A control method and control system of a permanent magnet synchronous motor for vehicle

Abstract

The application provides a control method and a control system of a vehicle permanent magnet synchronous motor. A torque control unit converts a torque instruction input by a vehicle control unit into corresponding stator current instructions; a control mode enabling unit selects and switches corresponding control modes according to a current motor speed, enables an MPC control mode when the motor speed is lower than a base speed point, and enables a PID control mode when the motor speed is higher than the base speed point; an SVPWM modulation unit takes the phase voltage vector calculated by the MPC or PID unit as input, calculates the actual conduction sequence and conduction time of the inverter power tube corresponding to the target voltage, and generates six low-voltage PWM modulation signals to control the on-off of the six power tubes in the inverter; and the motor controller turns on and off the power switch tube of the inverter according to a certain rule under the modulation of the SVPWM modulation unit, and modulates the input DC voltage into a three-phase AC voltage.

Description

Technical Field

[0001] This invention relates to the field of motor control technology, and in particular to a control method and control system for a vehicle permanent magnet synchronous motor. Background Technology

[0002] Permanent magnet synchronous motors (PMSMs) have been widely used in electric drive systems of new energy vehicles due to their advantages such as high efficiency, excellent durability, high torque and power density, and ease of control. During vehicle operation, the PMSM outputs corresponding torque under the command of the motor controller. For torque control of PMSMs, the commonly used algorithm is the vector control algorithm (FOC).

[0003] Compared to the direct torque method, the vector control algorithm does not have excessive torque fluctuations in the low-speed range and is less likely to cause overheating; in addition, it includes a current closed-loop control process, which is less likely to cause overcurrent, and can meet the stable high torque output requirements of automobiles at low speeds and when climbing hills.

[0004] Vector control algorithms transform the three-phase currents of an AC motor using coordinate transformations. The transformation proceeds from a three-phase stationary coordinate system to a two-phase stationary coordinate system and then to a synchronously rotating coordinate system, ultimately yielding two DC components: the direct-axis current component and the quadrature-axis current component. This converts the control of AC quantities into the control of DC quantities. A current closed-loop control structure then enables accurate tracking of the commanded current by the actual current. PID control algorithms are commonly used in engineering for this purpose, and MPC control algorithms are increasingly being adopted in various applications.

[0005] PID control algorithm: The difference between the reference value and the actual value of the AC and DC axis current components of the motor is used as the output. The input voltage component of the motor model is obtained through the PID control unit. Then, the back electromotive force generated by the rotor flux is fed forward and coupled to obtain the final phase voltage input value of the model.

[0006] Finite set MPC control algorithm: Without the assistance of SVPWM modulation algorithm, the optimal voltage vector solution is determined by substituting the voltage vector corresponding to each switching state of the inverter into the cost function, thereby obtaining the most ideal switching state in the current carrier frequency cycle.

[0007] Continuous set MPC control algorithm: Combining modulation algorithms such as SVPWM or SPWM, the optimal voltage vector solution is obtained by finding the minimum point of the cost function within the constraints, and a modulation wave with multiple switching combinations is generated by the PWM modulation module.

[0008] The shortcomings of PID control algorithms are as follows: In engineering applications, the process of modeling the control system is often lacking, and parameter tuning mainly adopts qualitative adjustment, making it difficult to achieve precise quantification; for time-varying systems, PID parameters need to be adjusted in real time, which increases the time cost of parameter tuning in the early stage.

[0009] The drawbacks of the MPC control algorithm are as follows: While the MPC control algorithm can achieve precise control based on the motor model, its computational burden is too large. When the motor travels to the high-speed range, the carrier frequency period becomes smaller, making it difficult for the system to allocate sufficient resources for the MPC control algorithm.

[0010] Therefore, for the control of automotive permanent magnet synchronous motors, a control strategy is needed that can overcome the shortcomings of PID control algorithms and MPC control algorithms and combine the advantages of both. Summary of the Invention

[0011] To address the above problems, this invention proposes a control method and control system for a vehicle permanent magnet synchronous motor.

[0012] This invention provides a control method for a permanent magnet synchronous motor for vehicles. The control method switches between different control methods based on the relative relationship between the actual speed of the motor and the base speed point. When the speed is lower than the base speed point, the MPC control algorithm is used, and when the speed is higher than the base speed point, the PID control algorithm is used. The MPC control algorithm and the PID control algorithm use the current command output by the torque control unit as a reference quantity to perform closed-loop current control.

