A method and system for controlling variable magnetic flux of a permanent magnet synchronous motor

Abstract

The present invention relates to a control method and system for variable magnetic flux of a permanent magnet synchronous motor, and the control method includes: obtaining the motor speed and current value of the permanent magnet synchronous motor; obtaining the magnetization direction of each magnetic steel according to the current value and the motor speed; confirming whether to charge and demagnetize the magnetic steel according to the motor speed of the permanent magnet synchronous motor and the magnetization direction of each magnetic steel; when charging and demagnetizing the magnetic steel, generating a direct-axis pulse current according to the motor speed and the current value to charge and demagnetize the magnetic steel. The embodiment of the present invention obtains the motor speed and current value of the permanent magnet synchronous motor, and confirms the magnetization direction of each magnetic steel of the permanent magnet synchronous motor according to the motor speed and the current value, confirms whether charging and demagnetization is required according to the motor speed and the magnetization direction, and generates a direct-axis pulse current to charge and demagnetize the magnetic steel when charging and demagnetization is required, and changes the strength of the magnetic field inside the motor in real time, so as to expand the speed range of the motor without passing a weak magnetic current.

Description

Technical Field

[0001] The present invention relates to the technical field of permanent magnet synchronous motors, and in particular to a method and system for controlling variable magnetic flux of a permanent magnet synchronous motor. Background Art

[0002] In recent years, the drive motors for new energy vehicles mostly use internal permanent magnet synchronous motors (IPMSM), which have the advantages of high power density, good mechanical properties, and a high speed range. They have received extensive attention and application in electric vehicle drive systems. However, the direct-axis inductance of the internal permanent magnet synchronous motor is usually smaller than the quadrature-axis inductance. In order to utilize the reluctance torque and realize weak magnetic control, the current trajectory is located in the second quadrant, and the current always contains a weak magnetic component, which increases the loss and the utilization rate of the magnetic steel is low. In addition, after the motor enters the high-speed stage, it is necessary to weaken the motor by increasing the direct-axis demagnetization current component to control the motor terminal voltage not to exceed the limit value of the inverter voltage. At this time, the larger weak magnetic current increases the copper loss of the motor, resulting in a decrease in the efficiency of the motor. In addition, due to the limitation of the inverter power level, the current also has a limit value, which limits the weak magnetic degree of the motor and narrows the adjustable speed range.

[0003] The prior art proposes a mechanical magnetic modulation type permanent magnet synchronous motor, which uses a mechanical magnetic modulation device to change the strength of the magnetic field inside the motor, thereby reducing the weak magnetic current at high speed and improving the working efficiency of the motor. However, the magnetic modulation device of the mechanical magnetic modulation type permanent magnet motor is relatively complex and increases the volume and weight of the entire motor to a certain extent, so it is not conducive to improving the power density and efficiency of the motor. Summary of the invention

[0004] In order to solve the problems existing in the prior art, at least one embodiment of the present invention provides a method and system for controlling variable magnetic flux of a permanent magnet synchronous motor.

[0005] In a first aspect, an embodiment of the present invention provides a method for controlling variable magnetic flux of a permanent magnet synchronous motor, wherein the rotor permanent magnet of the permanent magnet synchronous motor includes a plurality of magnetic steels, wherein the magnetic steels include at least one magnetizing and demagnetizing magnetic steel made of a low coercive force permanent magnet material, and the control method includes:

[0006] Obtaining the motor speed and current value of the permanent magnet synchronous motor;

[0007] Obtaining the magnetization direction of each magnetic steel according to the current value and the motor speed;

[0008] Determining whether to charge and demagnetize the charging and demagnetizing magnetic steel according to the motor speed of the permanent magnet synchronous motor and the magnetization direction of each magnetic steel;

[0009] When the demagnetizing magnetic steel is charged and demagnetized, a direct-axis pulse current is generated according to the motor speed and the current value to charge and demagnetize the demagnetizing magnetic steel.

