixed output and the introduced torque closed-loop regulation. Therefore, the method does not adopt PI regulation of two currents, but adopts PI regulation of one torque, so that no coupling exists; in addition, the PI closed-loop control of the torque directly controls the torque by dynamically adjusting the voltage vector angle of the alternating current motor, the torque is accurately adjusted, the dynamic property is good, and therefore the reliability and the stability of the system are improved.

On the basis of the above-described embodiment:

as a preferred embodiment, the process of closed-loop controlling the torque of the ac motor in the linear region by using a vector control system based on the orientation of the rotor magnetic field is specifically as follows:

obtaining the exciting current i of the AC motor under the dq two-phase rotating coordinate system_sdAnd torque current i_sqAnd according to a given excitation current

And given torque current

Calculating the original d-axis voltage component u_sdcAnd the original q-axis voltage component u_sqcAnd will be

Correspond to i_sd、i_sqMaking a difference;

correspondingly outputting the two difference values by adjusting the d-axis voltage compensation quantity delta u through two PI controllers_sdAnd q-axis electricityPressure compensation amount Deltau_sqAnd will be Δ u_sd、Δu_sqCorresponding compensation gives u_sdc、u_sqcTo obtain a compensated d-axis voltage component u_sdAnd q-axis voltage component u_sq；

Obtaining rotor magnetic field position angle theta of alternating current motor_rAnd according to theta_rWill u_sd、u_sqConverting the dq two-phase rotating coordinate system into an alpha beta two-phase static coordinate system to obtain an alpha axis voltage component u_sαBeta axis voltage component u_sβ；

Will u_sα、u_sβAfter Space Vector Pulse Width Modulation (SVPWM), the on-state of a switch in an inverter connected with the alternating current motor is controlled, so that the torque of the alternating current motor is controlled in a closed loop manner in a linear region.

Specifically, referring to fig. 2, fig. 2 is a schematic diagram of a torque control method for a linear ac motor according to the present invention, and the control principle is as follows:

1) obtaining the exciting current i of the alternating current motor M under the dq two-phase rotating coordinate system_sdAnd torque current i_sq(process: collecting three-phase AC current input by stator of AC motor M by current sensor, converting three-phase AC current into two-phase AC current input by two-phase windings which are mutually vertical according to principle of equal magnetomotive force, i.e. converting from alpha bc three-phase stationary coordinate system to alpha beta two-phase stationary coordinate system, converting two-phase AC current into two DC currents according to synchronous rotating coordinate conversion formula, i.e. converting from alpha beta two-phase stationary coordinate system to dq two-phase rotating coordinate system, so as to obtain exciting current i of AC motor M_sdAnd torque current i_sq)；

3) Considering that the proportion of the coupling voltage between the d axis and the q axis in the output voltage is larger and larger along with the increase of the rotating speed of the alternating current motor M, and the system performance is seriously influenced, therefore, the feedback control method is adopted in the application to reduce the pressure of closed-loop control:

in the feedback aspect, the exciting current is given

Given torque current

Correspond to i_sd、i_sqMaking a difference, correspondingly adjusting and outputting the d-axis voltage compensation quantity delta u by the two difference values through two PI controllers_sdAnd q-axis voltage compensation amount Deltau_sq(ii) a Aspect of feed forward, according to

Calculating the original d-axis voltage component u_sdcAnd the original q-axis voltage component u_sqc(ii) a Then the delta u is_sd、Δu_sqCorresponding compensation gives u_sdc、u_sqcTo obtain a compensated d-axis voltage component u_sdAnd q-axis voltage component u_sq；

4) Obtaining rotor magnetic field position angle theta of alternating current motor M_rI.e. the transformation angle of the dq two-phase rotating coordinate system-alpha beta two-phase stationary coordinate system of the vector control system, and then according to theta_rWill u_sd、u_sqConverting the dq two-phase rotating coordinate system into an alpha beta two-phase static coordinate system to obtain an alpha axis voltage component u_sαBeta axis voltage component u_sβ(ii) a Finally u is to_sα、u_sβAfter being modulated by SVPWM (Space Vector pulse width Modulation), the switching-on state of a switch in an inverter connected to the ac motor M is controlled, so that the current input to the ac motor M is adjusted, and the torque of the ac motor M is controlled in a linear region closed loop.