[0013] Furthermore, the MPC control algorithm derives and calculates the state variables and voltage vector results for the next few control cycles based on the measured state variable values ​​of the motor at the current moment through state space equations; it establishes a cost function for the state variable error and phase voltage fluctuation, and after one calculation, obtains the phase voltage vector corresponding to the optimal control accuracy.

[0014] Furthermore, the specific steps for implementing the MPC control algorithm are as follows:

[0015] (1) Sampling of three-phase current and rotor position;

[0016] (2) Coordinate transformation is used to obtain the d / q axis current, and the resolver calculation is used to obtain the angular velocity;

[0017] (3) Calculate the d / q axis voltage value at the current moment based on the voltage model;

[0018] (4) Obtain the optimal value of the d / q axis voltage change at the next moment according to the MPC control algorithm;

[0019] (5) Output the d / q axis voltage value at the next moment.

[0020] Furthermore, the state-space equation of the MPC control algorithm is:

[0021]

[0022] Where id and iq are the dq-axis currents of the motor, respectively; Ld and Lq are the dq-axis inductances of the motor, respectively; w is the motor speed, and wi is the motor rotation speed. q It is the product of motor speed and q-axis current, wi d It is the product of motor speed and d-axis current; R is the internal resistance of the motor coil; λ is the motor rotor flux linkage; ud and uq are the motor d- and q-axis voltages, respectively.

[0023] Furthermore, the cost function of the MPC control algorithm is:

[0024]

[0025] Where Np is the number of prediction steps, Nu is the number of predicted control steps, Q is the weight of the system output change, and R is the weight of the system control input change; Id / q is the actual current vector under the dq axis of the motor, Id / q,ref is the reference current vector under the dq axis of the motor, Δud / q is the change in the voltage vector under the dq axis of the motor, Id / q,base is the rated current value, and ud / q,base is the rated voltage value.

[0026] Furthermore, the PID control algorithm frequently and qualitatively adjusts the phase voltage vector based on the actual error of the current in each control cycle, so that the output current of the motor gradually approaches the reference value.

[0027] This invention provides a control system for a vehicle-mounted permanent magnet synchronous motor. The control system includes a motor power drive section and a motor control logic section. The motor power drive section includes a DC bus power supply, a motor controller, and a permanent magnet synchronous motor. The motor control logic section includes a torque control unit, a control mode enable unit, an MPC control unit, a PID control unit, and an SVPWM modulation unit. The torque control unit converts the torque command input from the vehicle control unit into a corresponding stator current command. The control mode enable unit selects and switches the corresponding control mode according to the current motor speed. When the motor speed is below the base speed, this unit enables the MPC control mode; when the motor speed is above the base speed, this unit enables the MPC control mode. The unit enables PID control mode; MPC control mode and PID control mode use the current command output by the torque control unit as a reference quantity to perform closed-loop current control; the SVPWM modulation unit uses the phase voltage vector calculated by the MPC or PID unit as input, calculates the actual turn-on sequence and turn-on time of the inverter power transistors corresponding to the target voltage, and generates 6-channel PWM low-voltage modulation signals to control the on and off of the 6 power transistors in the inverter; under the modulation action of the SVPWM modulation unit, the motor controller turns on and off the power switching transistors of the inverter, modulates the input DC voltage into a three-phase AC voltage, applies it to the three-phase input terminal of the permanent magnet synchronous motor, and excites it to generate the expected three-phase current.

[0028] Furthermore, the motor control logic section also includes a field weakening current calculation unit, which is used to obtain the specific offset of the d-axis current as the speed or torque increases within the field weakening range.

[0029] The present invention provides an electronic device, including a memory and a processor. The memory stores a computer program, and the processor executes the computer program to implement the steps of the permanent magnet synchronous motor control method of the present invention.

[0030] The present invention provides a computer-readable storage medium for storing computer instructions, which, when executed by a processor, implement the steps of the permanent magnet synchronous motor control method described in the present invention.

[0031] The beneficial effects of this invention are as follows:

[0032] (1) This invention combines the technical advantages of MPC control algorithm and PID control algorithm to achieve high-precision and flexible control functions. Through this invention, the MPC algorithm can be applied in the constant torque region of the motor to reduce the overshoot of the controlled object, shorten the system response time, and achieve precise control of the motor output torque. When the motor speed increases and enters the constant power region, the system will switch to the PID control algorithm, reducing the computational load of the system while ensuring control accuracy.