[0010] Based on the above technical solution, the embodiment of the present invention can also make the following improvements.

[0011] In combination with the first aspect, in a first embodiment of the first aspect, determining whether to charge and demagnetize the charging and demagnetizing magnetic steel according to the motor speed of the permanent magnet synchronous motor and the magnetization direction of each of the magnetic steels specifically includes:

[0012] Comparing the motor speed with a preset threshold range to determine the operating state of the permanent magnet synchronous motor;

[0013] Comparing the magnetization directions of all the magnetic steels to determine whether the magnetization directions of all the magnetic steels are consistent;

[0014] When the motor speed is less than the minimum value of the preset threshold range and the magnetization directions of all the magnetic steels are consistent, magnetizing the charging and demagnetizing magnetic steels;

[0015] Alternatively, when the motor speed meets the preset threshold range, the magnet steel is not charged or demagnetized;

[0016] Alternatively, when the motor speed is greater than the maximum value of the preset threshold range and the magnetization direction of the demagnetization magnetic steel is inconsistent with that of the other magnetic steels, the demagnetization magnetic steel is demagnetized.

[0017] In combination with the first embodiment of the first aspect, in the second embodiment of the first aspect, when the permanent magnet synchronous motor is charged and demagnetized, a direct-axis pulse current is generated according to the motor speed and the current value to charge and demagnetize the charging and demagnetization magnetic steel, specifically including:

[0018] When the demagnetized magnetic steel is magnetized;

[0019] The forward direct-axis pulse current value is calculated by the following formula using the iteration method:

[0020] n(k+1)=p×n(k)+q1×i(k);

[0021] i(k)=i inv (k)+i d (k);

[0022] Wherein, n(k+1) is the motor speed at time k+1, p is the torque pulsation, n(k) is the motor speed at time k, q1 is the magnetization constant coefficient corresponding to the preset speed, i(k) is the winding current value at time k, i inv(k) is the supply current value at time k, i d (k) is the direct-axis pulse current at time k;

[0023] Generating a direct-axis pulse current according to the positive direct-axis pulse current value and converting it into alternating current;

[0024] The alternating current and the power supply current of the permanent magnet synchronous motor are synthesized and output to the permanent magnet synchronous motor.

[0025] In combination with the first embodiment of the first aspect, in a third embodiment of the first aspect, when the permanent magnet synchronous motor is charged and demagnetized, a direct-axis pulse current is generated according to the motor speed and the winding current value to charge and demagnetize the charging and demagnetization magnetic steel, specifically including:

[0026] When the demagnetized magnetic steel is demagnetized;

[0027] The reverse direct-axis pulse current value is calculated by the following formula using the iteration method:

[0028] n(k+1)=p×n(k)-q2×i(k);

[0029] i(k)=i inv (k)-i d (k);

[0030] Wherein, n(k+1) is the motor speed at time k+1, p is the torque pulsation, n(k) is the motor speed at time k, q2 is the magnetization constant coefficient corresponding to the preset speed, i(k) is the winding current value at time k, i inv (k) is the supply current value at time k, i d (k) is the direct-axis pulse current at time k;

[0031] Generate a direct-axis pulse current according to the reverse direct-axis pulse current value and convert it into alternating current;

[0032] The alternating current and the power supply current of the permanent magnet synchronous motor are synthesized and output to the permanent magnet synchronous motor.

[0033] In combination with the first aspect or the first, second or third embodiment of the first aspect, in a fourth embodiment of the first aspect, obtaining the motor speed and current value of the permanent magnet synchronous motor specifically includes:

[0034] Obtaining a rotor position of the permanent magnet synchronous motor;

[0035] Performing differentiation processing on the rotor position to obtain the motor speed of the permanent magnet synchronous motor;

[0036] Obtaining a winding current value of the permanent magnet synchronous motor;

[0037] A supply current value and a direct-axis pulse current are obtained according to the winding current value.

