Permanent magnet synchronous motor control method

Abstract

This invention relates to the field of motor control technology and provides a control method for a permanent magnet synchronous motor, comprising the following steps: S1: If the actual speed is less than or equal to the base speed, the MTPA control mode is adopted; if the actual speed is greater than the base speed, the field weakening control mode is adopted and step S2 is executed; S2: The current vector at this moment is obtained, and the absolute value of the combined voltage of the voltage vector corresponding to the current vector is determined to be greater than or equal to the absolute value of the maximum phase voltage; if the absolute value of the combined voltage is less than the absolute value of the maximum phase voltage, step S3 is executed; if the absolute value of the combined voltage is greater than or equal to the absolute value of the maximum phase voltage, step S4 is executed; S3: The field weakening current is adjusted, and the d-axis current is output as a d-axis current command to the current controller; S4: The field weakening current is adjusted, and the d-axis current is output as a d-axis current command to the current controller. This control method simplifies the control process and maintains the stability of the dynamic performance of the control.

Description

Technical Field

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

[0002] With the continuous development of industrial technology, permanent magnet synchronous motors are widely used due to their high efficiency, high power density, and high reliability. Interior permanent magnet synchronous motors (IPMSMs) embed permanent magnets inside the rotor, possessing a robust rotor mechanical structure, making them suitable for high-speed applications such as electric vehicles and air conditioning compressors.

[0003] Based on the operating characteristic curves of permanent magnet synchronous motors, the operating region can be divided into a constant torque region and a constant power region, with the base speed as the dividing line. Typically, in the constant torque region, maximum torque per ampere (MTPA) control is used to minimize the stator current of the motor under the same torque output, thereby reducing losses in both the motor and the inverter. Once the motor reaches its base speed, it cannot continue to accelerate due to limitations imposed by parameters such as the DC bus voltage and the inverter circuit output current. Field weakening control is then employed to reduce the motor's magnetic field and increase its speed without altering the inverter voltage or motor structure.

[0004] Traditional field weakening control uses formulas to calculate the AC and DC axis current commands, relying on the motor's mathematical model and exhibiting poor portability. To improve controller performance and efficiency, new control methods are constantly emerging, such as lookup table methods and gradient descent methods. However, these methods do not consider the field weakening region, require measurement of the inverter's DC bus voltage, resulting in high control costs. Furthermore, they necessitate the introduction of a voltage loop to calculate the current loop output voltage amplitude, compare it with the inverter's maximum output voltage, and provide feedback, making the control methods quite cumbersome.

[0005] Therefore, the present invention requires a permanent magnet synchronous motor control method to simplify the control process and maintain the stability of the dynamic performance of the control. Summary of the Invention

[0006] This invention provides a control method for a permanent magnet synchronous motor that simplifies the control process and maintains the stability of the dynamic performance of the control.

[0007] This invention provides a block diagram of a permanent magnet synchronous motor control system, comprising the following steps:

[0008] S1: Obtain the actual speed of the motor at this moment and compare it with the base speed;

[0009] If the actual rotational speed is less than or equal to the base speed, the MTPA control mode is used.

[0010] If the actual rotational speed is greater than the base speed, the field weakening control mode is adopted and step S2 is executed;

[0011] S2: Obtain the current vector at this moment, and determine the magnitude of the absolute value of the combined voltage of the voltage vector corresponding to the current vector and the absolute value of the maximum phase voltage;

[0012] If the absolute value of the combined voltage is less than the absolute value of the maximum phase voltage, then proceed to step S3;

[0013] If the absolute value of the combined voltage is greater than or equal to the absolute value of the maximum phase voltage, then proceed to step S4;

[0014] S3: Adjust the magnetic weakening current so that it approaches the zero axis for demagnetization; obtain the d-axis current based on the adjusted magnetic weakening current, and output the d-axis current as a d-axis current command to the current controller;

[0015] S4: Adjust the magnetic weakening current so that it is far away from the zero axis to increase magnetization. Obtain the d-axis current based on the adjusted magnetic weakening current and output the d-axis current as a d-axis current command to the current controller.