As a preferred embodiment, the rotor magnetic field position angle theta of the alternating current motor is obtained_rThe process specifically comprises the following steps:

according to a predetermined integral formula theta_r＝∫(P_nω_m+ω_s1) dt, calculating rotor field position angle theta of AC machine_rWherein P is_nIs the number of pole pairs, omega_mIs the mechanical angular velocity, omega_s1Is the slip angular velocity.

Further, the rotor field position angle θ of the AC motor_rThe method of obtaining (A) may be an integration method, i.e. according to the integral formula theta_r＝∫(P_nω_m+ω_s1) dt, calculating θ_r。

As a preferred embodiment, the rotor magnetic field position angle theta of the alternating current motor is obtained_rThe process specifically comprises the following steps:

obtaining the position angle theta of the rotor magnetic field by utilizing a preset observation model of flux linkage torque of the alternating current motor_r；

The process of acquiring the torque of the ac motor is specifically as follows:

obtaining the torque T of the AC motor by using the observation model_e。

Further, the rotor field position angle θ of the AC motor_rThe method of obtaining (1) can also select flux linkage observation method, that is, observation model using flux linkage torque of AC motor (input variable: mechanical angular velocity ω of AC motor)_mInput current i_s) Obtaining theta of the alternating current motor_rRotor flux linkage vector

And torque T_e(output variable). Wherein, theta_rAs rotor flux linkage vector

The phase of (c).

Based on the method, the application can select any method to obtain theta_rTo facilitate distinguishing the two methods, the present application uses θ as the rotor magnetic field position angle obtained by the flux linkage observation method_r1Showing the rotor field position angle theta obtained by the integration method_r2And (4) showing.

As a preferred embodiment, the observation model is embodied as a voltage model.

Specifically, the voltage model is selected for the observation model in the application, and the voltage model is simple and does not depend on the rotating speed and the rotor resistance parameter of the alternating current motor, so that the alternating current motor can accurately run at the middle-high speed stage when the rotating speed of the alternating current motor reaches the middle-high speed stage.

As a preferred embodiment, the acquired torque of the ac motor is subjected to proportional-integral PI closed-loop control to obtain a voltage vector correction angle of the ac motor, the voltage vector correction angle is compensated to a coordinate system transformation angle in a vector control system, and the process of controlling the torque according to the fixed output of two PI controllers in an overmodulation region and the compensated coordinate system transformation angle in the vector control system is specifically as follows:

will T_eWith a given torque T_e ^*Making difference, regulating the difference value by PI and outputting voltage vector correction angle delta theta of AC motor_u；

Will delta theta_uAnd theta_rSumming to obtain a coordinate system transformation angle theta' corresponding to the overmodulation region of the vector control system, and under the premise that two PI controllers in the vector control system output fixedly, u is transformed according to the theta_sd、u_sqConverting the dq two-phase rotating coordinate system into an alpha beta two-phase static coordinate system to obtain an alpha-axis voltage component u 'corresponding to the overmodulation region'_sαAnd beta-axis voltage component u'_sβ；

U's'_sα、u′_sβAnd after SVPWM modulation, controlling the on state of a switch in the inverter so as to realize the control of the torque in an overmodulation region.

Specifically, referring to fig. 3, fig. 3 is a schematic diagram of a method for controlling a torque of an ac motor in an overmodulation region according to the present invention, and the control principle is as follows:

1) in a vector control system, two PI controllers do not calculate, but the output values thereof remain unchanged, and the voltage component u_sd、u_sqCalculating and voltage compensating quantity delta u from feedforward_sd、Δu_sqThe sum of the fixed values is obtained, the voltage is given similarly to open loop voltage, and the stability is good;

2) closed-loop regulation of input torque, i.e. torque T obtained by observation model_eWith a given torque T_e ^*Making a difference, and regulating the difference value by PI to output a voltage vector correction angle delta theta of the alternating current motor M_uThen, delta theta_uAnd theta_rSumming to obtain a coordinate system transformation angle theta' corresponding to the overmodulation region of the vector control system, namely a transformation angle of a dq two-phase rotating coordinate system-alpha beta two-phase static coordinate system at the moment;

3) according to theta' will u_sd、u_sqConverting the dq two-phase rotating coordinate system into an alpha beta two-phase static coordinate system to obtain an alpha-axis voltage component u 'corresponding to the overmodulation region'_sαAnd beta-axis voltage component u'_sβThen u'_sα、u′_sβAfter SVPWM modulation, the on-state of a switch in the inverter is controlled, so that the current input to the alternating current motor M is adjusted, and the torque of the alternating current motor M is controlled in an overmodulation region.