[0038] In a second aspect, an embodiment of the present invention further provides a control system for a variable magnetic flux of a permanent magnet synchronous motor, wherein the rotor permanent magnet of the permanent magnet synchronous motor includes a plurality of magnetic steels, and the magnetic steels include at least one magnetizing and demagnetizing magnetic steel made of a low coercive force permanent magnet material; the control system includes:

[0039] A current conditioning circuit connected to the permanent magnet synchronous motor for obtaining a current value of the permanent magnet synchronous motor;

[0040] A speed analyzer disposed at a corresponding position of the permanent magnet synchronous motor for detecting the motor speed of the permanent magnet synchronous motor;

[0041] A flux observer connected to the current conditioning circuit and the speed analyzer respectively, wherein the flux observer confirms the magnetization direction of each magnetic steel according to the current value and the motor speed;

[0042] A processor connected to the flux observer and the speed analyzer respectively, the processor confirming whether to charge and demagnetize the charging and demagnetizing magnetic steel according to the motor speed and the magnetization direction of each magnetic steel;

[0043] A charging and demagnetizing converter connected to the power supply circuit of the permanent magnet synchronous motor and the processor respectively.

[0044] In combination with the second aspect, in a first embodiment of the second aspect, the processor includes: a determiner and a calculator;

[0045] The judger is respectively connected to the flow conditioning circuit, the speed analyzer, and the calculator;

[0046] The calculator is connected to the charging and demagnetizing converter.

[0047] In combination with the first embodiment of the second aspect, in a second embodiment of the second aspect, the rotation speed analyzer includes: a position sensor and a speed analyzer;

[0048] The position sensor is connected to the speed analyzer;

[0049] The speed analyzer is connected to the flux observer and the processor respectively.

[0050] In combination with the second aspect or the first or second embodiment of the second aspect, in a third embodiment of the second aspect, the charging and demagnetizing converter includes: a pulse current exciter and a function generator;

[0051] The processor, the pulse current exciter, the function generator, and the power supply circuit of the permanent magnet synchronous motor are connected in sequence.

[0052] In combination with the third embodiment of the second aspect, in a fourth embodiment of the second aspect, the control system further includes: an inverter, a speed regulator, and a drive circuit;

[0053] The speed analyzer, the speed regulator, the drive circuit, the inverter, the power supply circuit of the permanent magnet synchronous motor, and the permanent magnet synchronous motor are connected in sequence.

[0054] The above technical scheme of the present invention has the following advantages compared with the prior art: the embodiment of the present invention obtains the motor speed and current value of the permanent magnet synchronous motor, and confirms the magnetization direction of each magnetic steel of the permanent magnet synchronous motor according to the motor speed and current value, and confirms whether charging and demagnetization are required according to the motor speed and magnetization direction. When charging and demagnetization are required, a direct-axis pulse current is generated to realize charging and demagnetization of the magnetic steel, and the strength of the magnetic field inside the motor is changed in real time, so that the speed range of the motor can be expanded without passing a weak magnetic current. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 It is a flow chart of a method for controlling variable magnetic flux of a permanent magnet synchronous motor provided by an embodiment of the present invention;

[0056] Figure 2 It is a flow chart of a method for controlling variable magnetic flux of a permanent magnet synchronous motor provided by another embodiment of the present invention;

[0057] Figure 3 This is a flow chart of a method for controlling variable magnetic flux of a permanent magnet synchronous motor provided by another embodiment of the present invention;

[0058] Figure 4 This is a second flow chart of a method for controlling variable magnetic flux of a permanent magnet synchronous motor provided by another embodiment of the present invention;

[0059] Figure 5 It is a schematic structural diagram of a control system for variable magnetic flux of a permanent magnet synchronous motor provided by another embodiment of the present invention. DETAILED DESCRIPTION

[0060] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0061] like Figure 1 As shown, an embodiment of the present invention provides a method for controlling variable magnetic flux of a permanent magnet synchronous motor.