[0016] Optionally, the d-axis current command output in step S3 is calculated through the following steps:

[0017] ;

[0018] in:

[0019] i dref * This is a d-axis current command;

[0020] i dref_pre The d-axis current before the adjustment of the weakening magnetic current at the previous moment;

[0021] k is a positive constant;

[0022] ω m * This is a reference value for rotational speed;

[0023] ω m This refers to the actual rotational speed.

[0024] Optionally, the d-axis current command output in step S4 is calculated through the following steps:

[0025] ;

[0026] in:

[0027] idref * This is a d-axis current command;

[0028] i dref_pre The d-axis current before the adjustment of the weakening magnetic current at the previous moment;

[0029] k is a positive constant;

[0030] ω m * This is a reference value for rotational speed;

[0031] ω m This refers to the actual rotational speed.

[0032] Optionally, in step S3, the magnetic weakening current uses ke -t Demagnetization is achieved using an exponential decay function, where k is a positive constant and t is time.

[0033] Optionally, in step S4, the magnetic weakening current uses ke t The magnetization is achieved by an exponential growth function, where k is a positive constant and t is time.

[0034] Optionally, step S3 further includes;

[0035] Determine the magnitude of the d-axis current command and the d-axis maximum current threshold.

[0036] If the d-axis current command is less than the maximum d-axis current threshold, then the d-axis current command is output to the current controller.

[0037] If the d-axis current command is greater than or equal to the d-axis maximum current threshold, the d-axis current command is assigned the value of the d-axis maximum current threshold and then output to the current controller.

[0038] Optionally, step S4 further includes;

[0039] Determine the d-axis current command and the d-axis minimum current threshold i dmin Size;

[0040] If the d-axis current command is greater than or equal to the d-axis minimum current threshold i dmin Then the d-axis current command will be output;

[0041] If the d-axis current command is less than the d-axis minimum current threshold i dmin The minimum current threshold i dmin After the value is assigned to the d-axis current command, the d-axis current command is output to the current controller.

[0042] Optionally, step S5 may also be included;

[0043] S5: Determine the combined current vector i of the d-axis current and q-axis current at this moment.s With the maximum line current i limit Relationship;

[0044] If the synthesized current vector i s The absolute value is greater than the maximum line current i limit The absolute value of then generates the q-axis current command i. qref * , to transfer the q-axis current command i qref * Output to current controller;

[0045]

[0046] in:

[0047] i qref * This is a q-axis current command;

[0048] i dref * Let be the d-axis current at that moment;

[0049] i qref_pre This represents the q-axis current at the previous moment.

[0050] Optionally, if the synthesized current vector i s The absolute value is less than or equal to the maximum line current i limit The absolute value of i is then the q-axis current i at that moment. qref_ The value is assigned to the q-axis current command i qref * , to transfer the q-axis current command i qref * Output to the current controller.

[0051] Optionally, if the actual speed is less than or equal to the base speed and the MTPA control mode is used, step S6 is executed;

[0052] S6: Calculate the d-axis current based on the current vector at this moment (command i) dmtpa and the d-axis current command i dmtpa Output to current controller;

[0053] ;

[0054] in:

[0055] ψ f For permanent magnet flux linkage in electric motors;

[0056] L q Let q be the q-axis inductance of the motor;

[0057] L d Let be the d-axis inductance of the motor;

[0058] i q This is the q-axis current at this moment.

[0059] The above control method demonstrates that the speed feedback keeps pace with the reference speed and operates smoothly without speed misalignment, verifying the stable dynamic performance of MTPA and field weakening control. Furthermore, compared to traditional field weakening control methods, the parameter adjustment in this invention is simpler, involving only current parameter adjustment and eliminating the need for a voltage loop. Therefore, it eliminates the need to measure the inverter's DC bus voltage; the corresponding control method can be automatically switched using only the base speed and the actual feedback speed, helping to reduce control costs and complexity. Attached Figure Description

[0060] Figure 1 This is a block diagram of a permanent magnet synchronous motor control system according to an embodiment of the present invention;

[0061] Figure 2 This is an internal block diagram of a current controller according to an embodiment of the present invention;

[0062] Figure 3 This is a flowchart of a permanent magnet synchronous motor control method according to an embodiment of the present invention;

[0063] Figure 4 This is a current vector diagram according to an embodiment of the present invention. Detailed Implementation

[0064] The permanent magnet synchronous motor control method proposed in this invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The advantages and features of this invention will become clearer from the following description. It should be noted that the accompanying drawings are all in a very simplified form and use non-precise scales, and are only used to facilitate and clarify the illustration of the embodiments of this invention.