[0033] (2) In establishing the state vector of the MPC algorithm, this invention differs from previous literature and patents that directly select the dq-axis current or stator flux linkage and output torque. To ensure that the motor model can form a standard state-space equation after discretization and derivation, this invention establishes a state-space equation composed of id, iq, w, and wi. d wi q The resulting 5-dimensional state vector reduces the workload of formula processing in subsequent prediction calculations.

[0034] (3) In establishing the cost function, this invention adds a dimensionality reduction process for the state vector, selecting only the id and iq dimensions for calculation, and simplifies the cost function to a quadratic programming form about the dq-axis current error and the dq-axis voltage increment. In addition, this invention standardizes the two physical quantities, current and voltage, so that the two physical quantities can be compared on the same order of magnitude, thus omitting the selection process of weighting coefficients. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the control system for a permanent magnet synchronous motor used in automobiles.

[0036] Figure 2 This is an implementation scheme for the MPC control algorithm. Detailed Implementation

[0037] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] Example 1.

[0039] 1. A control method for a permanent magnet synchronous motor for vehicles, which integrates the technical advantages of MPC control algorithm and PID control algorithm to achieve stable and precise control of the motor. The control strategy switches between control methods based on the relative relationship between the current actual motor speed and the base speed point. When the speed is below the base speed point (i.e., in the constant torque region), the MPC control algorithm is used; when the speed is above the base speed point (i.e., in the constant power region), the PID control algorithm is used. Both the MPC and PID control algorithms use the current command output by the torque control unit as a reference quantity for closed-loop current control.

[0040] In the low-speed range, the electromagnetic characteristics of the motor exhibit a highly linear relationship, allowing for accurate modeling. The MPC control algorithm based on this model possesses sufficient control precision. In the high-speed range, due to the magnetic saturation and cross-coupling phenomena in the stator core and the complex armature reaction of the stator coils, the entire system exhibits a nonlinear relationship, making it difficult to establish an accurate and real-time mathematical model. The PID algorithm can eliminate the modeling step, significantly reducing development time and costs while meeting control requirements.

[0041] Example 2.

[0042] A control system for a vehicle-mounted permanent magnet synchronous motor, the schematic diagram of which is shown below. Figure 1 As shown.

[0043] exist Figure 1The technical solution comprises two parts: a motor power drive section and a motor control logic section. The motor power drive section includes a DC bus power supply, a motor controller, and a permanent magnet synchronous motor. The motor control logic section includes a torque control unit, a control mode enable unit, an MPC control unit, a PID control unit, a field weakening current calculation unit, and an SVPWM modulation unit. The torque control unit converts the torque command input from the vehicle control unit into a corresponding stator current command. The control mode enable unit selects and switches the appropriate control mode based on the current motor speed. When the motor speed is below the base speed, this unit enables the MPC control mode; when the motor speed is above the base speed, this unit enables the PID control mode. The MPC and PID control modes use the current command output by the torque control unit as a reference to perform closed-loop current control. The SVPWM modulation unit uses the phase voltage vector calculated by the MPC or PID unit as input to calculate the actual conduction sequence and conduction time of the inverter power transistors corresponding to the target voltage, and generates 6 PWM low-voltage modulation signals to control the on / off state of the 6 power transistors in the inverter. Under the modulation action of the internal control unit, the motor controller turns on and off the inverter power switching transistors according to a certain pattern, modulating the input DC voltage into a three-phase AC voltage, which is applied to the three-phase input terminals of the permanent magnet synchronous motor to excite it to generate the expected three-phase current.

[0044] Specifically:

[0045] (1) The motor power drive section includes a DC bus power supply, a motor controller, and a permanent magnet synchronous motor. The DC bus power supply provides input power to the electric drive system; under the modulation of the internal control unit, the motor controller turns on and off the power switch of the inverter according to a certain rule, modulates the input DC voltage into a three-phase AC voltage, and applies it to the three-phase input terminal of the permanent magnet synchronous motor to excite it to generate the expected three-phase current.

[0046] (2) The motor control logic section includes a torque control unit, an MPC control unit, a PID control unit, a field weakening current calculation unit, a control mode enable unit, and an SVPWM modulation unit.

[0047] (3) The function of the torque control unit is to convert the torque command input by the vehicle control unit into the corresponding stator current command. Commonly used methods include MTPA method, negative id field weakening current correction method, and table lookup method.