[0062] The rotor permanent magnet of the permanent magnet synchronous motor includes a plurality of magnetic steels, and the magnetic steels include at least one magnetizing and demagnetizing magnetic steel made of low coercive force permanent magnetic material. A permanent magnet synchronous motor is a synchronous motor that generates a synchronous rotating magnetic field by excitation of a permanent magnet. The permanent magnet acts as a rotor to generate a rotating magnetic field. The three-phase stator winding induces a three-phase symmetrical current through an armature reaction under the action of the rotating magnetic field. The rotor of the permanent magnet synchronous motor can be any number of magnets. The magnet is used to generate a magnetic field. Since the magnetization direction of magnets made of permanent magnetic materials with different coercive forces has different stability and will also change due to the thickness of the magnet, in this embodiment, the rotor of the permanent magnet synchronous motor is composed of at least one magnet made of low coercive force. Coercive force refers to the magnetic material after saturation magnetization. When the external magnetic field returns to zero, its magnetic induction intensity does not return to zero. Only when a magnetic field of a certain size is added in the opposite direction of the original magnetization field can the magnetic induction intensity return to zero. This magnetic field is called a coercive magnetic field, also known as coercive force. For example, an aluminum nickel cobalt permanent magnet. Compared with an aluminum nickel cobalt permanent magnet, a permanent magnet with a higher coercive force is a neodymium iron boron permanent magnet. The ferromagnetic current of a permanent magnet with a higher coercive force is higher, and demagnetization will not occur under normal conditions.

[0063] The control method of variable flux of permanent magnet synchronous motor includes:

[0064] S11. Obtain the motor speed and current value of the permanent magnet synchronous motor.

[0065] In this embodiment, the motor speed of the permanent magnet synchronous motor can be obtained through a speed measuring device or a position detection device. The speed can be obtained by the speed detection device after calculation, and the current value of the permanent magnet synchronous motor can be obtained through a current detection device, wherein the current value includes: the three-phase alternating current inverted by the inverter from the DC power supply and the alternating current applied to generate a short-time direct-axis pulse current, which is converted into direct current, which are the power supply current value and the direct-axis pulse current value respectively.

[0066] In this embodiment, the method for obtaining the motor speed includes:

[0067] The rotor position of the permanent magnet synchronous motor is obtained, and the motor speed of the permanent magnet synchronous motor is obtained by performing differential processing on the rotor position.

[0068] The method for obtaining the current value of the permanent magnet synchronous motor includes:

[0069] The winding current value of the permanent magnet synchronous motor is obtained, and the power supply current value and the direct-axis pulse current are obtained according to the winding current value.

[0070] S12. Obtain the magnetization direction of each magnetic steel according to the current value and the motor speed.

[0071] In this embodiment, the magnetization direction of each magnet can be obtained by analyzing the current value and the motor speed through a flux observer, wherein the magnetization direction of the magnet made of a permanent magnetic material with a higher coercive force will not change easily, while the magnet made of a permanent magnetic material with a weaker coercive force will be demagnetized during use, resulting in a change in the magnetization direction, causing the motor to be unable to operate in a larger speed range.

[0072] S13, confirming whether to charge and demagnetize the magnetic steel according to the motor speed of the permanent magnet synchronous motor and the magnetization direction of each magnetic steel.

[0073] In the present embodiment, when the magnetization directions of the various magnets are consistent, the effect of the magnets on the air gap permanent magnetic flux of the motor is enhanced. At this time, if the motor speed is less than the minimum value of the preset range, it is necessary to magnetize the demagnetized magnets so that the motor speed can continue to decrease, thereby increasing the lower limit of the motor speed. When the magnetization directions of the various magnets are inconsistent, the effect of the magnets on the air gap permanent magnetic flux of the motor is weakened. At this time, if the motor speed is greater than the maximum value of the preset range, it is necessary to demagnetize the demagnetized magnets so that the motor speed can continue to increase, thereby providing an upper limit of the motor speed. When the motor speed is within the preset range, it is not necessary to charge and demagnetize the magnets. Therefore, in the present embodiment, whether charging and demagnetization is required is determined based on the magnetization direction of the magnet and the motor speed.