[0065] In this invention, "outer diameter" and "inner diameter" refer to the diameter of a circular structure, while for a non-circular structure, the inner diameter refers to the diameter of its inscribed circle and the outer diameter refers to the diameter of its circumscribed circle. "Axial direction" refers to the direction of the central axis of a cylindrical rod, while for a non-cylindrical rod, the axial direction refers to the length direction of the rod.

[0066] As used in this invention, the singular forms “a,” “an,” and “the” include plural objects; the term “or” is generally used to mean “and / or”; the term “a number” is generally used to mean “at least one”; and the term “at least two” is generally used to mean “two or more”. Furthermore, the terms “first,” “second,” and “third” are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with “first,” “second,” or “third” may explicitly or implicitly include one or at least two of that feature. Additionally, as used in this invention, “installed,” “connected,” “joined,” and “set” on one element by another should be interpreted broadly, generally indicating only a connection, coupling, mating, or transmission relationship between the two elements, which can be direct or indirect through an intermediate element. They should not be construed as indicating or implying a spatial positional relationship between the two elements, i.e., one element can be located inside, outside, above, below, or to one side of another element, unless otherwise explicitly stated. For those skilled in the art, the specific meaning of the above terms in this invention can be understood according to the specific circumstances. Furthermore, directional terms such as above, below, up, down, upward, downward, left, right, etc., are used relative to exemplary embodiments as shown in the figures, with upward or up direction pointing towards the top of the corresponding figure, and downward or down direction pointing towards the bottom of the corresponding figure.

[0067] This embodiment provides a control method for a permanent magnet synchronous motor, combined with... Figure 1 As shown in the diagram, the control block diagram has an outer speed loop and an inner current loop. The speed loop uses sensors to feed back relevant motor parameters to the speed controller, forming a closed-loop control system. The input to the speed loop is a given speed reference value ω. m * With actual rotational speed ω m The difference between the two values ​​is output as the q-axis current of the current loop.

[0068] The current controller, based on coordinate transformation, converts the three-phase AC current output by the motor into AC and DC axis currents, thus decoupling field control and torque control. The AC control voltage u is generated through the current controller and inverse Park transformation. α and u β The three-phase current i is output through space vector pulse width modulation (SVPWM) and a three-phase inverter. a i b and i c This is used for drive control of permanent magnet synchronous motors (IPMSMs). It converts three-phase AC power into q-axis current i using the Park transform. q and d-axis current id The input is sent to the current controller.

[0069] Combination Figure 2 As shown, the current controller includes d-axis and q-axis current command generators and a decoupled d-axis and q-axis current controller. The d-axis and q-axis current command generators are input to the output value of the speed controller and the speed reference value ω. m * and the actual speed ω of the motor at the current moment. m Motor d-axis voltage u d and motor q-axis voltage u q The d-axis and q-axis current command generator outputs the d-axis current command i. dref * and q-axis current command i qref * The decoupled d-axis and q-axis current controller inputs the d-axis current command i. dref * and q-axis current command i qref * Motor d-axis current i d Motor q-axis current i q Actual rotational speed ω m And the rotation angle θ, and output the motor d-axis voltage u. d and motor q-axis voltage u q .

[0070] Combination Figure 3 As shown, the control method for a permanent magnet synchronous motor includes the following steps:

[0071] S1: Obtain the actual motor speed ω at this moment. m and the base velocity ω b Compare;

[0072] If the actual rotational speed ω m Less than or equal to the base velocity ω b The MTPA control mode is adopted, and step S1-1 is executed;

[0073] If the actual rotational speed ω m Greater than the base velocity ω b The weak magnetic control mode is adopted and step S2 is executed.