As a preferred embodiment, the voltage vector correction angle delta theta of the alternating current motor is output after the difference value is subjected to PI regulation_uAfter that, the value of delta theta is adjusted_uAnd theta_rBefore summing, the method for controlling the torque of the alternating current motor further comprises the following steps:

according to the preset amplitude value pair Delta theta_uAnd carrying out amplitude limiting treatment to realize anti-overturn protection of the alternating current motor.

Further, considering that the voltage vector angle can enter a subversion area when exceeding the limit and PI regulation of torque can be maladjusted when exceeding the limit seriously, the voltage vector correction angle delta theta of the alternating current motor is obtained by the method_uThen, first, the set clipping amplitude (including the upper limit amplitude and the lower limit amplitude) is applied to Δ θ_uIs subjected to a clipping process, i.e. delta theta_uDoes not exceed the set upper limit amplitude, Δ θ_uIs not lower than the set lower limit amplitude, and then the limited delta theta is used_uAnd theta_rAnd summing is carried out, so that the anti-overturn protection of the alternating current motor is realized, and the control safety and reliability of the alternating current motor are improved.

In a preferred embodiment, Δ θ is determined according to a preset clipping amplitude value_uThe process of performing the amplitude limiting processing specifically includes:

according to

For Δ θ_uPerforming a slicing process in which k_TAs an angle adjustment factor, i_sdEFor the exciting current component under rated conditions, i_sqEIs the torque current component under the rated working condition, sigma is the leakage inductance coefficient,

L_ris the rotor inductance, L_sIs a stator inductance, L_mIs the mutual inductance of the rotor inductance and the stator inductance.

Specifically, Δ θ_uThe upper limit amplitude of (2) is:

a lower limit amplitude of

Wherein k is_TThe value is preferably 0.1-0.2.

As a preferable embodiment, Δ θ is set when the control manner corresponding to the overmodulation region is transited to the control manner corresponding to the linear region_uAnd adjusting to zero according to a preset slope.

Further, when the control mode corresponding to the overmodulation region is transited to the control mode corresponding to the linear region, the transition process of the coordinate system transformation angle of the vector control system is as follows: θ' → θ_rθ' ═ θ_r+Δθ_uSo the actual transition process of the coordinate system transformation angle is: delta theta_u→ 0. To prevent voltage vector angle jump, which can cause system overcurrent fault, Δ θ_uCannot be set to 0 immediately and should be adjusted to 0 with a certain slope.

For example, Δ θ_uThe allowable variation amount in each switching cycle of the inverter is d, and d can be equal to 0.01 degrees, and the following judgment is made:

Δθ_u＞d,Δθ_u(n)＝Δθ_u(n-1)-d；

Δθ_u＜-d,Δθ_u(n)＝Δθ_u(n-1)+d；

-d≤Δθ_u≤d,Δθ_u(n)＝0。

referring to fig. 4, fig. 4 is a schematic structural diagram of an ac motor torque control system based on asynchronous modulation according to the present invention.

The alternating current motor torque control system includes:

the comparison module 1 is used for calculating a modulation ratio currently corresponding to the alternating current motor and comparing the modulation ratio M with a preset hysteresis lower limit M0 and a preset hysteresis upper limit M1 respectively;

the linear region control module 2 is used for adopting a vector control system based on rotor magnetic field orientation to control the torque of the alternating current motor in a linear region closed loop mode when M is less than M0;

the overmodulation region control module 3 is used for performing proportional integral PI closed-loop control on the acquired torque of the alternating current motor to obtain a voltage vector correction angle of the alternating current motor when M is larger than M1, compensating the voltage vector correction angle to a coordinate system transformation angle in a vector control system, and controlling the torque according to fixed output of two PI controllers in an overmodulation region and the compensated coordinate system transformation angle in the vector control system;

and the hysteresis zone control module 4 is used for controlling the torque according to the control mode corresponding to the last comparison result when M0 is more than or equal to M1.

For the introduction of the torque control system provided in the present application, reference is made to the above method embodiments, and details are not repeated herein.

It should also be noted that, in the present specification, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in a process, method, article, or apparatus that comprises the element.

The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.