[0074] Specifically, the method for confirming whether the demagnetized magnetic steel is demagnetized includes:

[0075] S21. Compare the motor speed with the preset threshold range to determine the operating state of the permanent magnet synchronous motor; the operating states include: high-speed operation, that is, the motor speed is greater than the upper limit of the preset threshold range; or, low-speed operation, that is, the motor speed is less than the lower limit of the preset threshold range; or, stable operation, that is, the motor speed is within the preset threshold range.

[0076] S22, comparing the magnetization directions of all the magnetic steels to determine whether the magnetization directions of all the magnetic steels are consistent;

[0077] S23a, when the motor speed is less than the minimum value of the preset threshold range and the magnetization directions of all the magnetic steels are consistent, magnetizing the magnetic steels to be charged and demagnetized;

[0078] S23b, or, when the motor speed meets the preset threshold range, the magnet steel is not charged and demagnetized;

[0079] S23c, or, when the motor speed is greater than the maximum value of the preset threshold range, and the magnetization directions of the demagnetized magnetic steel and other magnetic steels are inconsistent, the demagnetized magnetic steel is demagnetized.

[0080] S14. When the magnetic steel is charged and demagnetized, a direct-axis pulse current is generated according to the motor speed and current value to charge and demagnetize the magnetic steel.

[0081] In this embodiment, when it is confirmed that the magnet needs to be charged and demagnetized, a direct-axis pulse current is generated by the motor speed and current value, and the direct-axis pulse current is converted into alternating current and integrated with the power supply AC point to power the stator of the motor, thereby achieving charging and demagnetization of the rotor magnet.

[0082] like Figure 3 As shown, the embodiment of the present invention also provides a method for controlling the variable magnetic flux of a permanent magnet synchronous motor. Figure 1 Compared with the control method shown in the figure, the difference is:

[0083] When the demagnetized magnetic steel is magnetized.

[0084] S31. Calculate the positive direct-axis pulse current value by the following calculation formula using an iterative method:

[0085] n(k+1)=p×n(k)+q1×i(k);

[0086] i(k)=i inv (k)+i d (k);

[0087] Among them, n(k+1) is the motor speed at time k+1, p is the torque pulsation, n(k) is the motor speed at time k, q1 is the magnetization constant coefficient corresponding to the preset speed, i(k) is the winding current value at time k, i inv (k) is the supply current value at time k, i d (k) is the direct-axis pulse current at time k; the corresponding direct-axis pulse current value is obtained by iterating the above formula; during the rotation of the motor, the instantaneous output torque changes with time, but it fluctuates around a certain average value, and this phenomenon is called torque pulsation. The value of the magnetization degree constant coefficient is large at low speed, and gradually decreases as the speed increases, and is inversely correlated with the speed. The relationship between the speed and this value can be determined through experiments or practical applications and stored for subsequent use.

[0088] S32, generating a direct-axis pulse current according to the positive direct-axis pulse current value and converting it into alternating current.

[0089] A corresponding direct-axis pulse current is generated according to the calculated direct-axis pulse current value and converted into alternating current.

[0090] S33, synthesizing the alternating current and the power supply current of the permanent magnet synchronous motor and outputting the resultant to the permanent magnet synchronous motor.

[0091] In this embodiment, the alternating current converted from the direct-axis pulse current is synthesized with the power supply current of the permanent magnet synchronous motor, and the synthesized alternating current is output to the permanent magnet synchronous motor, thereby realizing power supply to the permanent magnet synchronous motor and magnetization of the permanent magnet synchronous motor rotor.

[0092] like Figure 4 As shown, the embodiment of the present invention also provides a method for controlling the variable magnetic flux of a permanent magnet synchronous motor. Figure 1 Compared with the control method shown in the figure, the difference is:

[0093] When demagnetizing the demagnetized magnetic steel.