[0074] S1-1: Calculate the d-axis current command i based on the current vector at this moment. dmtpa and the d-axis current command i dmtpa Output to current controller;

[0075] ;

[0076] in:

[0077] ψ f For permanent magnet flux linkage in electric motors;

[0078] L q The q-axis inductance of the motor;

[0079] L d The inductance of the motor's d-axis;

[0080] i q This is the q-axis current of the motor at this moment.

[0081] S2: Obtain the current vector at this moment, and determine the magnitude of the absolute value of the combined voltage of the voltage vector corresponding to the current vector and the absolute value of the maximum phase voltage;

[0082] If the absolute value of the combined voltage is less than the absolute value of the maximum phase voltage, then proceed to step S3;

[0083] If the absolute value of the combined voltage is greater than or equal to the absolute value of the maximum phase voltage, then proceed to step S4;

[0084] S3: Adjust the magnetic weakening current so that it approaches the zero axis for demagnetization; obtain the d-axis current based on the adjusted magnetic weakening current, and output the d-axis current as a d-axis current command to the current controller;

[0085] S4: Adjust the magnetic weakening current so that it is far away from the zero axis to increase magnetization. Obtain the d-axis current based on the adjusted magnetic weakening current and output the d-axis current as a d-axis current command to the current controller.

[0086] In step S1, it can be done through Figure 1 The sensor in the middle collects the actual rotational speed ω of the permanent magnet synchronous motor (IPMSM). m And through the speed controller and the base speed ω b Compare them.

[0087] When determining the control strategy, firstly, a mathematical model of the permanent magnet synchronous motor is constructed, including the motor steady-state voltage equation (without neglecting the stator resistance) and the motor torque equation.

[0088] Considering the driver's operating constraints, including voltage and current constraints, calculate the relationship between the motor and the maximum torque-current control ratio in the constant torque region. Define the drive operating point as the intersection of the torque demand curve and the maximum torque-current ratio curve, or the inherent voltage constraint curves of the motor and inverter under different control modes, to facilitate control strategy analysis.

[0089] To decouple the motor model and convert AC quantities to DC quantities, allowing for simpler control of the AC motor similar to that of a DC motor, the voltage equations of the permanent magnet synchronous motor in the three-phase stationary coordinate system are transformed to obtain the steady-state voltage equations in the synchronous rotating coordinate system:

[0090] .

[0091] The motor torque equation is:

[0092]

[0093] in:

[0094] u d This refers to the voltage across the d-axis of the motor.

[0095] u q This is the q-axis voltage of the motor;

[0096] i d This refers to the d-axis current of the motor.

[0097] i q This refers to the q-axis current of the motor.

[0098] p is the number of pole pairs of the motor;

[0099] R s Stator resistance;

[0100] ω e It is the electric angular frequency;

[0101] L q It is the q-axis inductance;

[0102] L d It is the d-axis inductance;

[0103] ψ f It is a permanent magnet flux linkage.

[0104] Considering that the phase voltage of the permanent magnet synchronous motor is limited by the inverter's DC bus voltage, and the line current is limited by the inverter's maximum output current, the voltage and current should satisfy the following during steady-state operation of the motor:

[0105]

[0106] in:

[0107] i limit This represents the maximum line current.

[0108] u limit This represents the magnitude of the maximum phase voltage.

[0109] The stator current vector value of the motor is:

[0110]

[0111] Introduce an auxiliary function F;

[0112]

[0113] MTPA maximum torque / d-axis current formula:

[0114] ;

[0115] And use this d-axis current as the d-axis current command i dmtpa The trajectory is as follows Figure 1 As shown, the maximum current threshold of the d-axis can also be determined through this trajectory (the use of the maximum current threshold of the d-axis is detailed below).

[0116] When the motor is running at high speed, ignoring the effect of stator resistance, the motor's base speed ω b for;

[0117] .

[0118] Base velocity ω b Once determined, it can be compared with the actual rotational speed ω collected by the sensor. m Comparisons are performed to determine the control strategy.

[0119] In this embodiment, in step S2, the magnetic weakening current is adjusted by determining the magnitude of the absolute value of the synthesized voltage and the absolute value of the maximum phase voltage.