[0048] (4) The function of the MPC control unit is to perform closed-loop current control using the current command output by the torque control unit as a reference. Based on the measured values ​​of the motor's current state variables, the state variables and voltage vector results for the next few control cycles are derived and calculated through a mathematical model. A cost function for the state variable error and phase voltage fluctuation is established, and after one calculation, the phase voltage vector corresponding to the optimal control accuracy is obtained.

[0049] (5) The function of the PID control unit is to perform closed-loop current control based on the current command output by the torque control unit. It frequently makes qualitative adjustments to the phase voltage vector according to the actual error of the current in each control cycle, so that the output current of the motor gradually approaches the reference value and improves the control accuracy of the system.

[0050] (6) The function of the field weakening current calculation unit is to obtain the specific offset of the d-axis current as the speed or torque increases within the field weakening range of the motor.

[0051] (7) The function of the control mode enable unit is to select and switch the corresponding control mode according to the current speed of the motor. When the motor speed is lower than the base speed point, that is, in the constant torque range, this unit needs to enable the MPC control mode; when the motor speed is higher than the base speed point, that is, in the constant power range, this unit needs to enable the PID control mode.

[0052] (8) The function of the SVPWM modulation unit is to take the phase voltage vector calculated by the MPC or PID control unit as input, calculate the actual turn-on sequence and turn-on time of the inverter power transistors corresponding to the target voltage, and generate 6 PWM low-voltage modulation signals to control the on and off of the 6 power transistors in the inverter.

[0053] Example 3.

[0054] An implementation scheme for an MPC control algorithm, the process is as follows: Figure 2 As shown, the specific steps are as follows:

[0055] (1) Sampling of three-phase current and rotor position;

[0056] (2) Coordinate transformation is used to obtain the d / q axis current, and the resolver calculation is used to obtain the angular velocity;

[0057] (3) Calculate the d / q axis voltage value at the current moment based on the voltage model;

[0058] (4) Obtain the optimal value of the d / q axis voltage change at the next moment according to the MPC control algorithm;

[0059] (5) Output the d / q axis voltage value at the next moment.

[0060] The state-space equation of the MPC control algorithm is as follows:

[0061]

[0062] Where id and iq are the dq-axis currents of the motor, respectively; Ld and Lq are the dq-axis inductances of the motor, respectively; w is the motor speed, and wi is the motor rotation speed. q It is the product of rotational speed and q-axis current, wi d It is the product of rotational speed and d-axis current; R is the internal resistance of the motor coil; λ is the rotor flux linkage of the motor; ud and uq are the d- and q-axis voltages of the motor, respectively.

[0063] This invention differs from previous methods in literature and patents that directly select the dq-axis current or stator flux linkage and output torque when establishing the state vector of the MPC algorithm. To ensure that the motor model can form a standard state-space equation after discretization and derivation, this invention establishes a state-space equation composed of id, iq, w, and wi. d wi q The resulting 5-dimensional state vector reduces the workload of formula processing in subsequent prediction calculations.

[0064] The cost function of the MPC control algorithm is:

[0065]

[0066] Where Np is the number of prediction steps, Nu is the number of predicted control steps, Q is the weight of the system output change, and R is the weight of the system control input change; Id / q is the actual current vector under the dq axis of the motor, Id / q,ref is the reference current vector under the dq axis of the motor, Δud / q is the change in the voltage vector under the dq axis of the motor, Id / q,base is the rated current value, and ud / q,base is the rated voltage value.

[0067] In establishing the cost function, this invention incorporates a dimensionality reduction process for the state vector, selecting only the id and iq dimensions for calculation. Furthermore, the cost function is simplified to a quadratic programming form relating the dq-axis current error and the dq-axis voltage increment. Additionally, this invention standardizes both current and voltage quantities, enabling comparisons between the two quantities at the same order of magnitude, thus eliminating the need for selecting weighting coefficients.

[0068] Example 4.

[0069] An electronic device includes a memory and a processor, the memory storing a computer program, the processor executing the computer program to implement the steps of the permanent magnet synchronous motor control method of the present invention. A computer-readable storage medium is provided for storing computer instructions, which, when executed by a processor, implement the steps of the permanent magnet synchronous motor control method of the present invention.

