Method, device, medium, controller and program product for demagnetization protection of an electric machine

Abstract

The application provides a demagnetization protection method, device, medium, controller and program product of a motor, and the method comprises the following steps: acquiring a torque-current ratio of the motor at a set motor temperature, a permanent magnet flux linkage value of the motor at the set motor temperature, and a permanent magnet flux linkage value of the motor at a current motor temperature; calculating a torque difference corresponding to a temperature difference between the current motor temperature and the set motor temperature according to the permanent magnet flux linkage value of the motor at the current motor temperature and the permanent magnet flux linkage value at the set motor temperature; judging whether irreversible demagnetization of the motor occurs according to the acquired torque-current ratio and the calculated torque difference; and if it is judged that irreversible demagnetization of the motor occurs, reducing a maximum current value limit of a controller output to perform demagnetization protection on the motor. The application can prevent the permanent magnet of the motor from further undergoing irreversible demagnetization when working in a strong reverse magnetic field after irreversible demagnetization occurs.

Description

TECHNICAL FIELD

[0001] The present application relates to the control field, and particularly to a demagnetization protection method and device of a motor, a medium, a controller and a program product. BACKGROUND

[0002] With the increasing attention to environmental protection and energy efficient utilization, the tide of automobile electrification is becoming more and more turbulent. For new energy vehicles, battery technology, motor technology and motor controller technology are known as the key three-electricity technology of new energy vehicles. Under the premise that the current battery technology has not made a breakthrough, improving the efficiency, power density, safety and reliability of the motor drive system has become the main research direction of the new energy vehicle motor drive system.

[0003] Permanent magnet assisted synchronous reluctance motor is widely used in pure electric or hybrid new energy vehicle field because of its high power density, wide speed range, small size and high efficiency. Compared with other types of motors, permanent magnet motor has some insurmountable advantages, but also has some disadvantages. Since the magnetic steel material commonly used by the permanent magnet assisted synchronous reluctance motor is ferrite, the magnetic steel residual magnetism density and coercive force of the material is small, and irreversible demagnetization is easy to occur, which affects the normal operation of the motor.

[0004] When the permanent magnet assisted synchronous reluctance motor works in a strong inverse magnetic field, high temperature and other harsh conditions, the permanent magnet in the motor may undergo irreversible demagnetization, resulting in a decline in motor performance. When the motor undergoes irreversible demagnetization, the permanent magnet in the motor continues to work in a strong inverse magnetic field, which will cause the permanent magnet to further undergo irreversible demagnetization, resulting in a significant decline in motor torque and affecting the output performance of the motor. In severe cases, it may even damage the entire drive system and affect the safety and reliability of the motor drive system. SUMMARY

[0005] The main purpose of the present application is to overcome the defects of the above-mentioned related technology, and provide a demagnetization protection method and device of a motor, a medium, a controller and a program product, to solve the problem that after the permanent magnet assisted synchronous reluctance motor undergoes irreversible demagnetization, the permanent magnet in the motor continues to work in a strong inverse magnetic field, which will cause the permanent magnet to further undergo irreversible demagnetization.

[0006] The application provides a demagnetization protection method of an electric machine, comprising: obtaining a torque-current ratio of the electric machine at a set electric machine temperature, a permanent magnet flux linkage value of the electric machine at the set electric machine temperature, and a permanent magnet flux linkage value of the electric machine at a current electric machine temperature; calculating a torque difference corresponding to a temperature difference between the current electric machine temperature and the set electric machine temperature according to the permanent magnet flux linkage value of the electric machine at the current electric machine temperature and the permanent magnet flux linkage value of the electric machine at the set electric machine temperature; judging whether irreversible demagnetization of the electric machine occurs according to the obtained torque-current ratio of the electric machine and the calculated torque difference; and reducing a maximum current output limit value of a controller of the electric machine to protect the electric machine from demagnetization if it is judged that irreversible demagnetization of the electric machine occurs.

[0007] Optionally, the permanent magnet flux linkage value of the electric machine at the current electric machine temperature is obtained by:

[0008] The permanent magnet flux linkage value of the electric machine at the current electric machine temperature is calculated according to the current electric machine temperature and the permanent magnet flux linkage value of the electric machine at the set electric machine temperature.

[0009] Optionally, the torque difference corresponding to the temperature difference between the current electric machine temperature and the set electric machine temperature is calculated according to the permanent magnet flux linkage value of the electric machine at the current electric machine temperature and the permanent magnet flux linkage value of the electric machine at the set electric machine temperature, comprising: calculating the torque difference corresponding to the temperature difference between the current electric machine temperature and the set electric machine temperature according to the permanent magnet flux linkage value of the electric machine at the current electric machine temperature, the permanent magnet flux linkage value of the electric machine at the set electric machine temperature, and a current q-axis current of the electric machine according to the following calculation formula:

[0010]

[0011] wherein, ΔT is the torque difference corresponding to the temperature difference between the current electric machine temperature and the set electric machine temperature, P is the number of pole pairs of the electric machine, ψ t is the permanent magnet flux linkage value of the electric machine when the electric machine temperature is t, is the permanent magnet flux linkage value of the electric machine when the electric machine temperature is the set electric machine temperature t0, i q is the current q-axis current of the electric machine.

[0012] Optionally, whether irreversible demagnetization of the electric machine occurs is judged according to the obtained torque-current ratio of the electric machine and the calculated torque difference, comprising: judging whether the unit current output torque of the electric machine is reduced and whether the reduction ratio is greater than or equal to a preset ratio value according to the torque-current ratio and the torque difference; and if it is judged that the unit current output torque of the electric machine is reduced and the reduction ratio is greater than or equal to the preset ratio value, it is determined that irreversible demagnetization of the electric machine occurs.