[0120] Please continue to refer to this. Figure 4 As shown, if the field weakening control mode is entered, the current vector is further analyzed. Since the motor's operating range is limited by both the motor voltage limit circle and the current limit circle, the motor current vector should be located in the overlapping area of ​​the voltage and current limit circles. Considering the voltage limit again: if the voltage demand corresponding to the current vector at the current moment is within the voltage limit circle, and there is a voltage margin, then step S3 is executed to enter the demagnetizing state. The field weakening current should be slowly reduced to 0 to avoid a sudden increase in torque, which could cause speed fluctuations. If the voltage demand corresponding to the current vector at the current moment is outside the voltage limit circle, and the voltage reaches its limit, then step S4 is executed to enter the magnetizing state. The field weakening current should increase rapidly to prevent the current controller from malfunctioning.

[0121] For further details, please refer to... Figure 3 As shown,

[0122] When not satisfied Under certain conditions, the absolute value of the combined voltage is considered to be less than the absolute value of the maximum phase voltage, and then the process proceeds... Figure 3 In process A, demagnetization is performed in step S3.

[0123] In preferred step S3, the magnetic weakening current uses ke -t Demagnetization is achieved using an exponential decay function (weakening current approaches the 0 axis), where k is a positive constant and t is time. At this time, the d-axis current increases, and the d-axis current command is calculated through the following steps:

[0124] ;

[0125] in:

[0126] i dref * This is a d-axis current command;

[0127] i dref_pre This represents the d-axis current before the adjustment of the magnetic weakening current at the previous moment. In this embodiment, the sampling period is 50μs, so the previous moment represents the d-axis current collected in the previous period.

[0128] k is a positive constant;

[0129] ω m * This is a reference value for rotational speed;

[0130] ω m This refers to the actual rotational speed.

[0131] As can be seen from the above d-axis current command formula, when the absolute value of the synthesized voltage is less than the absolute value of the maximum phase voltage (the voltage vector is located within the voltage limit circle), it indicates that the system has a voltage margin, and at this time, it should enter the demagnetizing state. To ensure the smoothness of the exit process and avoid sudden torque increases and speed oscillations caused by a sudden decrease in the demagnetizing current, the demagnetizing process uses a ke... -t Implemented using an exponential decay function.

[0132] For further details, please refer to... Figure 3 As shown, step S3 ( Figure 3 Process A) also includes;

[0133] When the d-axis current command i is calculated using the above formula in step S3... dref * Then, determine the d-axis current command i. dref * The magnitude of the d-axis maximum current threshold, where the d-axis maximum current threshold is determined by the formula i = MTPA maximum torque / d-axis current. dmtpa Sure.

[0134] If the d-axis current command is less than the d-axis maximum current threshold, then output the d-axis current command i. dref * To the current controller;

[0135] If the d-axis current command is greater than or equal to the d-axis maximum current threshold, assign the value of the d-axis maximum current threshold to the d-axis current command i. dref * At this time, the d-axis current command i dref * The current threshold is equal to the maximum current threshold of the d-axis, and then the d-axis current command i is output. dref * To the current controller.

[0136] In step S3, when entering Figure 3 During process A, the inverter output voltage did not reach its upper limit, and the system slowly entered the demagnetizing state. The d-axis current command i was calculated using the designed demagnetizing algorithm. dref * The maximum current threshold along the d-axis is calculated using the MTPA formula, and the two are compared. If i dref * ＞ i dmtpa (Maximum current threshold on the d-axis), select i dmtpa (Maximum current threshold of d-axis) serves as the d-axis reference command i dref * This allows the system to return to its optimal operating point; if i dref * ＜ i dmtpa Directly select the i calculated above. dref * As a d-axis reference command, it keeps the system at a certain level of magnetic weakness and gradually exits the magnetic weakness state.

[0137] Please continue to refer to this. Figure 3 As shown, when the following conditions are met If the conditions are met, the absolute value of the synthesized voltage is considered to be greater than or equal to the absolute value of the maximum phase voltage, and then the process enters step B to execute step S4 for magnetization.

[0138] In preferred step S4, the magnetic weakening current uses ke t An exponential growth function is used to increase magnetization (weakening current moves away from the 0 axis), where k is a positive constant and t is time. At this time, the d-axis current decreases, and the d-axis current command is calculated through the following steps:

[0139] .