[0094] S41. Calculate the reverse direct-axis pulse current value by using the following calculation formula using an iterative method:

[0095] n(k+1)=p×n(k)-q2×i(k);

[0096] i(k)=i inv (k)-i d (k);

[0097] Among them, n(k+1) is the motor speed at time k+1, p is the torque ripple, n(k) is the motor speed at time k, q2 is the magnetization constant coefficient corresponding to the preset speed, i(k) is the winding current value at time k, i inv (k) is the supply current value at time k, i d (k) is the direct-axis pulse current at time k; the corresponding direct-axis pulse current value is obtained by iterating the above formula; during the rotation of the motor, the instantaneous output torque changes with time, but it fluctuates around a certain average value, and this phenomenon is called torque pulsation. The value of the magnetization degree constant coefficient is large at low speed, and gradually decreases as the speed increases, and is inversely correlated with the speed. The relationship between the speed and this value can be determined through experiments or practical applications and stored for subsequent use.

[0098] S42, generating a direct-axis pulse current according to the reverse direct-axis pulse current value and converting it into alternating current.

[0099] S43, synthesizing the alternating current and the power supply current of the permanent magnet synchronous motor and outputting the resultant to the permanent magnet synchronous motor.

[0100] In this embodiment, the alternating current converted from the direct-axis pulse current is synthesized with the power supply current of the permanent magnet synchronous motor, and the synthesized alternating current is output to the permanent magnet synchronous motor, thereby powering the permanent magnet synchronous motor and demagnetizing the permanent magnet synchronous motor rotor.

[0101] like Figure 5As shown, an embodiment of the present invention further provides a control system for variable magnetic flux of a permanent magnet synchronous motor, wherein the rotor permanent magnet of the permanent magnet synchronous motor includes a plurality of magnets, and the magnets include at least one magnetized and demagnetized magnet made of a low coercive force permanent magnet material.

[0102] In this embodiment, the control system includes: a current conditioning circuit connected to the permanent magnet synchronous motor for obtaining the current value of the permanent magnet synchronous motor. The current conditioning circuit can analyze the obtained current value of the permanent magnet synchronous motor and transform the three-phase alternating current into a direct current supply current value and a direct-axis pulse current through coordinate transformation.

[0103] In this embodiment, the control system includes: a speed analyzer arranged at a corresponding position of the permanent magnet synchronous motor for detecting the motor speed of the permanent magnet synchronous motor, and the motor speed is analyzed by the speed analyzer.

[0104] In this embodiment, the speed analyzer includes: a position sensor and a speed analyzer; the position sensor is connected to the speed analyzer; the speed analyzer is respectively connected to the flux observer and the processor. Through the speed analyzer, in this embodiment, the rotor position of the permanent magnet synchronous motor is detected by the position sensor, and the motor speed of the permanent magnet synchronous motor can be obtained by differentiating the rotor position.

[0105] In this embodiment, the control system includes: a flux observer connected to the current conditioning circuit and the speed analyzer respectively, the flux observer confirms the magnetization direction of each magnetic steel according to the current value and the motor speed. In this embodiment, the magnetization direction of the magnetic steel is detected by the flux observer.

[0106] In this embodiment, the control system includes: a processor connected to the flux observer and the speed analyzer respectively, the processor confirms whether to charge and demagnetize the magnetic steel according to the motor speed and the magnetization direction of each magnetic steel, and the processor includes: a judger and a calculator; the judger is connected to the current conditioning circuit, the speed analyzer, and the calculator respectively; the calculator is connected to the charging and demagnetization converter, and the processor confirms whether to charge and demagnetize the magnetic steel according to the motor speed of the permanent magnet synchronous motor and the magnetization direction of each magnetic steel.