Claims

1. A control method of a permanent magnet synchronous motor for a vehicle, characterized by: The control method is to switch the control method according to the relative relationship between the current motor actual speed and the base speed point, when the speed is lower than the base speed point, the MPC control algorithm is used, when the speed is higher than the base speed point, the PID control algorithm is used; the MPC control algorithm and the PID control algorithm take the current instruction of the torque control unit as the reference quantity to carry out the closed loop control of the current; The MPC control algorithm calculates the state variable and voltage vector result in the next several control periods through the state space equation according to the state variable measurement value at the current moment of the motor; a cost function about the state variable error and the phase voltage fluctuation is established, and the phase voltage vector corresponding to the optimal control accuracy is obtained through one calculation; The cost function of the MPC control algorithm is: where N p is the prediction step number, N u is the predicted control step number, Q is the weight of the system output change, R is the weight of the system control input change; I d / q is the actual current vector in the d / q axis of the motor, I d / q,ref is the reference current vector in the d / q axis of the motor, △u d / q is the change in the voltage vector in the d / q axis of the motor, I d / q,base is the current rating, and u d / q,base is the voltage rating.

2. The control method of a permanent magnet synchronous motor for a vehicle according to claim 1, characterized by: The specific steps of the MPC control algorithm are: (1) three-phase current, rotor position sampling; (2) coordinate transformation to obtain d / q axis current, and rotation transformation calculation to obtain angular velocity; (3) calculating the d / q axis voltage value at the current moment according to the voltage model; (4) obtaining the optimal value of the d / q axis voltage change at the next moment according to the MPC control algorithm; (5) outputting the d / q axis voltage value at the next moment.

3. The control method of a permanent magnet synchronous motor for a vehicle according to claim 1, characterized by: The PID control algorithm adjusts the phase voltage vector frequently according to the actual error of the current in each control period, so that the output current of the motor gradually approaches the reference value.

4. A control system for a permanent magnet synchronous motor for a vehicle, characterized by: The control system comprises a motor power driving part and a motor control logic part; the motor power driving part comprises a direct current bus power supply, a motor controller and a permanent magnet synchronous motor; the motor control logic part comprises a torque control unit, a control mode enabling unit, an MPC control unit, a PID control unit and an SVPWM modulation unit; the torque control unit converts the torque instruction input by the vehicle control unit into corresponding stator current instruction; the control mode enabling unit selects the corresponding control mode according to the current speed of the motor, when the motor speed is lower than the base speed point, the unit enables the MPC control mode; when the motor speed is higher than the base speed point, the unit enables the PID control mode; the MPC control mode and the PID control mode take the current instruction output by the torque control unit as the reference quantity to carry out the closed loop control of the current; the SVPWM modulation unit takes the phase voltage vector calculated by the MPC or PID unit as the input, calculates the actual conduction sequence and conduction time of the inverter power tube corresponding to the target voltage, and generates 6-way PWM low voltage modulation signal to control the on-off of the 6-way power tube in the inverter; The motor controller turns on and off the power switch tube of the inverter under the modulation of the SVPWM modulation unit, and modulates the input direct current voltage into three-phase alternating current voltage, which acts on the three-phase input end of the permanent magnet synchronous motor to excite it to generate the expected three-phase current; The MPC control mode calculates the state variable and voltage vector result in the next several control periods through the state space equation according to the state variable measurement value at the current moment of the motor; a cost function about the state variable error and the phase voltage fluctuation is established, and the phase voltage vector corresponding to the optimal control accuracy is obtained through one calculation; The cost function of the MPC control mode is: where N p is the predicted step number, N u is the predicted control step number, Q is the weight of the system output change, R is the weight of the system control input change; I d / q is the actual current vector under the d / q axis of the motor, I d / q,ref is the reference current vector under the d / q axis of the motor, △u d / q is the change of the voltage vector under the d / q axis of the motor, I d / q,base is the current rated value, u d / q,base is the voltage rated value.

5. The control system of a permanent magnet synchronous motor for a vehicle according to claim 4, characterized by: The motor control logic part further comprises a field weakening current calculation unit, configured to obtain a specific offset of the d-axis current corresponding to the motor in the field weakening interval with the increase of the rotating speed or the torque. 6.An electronic device comprising a memory and a processor, the memory storing a computer program, the electronic device characterized by: The processor executes the computer program to realize the steps of the method in any one of claims 1-3.

7. A computer readable storage medium for storing computer instructions, characterized in that: The computer instructions are executed by the processor to realize the steps of the method in any one of claims 1-3.

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