[0140] As can be seen from the above d-axis current command formula, when the absolute value of the synthesized voltage is greater than or equal to the absolute value of the maximum phase voltage (the synthesized voltage vector is located outside the voltage limit circle), it indicates that the system voltage resources have reached their limit, and there is a risk of current runaway. At this time, it is necessary to quickly enhance the magnetic weakening effect, using Ke... t The exponential growth function enables a rapid response.

[0141] Furthermore, step S4 ( Figure 3 Process B) also includes;

[0142] Determine the d-axis current command i calculated by the above formula. dref * minimum current threshold i along the d-axis dmin The size of , where the minimum current threshold i dmin Depend on Figure 4 The intersection point of the intermediate current loop and the negative half-axis of the d-axis is determined.

[0143] If the d-axis current command i dref * Greater than or equal to the minimum current threshold i along the d-axis dmin Then, the d-axis current command i calculated by the above formula will be directly output. dref * ;

[0144] If the d-axis current command i dref * Less than the minimum current threshold i along the d-axis dmin The minimum current threshold i dmin The value is assigned to the d-axis current command i dref * At this time i dref * =i dmin Then output the updated d-axis current command i dref * To the current controller.

[0145] In step 4, when entering Figure 3 During process B, the inverter output voltage reaches its upper limit, and the system quickly enters a field weakening state. The d-axis current reference value i is calculated using the designed field weakening algorithm. dref * However, to ensure the safe operation of the system, the minimum d-axis current i is used. dmin Limiting is applied to prevent the total stator current from exceeding the inverter's current output capacity.

[0146] Furthermore, after calculating the d-axis current command i dref * Then, it also includes step S5;

[0147] S5: Determine the d-axis current i at this moment. d and q-axis current i q Composite current vector i s With the maximum line current i limit The relationship.

[0148] like Figure 3 As shown, ,like If the condition is satisfied, then the resultant current vector i is considered to be... s The absolute value is greater than the maximum line current i limit The absolute value of the resultant current vector i is then obtained. s If the current limit is exceeded, a q-axis current command i is generated. qref * , to transfer the q-axis current command i qref * Output to current controller;

[0149]

[0150] in:

[0151] i qref * This is a q-axis current command;

[0152] i dref * This is the d-axis current at that moment, which is equal to the d-axis current command.

[0153] i qref_pre The current at the previous moment is the q-axis current. In this embodiment, the sampling period is 50μs, so the current at the previous moment is the q-axis current collected in the previous period.

[0154] like If the condition is not met, then the resultant current vector i is considered to be... s The absolute value is less than or equal to the maximum line current i limit The absolute value of the resultant current vector i is then obtained. s If the current limit cycle has not been exceeded, then the q-axis current i at that moment is... qref_ The value is assigned to the q-axis current command i qref * , to transfer the q-axis current command i qref * The output is sent to the current controller. Through the current vector i... s The absolute value of the maximum line current i limit The absolute value of the comparison determines whether the synthesized current vector exceeds the current limit circle, and the corresponding q-axis current command i is output. qref * .

[0155] The above control method demonstrates that the speed feedback keeps pace with the reference speed and operates smoothly without speed misalignment, verifying the stable dynamic performance of MTPA and field weakening control. Furthermore, compared to traditional field weakening control methods, the parameter adjustment in this invention is simpler, involving only current parameter adjustment and eliminating the need for a voltage loop. Therefore, it eliminates the need to measure the inverter's DC bus voltage; the corresponding control method can be automatically switched using only the base speed and the actual feedback speed, helping to reduce control costs and complexity.

[0156] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0157] The above description is merely a description of preferred embodiments of the present invention and is not intended to limit the scope of the present invention in any way. Any changes or modifications made by those skilled in the art based on the above disclosure shall fall within the protection scope of the claims.