[0107] In this embodiment, the control system includes: a charging and demagnetizing converter connected to the power supply circuit of the permanent magnet synchronous motor and the processor respectively, and the charging and demagnetizing converter includes: a pulse current exciter and a function generator; the processor, the pulse current exciter, the function generator, and the power supply circuit of the permanent magnet synchronous motor are connected in sequence, the pulse current exciter is used to generate a direct-axis pulse current based on the calculated direct-axis pulse current value, and the function generator is used to generate three-phase alternating current from the direct-axis pulse current to meet the three-phase alternating current power supply of the permanent magnet synchronous motor.

[0108] In this embodiment, the control system also includes: an inverter, a speed regulator and a drive circuit. The speed analyzer, the speed regulator, the drive circuit, the inverter, the power supply circuit of the permanent magnet synchronous motor, and the permanent magnet synchronous motor are connected in sequence. In this embodiment, the inverter is used to convert direct current into three-phase alternating current to power the motor. The speed regulator obtains the difference between the motor speed obtained by the speed analyzer and the expected speed, and inputs the speed difference into the drive circuit. The drive circuit controls the inverter to convert direct current into three-phase alternating current according to the speed difference, thereby controlling the motor speed of the permanent magnet synchronous motor.

[0109] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for controlling variable magnetic flux of a permanent magnet synchronous motor, wherein the rotor permanent magnet of the permanent magnet synchronous motor comprises a plurality of magnetic steels, wherein the magnetic steels comprise at least one magnetizing and demagnetizing magnetic steel made of a low coercive force permanent magnet material; characterized in that: The control method comprises: Obtaining the motor speed and current value of the permanent magnet synchronous motor; Obtaining the magnetization direction of each magnetic steel according to the current value and the motor speed; Determining whether to charge and demagnetize the charging and demagnetizing magnetic steel according to the motor speed of the permanent magnet synchronous motor and the magnetization direction of each magnetic steel; When the demagnetizing magnetic steel is charged and demagnetized, a direct-axis pulse current is generated according to the motor speed and the current value to charge and demagnetize the demagnetizing magnetic steel, specifically including: When the demagnetized magnetic steel is magnetized; The forward direct-axis pulse current value is calculated by the following formula using the iteration method: n(k+1)=p×n(k)+q1×i(k); i(k)=i inv (k)+i d (k); Wherein, n(k+1) is the motor speed at time k+1, p is the torque pulsation, n(k) is the motor speed at time k, q1 is the magnetization constant coefficient corresponding to the preset speed, i(k) is the winding current value at time k, i inv (k) is the supply current value at time k, i d (k) is the direct-axis pulse current at time k; Generating a direct-axis pulse current according to the positive direct-axis pulse current value and converting it into alternating current; The alternating current and the power supply current of the permanent magnet synchronous motor are synthesized and output to the permanent magnet synchronous motor.

2. The control method according to claim 1, characterized in that: The step of determining whether to charge and demagnetize the charging and demagnetizing magnetic steel according to the motor speed of the permanent magnet synchronous motor and the magnetization direction of each magnetic steel specifically includes: Comparing the motor speed with a preset threshold range to determine the operating state of the permanent magnet synchronous motor; Comparing the magnetization directions of all the magnetic steels to determine whether the magnetization directions of all the magnetic steels are consistent; When the motor speed is less than the minimum value of the preset threshold range and the magnetization directions of all the magnetic steels are consistent, magnetizing the charging and demagnetizing magnetic steels; Alternatively, when the motor speed meets the preset threshold range, the magnet steel is not charged or demagnetized; Alternatively, when the motor speed is greater than the maximum value of the preset threshold range and the magnetization direction of the demagnetization magnetic steel is inconsistent with that of the other magnetic steels, the demagnetization magnetic steel is demagnetized.