Claims

1. A control method for a permanent magnet synchronous motor, characterized in that, Includes the following steps: S1: Obtain the actual speed of the motor at this moment and compare it with the base speed; If the actual rotational speed is less than or equal to the base speed, the MTPA control mode is used. If the actual rotational speed is greater than the base speed, the field weakening control mode is adopted and step S2 is executed; S2: Obtain the current vector at this moment, and determine the magnitude of the absolute value of the combined voltage of the voltage vector corresponding to the current vector and the absolute value of the maximum phase voltage; If the absolute value of the combined voltage is less than the absolute value of the maximum phase voltage, then proceed to step S3; If the absolute value of the combined voltage is greater than or equal to the absolute value of the maximum phase voltage, then proceed to step S4; S3: Adjust the magnetic weakening current so that it approaches the zero axis for demagnetization; obtain the d-axis current based on the adjusted magnetic weakening current, and output the d-axis current as a d-axis current command to the current controller; S4: Adjust the magnetic weakening current so that it is far from the zero axis to increase magnetization; The d-axis current is obtained based on the adjusted magnetic weakening current, and the d-axis current is output as a d-axis current command to the current controller.

2. The permanent magnet synchronous motor control method as described in claim 1, characterized in that, The d-axis current command output in step S3 is calculated through the following steps: ； in: i dref * This is a d-axis current command; i dref_pre The d-axis current before the adjustment of the weakening magnetic current at the previous moment; k is a positive constant; ω m * This is a reference value for rotational speed; ω m This is the actual rotational speed.

3. The permanent magnet synchronous motor control method as described in claim 1, characterized in that, The d-axis current command output in step S4 is calculated through the following steps: ； in: i dref * This is a d-axis current command; i dref_pre The d-axis current before the adjustment of the weakening magnetic current at the previous moment; k is a positive constant; ω m * This is a reference value for rotational speed; ω m This is the actual rotational speed.

4. The permanent magnet synchronous motor control method as described in claim 1, characterized in that, In step S3, the magnetic weakening current uses ke -t Demagnetization is achieved using an exponential decay function, where k is a positive constant and t is time.

5. The permanent magnet synchronous motor control method as described in claim 1, characterized in that, In step S4, the magnetic weakening current uses ke t The magnetization is achieved by an exponential growth function, where k is a positive constant and t is time.

6. The permanent magnet synchronous motor control method as described in claim 1, characterized in that, Step S3 also includes: Determine the magnitude of the d-axis current command and the d-axis maximum current threshold. If the d-axis current command is less than the maximum d-axis current threshold, then the d-axis current command is output to the current controller. If the d-axis current command is greater than or equal to the d-axis maximum current threshold, the d-axis current command is assigned the value of the d-axis maximum current threshold and then output to the current controller.

7. The permanent magnet synchronous motor control method as described in claim 1, characterized in that, Step S4 also includes: Determine the magnitude of the d-axis current command and the d-axis minimum current threshold. If the d-axis current command is greater than or equal to the minimum d-axis current threshold, then the d-axis current command is output to the current controller. If the d-axis current command is less than the minimum d-axis current threshold, the minimum current threshold value is assigned to the d-axis current command, and then the d-axis current command is output to the current controller.

8. The permanent magnet synchronous motor control method as described in claim 1, characterized in that, It also includes step S5; S5: Determine the combined current vector i of the d-axis current and q-axis current at this moment. s With the maximum line current i limit Relationship; If the synthesized current vector i s The absolute value is greater than the maximum line current i limit The absolute value of generates the q-axis current command i. qref * The q-axis current command i qref * Output to current controller; in: i qref * This is a q-axis current command; i dref * Let be the d-axis current at that moment; i qref_pre This represents the q-axis current at the previous moment.

9. The permanent magnet synchronous motor control method as described in claim 8, characterized in that, If the synthesized current vector i s The absolute value is less than or equal to the maximum line current i limit The absolute value of i is then the q-axis current i at that moment. qref_ The value is assigned to the q-axis current command i qref * Then, the q-axis current command i is output. qref * To the current controller.

10. The permanent magnet synchronous motor control method as described in claim 1, characterized in that, If the actual speed is less than or equal to the base speed, and the MTPA control mode is used, proceed to step S6. S6: Calculate the d-axis current based on the current vector at this moment (command i) dmtpa and the d-axis current command i dmtpa Output to current controller; ； in: ψ f For permanent magnet flux linkage in electric motors; L q Let q be the q-axis inductance of the motor; L d Let be the d-axis inductance of the motor; i q This is the q-axis current at this moment.

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