3. The control method according to claim 2, characterized in that: When the demagnetizing magnetic steel is charged and demagnetized, a direct-axis pulse current is generated according to the motor speed and the current value to charge and demagnetize the demagnetizing magnetic steel, specifically including: When the demagnetized magnetic steel is demagnetized; The reverse direct-axis pulse current value is calculated by the following formula using the iteration method: n(k+1)=p×n(k)-q2×i(k); i(k)=i inv (k)-i d (k); Wherein, n(k+1) is the motor speed at time k+1, p is the torque pulsation, n(k) is the motor speed at time k, q2 is the magnetization constant coefficient corresponding to the preset speed, i(k) is the winding current value at time k, i inv (k) is the supply current value at time k, i d (k) is the direct-axis pulse current at time k; Generate a direct-axis pulse current according to the reverse direct-axis pulse current value and convert it into alternating current; The alternating current and the power supply current of the permanent magnet synchronous motor are synthesized and output to the permanent magnet synchronous motor.

4. The control method according to any one of claims 1 to 3, characterized in that: The obtaining of the motor speed and current value of the permanent magnet synchronous motor specifically includes: Obtaining a rotor position of the permanent magnet synchronous motor; Performing differentiation processing on the rotor position to obtain the motor speed of the permanent magnet synchronous motor; Obtaining a winding current value of the permanent magnet synchronous motor; A supply current value and a direct-axis pulse current are obtained according to the winding current value.

5. A control system for variable magnetic flux of a permanent magnet synchronous motor, wherein the rotor permanent magnet of the permanent magnet synchronous motor comprises a plurality of magnetic steels, wherein the magnetic steels comprise at least one magnetizing and demagnetizing magnetic steel made of a low coercive force permanent magnet material; characterized in that: The control system comprises: A current conditioning circuit connected to the permanent magnet synchronous motor for obtaining a current value of the permanent magnet synchronous motor; A speed analyzer disposed at a corresponding position of the permanent magnet synchronous motor for detecting the motor speed of the permanent magnet synchronous motor; A flux observer connected to the current conditioning circuit and the speed analyzer respectively, wherein the flux observer confirms the magnetization direction of each magnetic steel according to the current value and the motor speed; A processor connected to the flux observer and the speed analyzer respectively, the processor confirming whether to charge and demagnetize the charging and demagnetizing magnetic steel according to the motor speed and the magnetization direction of each magnetic steel; A charging and demagnetizing converter connected to the power supply circuit of the permanent magnet synchronous motor and the processor respectively; The charging and demagnetizing converter is specifically used for magnetizing the charging and demagnetizing magnetic steel; The forward direct-axis pulse current value is calculated by the following formula using the iteration method: n(k+1)=p×n(k)+q1×i(k); i(k)=i inv (k)+i d (k); Wherein, n(k+1) is the motor speed at time k+1, p is the torque pulsation, n(k) is the motor speed at time k, q1 is the magnetization constant coefficient corresponding to the preset speed, i(k) is the winding current value at time k, i inv (k) is the supply current value at time k, i d (k) is the direct-axis pulse current at time k; Generating a direct-axis pulse current according to the positive direct-axis pulse current value and converting it into alternating current; The alternating current and the power supply current of the permanent magnet synchronous motor are synthesized and output to the permanent magnet synchronous motor.

6. The control system according to claim 5, characterized in that: The processor includes: a judger and a calculator; The judger is respectively connected to the current conditioning circuit, the speed analyzer, and the calculator; The calculator is connected to the charging and demagnetizing converter.

7. The control system according to claim 6, characterized in that: The speed analyzer comprises: a position sensor and a speed analyzer; The position sensor is connected to the speed analyzer; The speed analyzer is connected to the flux observer and the processor respectively.

8. The control system according to claim 7, characterized in that: The charging and demagnetizing converter comprises: a pulse current exciter and a function generator; The processor, the pulse current exciter, the function generator, and the power supply circuit of the permanent magnet synchronous motor are connected in sequence.

9. The control system according to claim 8, characterized in that: The control system also includes: an inverter, a speed regulator and a drive circuit; The speed analyzer, the speed regulator, the drive circuit, the inverter, the power supply circuit of the permanent magnet synchronous motor, and the permanent magnet synchronous motor are connected in sequence.

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