[0013] Optionally, if it is determined that irreversible demagnetization occurs in the motor, reducing the maximum current limit value output by the motor controller includes: reducing the maximum current limit value output by the motor controller according to the amount of reduction in the unit current output torque of the motor, wherein the reduction value ΔImax of the maximum current limit value output by the motor controller is obtained according to the following formula:

[0014]

[0015] Wherein, Imax is the maximum current limit value output by the controller of the motor before reduction, T0 is the output torque of the motor under the current working condition, and I0 is the motor current under the current working condition.

[0016] On the other hand, the present invention provides a demagnetization protection device for a motor, comprising: an acquisition unit for acquiring the torque-current ratio of the motor at a set motor temperature, the permanent magnet flux value of the motor at the set motor temperature, and the permanent magnet flux value of the motor at the current motor temperature; a calculation unit for calculating the torque difference corresponding to the temperature difference between the current motor temperature and the set motor temperature based on the permanent magnet flux value of the motor at the current motor temperature and the permanent magnet flux value of the motor at the set motor temperature; a judgment unit for judging whether irreversible demagnetization has occurred in the motor based on the acquired torque-current ratio of the motor and the calculated torque difference; and a protection unit for reducing the maximum current value limit value output by the motor controller if the demagnetization judgment unit judges that irreversible demagnetization has occurred in the motor, so as to perform demagnetization protection on the motor.

[0017] Optionally, the acquisition unit acquires the permanent magnet flux value of the motor at the current motor temperature, including: calculating the permanent magnet flux value of the motor at the current motor temperature based on the current motor temperature and the permanent magnet flux value of the motor at the set motor temperature.

[0018] Optionally, the calculation unit calculates the torque difference corresponding to the temperature difference between the current motor temperature and the set motor temperature based on the permanent magnet flux value of the motor at the current motor temperature and the permanent magnet flux value of the motor at the set motor temperature, including: calculating the torque difference corresponding to the temperature difference between the current motor temperature and the set motor temperature according to the following calculation formula based on the permanent magnet flux value of the motor at the current motor temperature, the permanent magnet flux value of the motor at the set motor temperature, and the current quadrature-axis current of the motor:

[0019]

[0020] Wherein, ΔT is the torque difference corresponding to the temperature difference between the current motor temperature and the set motor temperature, P is the motor pole pair number, ψ t is the permanent magnet flux linkage value of the motor when the motor temperature is t, is the permanent magnet flux linkage value of the motor when the motor temperature is the set motor temperature t0, i q is the current q-axis current of the motor.

[0021] Optionally, the judging unit judges whether the motor has irreversible demagnetization according to the torque-current ratio of the motor obtained and the torque difference calculated, and the method comprises: judging whether the unit current output torque of the motor is reduced and whether the reduction ratio is greater than or equal to a preset ratio value according to the torque-current ratio and the torque difference; if it is judged that the unit current output torque of the motor is reduced and the reduction ratio is greater than or equal to the preset ratio value, it is determined that the motor has irreversible demagnetization.

[0022] Optionally, the protection unit reduces the controller output maximum current value limit of the motor if the demagnetization judging unit judges that the motor has irreversible demagnetization, and the method comprises: reducing the controller output maximum current value limit of the motor according to the reduction amount of the unit current output torque of the motor, wherein the reduction value ΔImax of the controller output maximum current value limit of the motor is obtained according to the following formula:

[0023]

[0024] Wherein, Imax is the controller output maximum current value limit of the motor before reduction, T0 is the output torque of the motor under the current working condition, and I0 is the motor current under the current working condition.

[0025] In still another aspect, the present application provides a storage medium having a computer program stored thereon, wherein the program, when executed by a processor, implements the steps of any of the aforementioned methods.

[0026] In still another aspect, the present application provides a motor controller comprising a processor, a memory, and a computer program stored on the memory and executable on the processor, wherein the processor implements the steps of any of the aforementioned methods when executing the program.

[0027] In still another aspect, the present application provides a motor controller comprising the demagnetization protection device of any of the aforementioned motor.

[0028] In still another aspect, the present application provides a computer program product comprising a computer program, wherein the computer program, when executed by a processor, implements the steps of any of the aforementioned methods.

[0029] According to the technical scheme of the application, when irreversible demagnetization occurs in the motor, the maximum current value limit value output by the controller is reduced to prevent the permanent magnet in the motor from continuously working in a strong demagnetizing field condition and further irreversible demagnetization occurs, and the safety and reliability of the motor are ensured.

[0030] According to the technical scheme of the application, the torque difference generated by the motor temperature difference is calculated, and whether irreversible demagnetization occurs in the motor is judged according to the actual torque difference value output by the motor and the calculated torque difference, and the influence of reversible demagnetization of the motor on the protection strategy judgment is excluded. If it is judged that irreversible demagnetization occurs in the motor, the maximum current value limit value output by the controller is reduced according to the demagnetization degree to prevent the motor from further irreversible demagnetization, and more serious failure of the entire drive system is avoided. BRIEF DESCRIPTION OF DRAWINGS

[0031] The drawings described herein are used to provide further understanding of the application, and form a part of the application. The illustrative embodiments of the application and their descriptions serve to explain the application, and do not constitute an improper limitation on the application. In the drawings:

[0032] Figure 1 is a method schematic diagram of an embodiment of the demagnetization protection method of the motor provided by the application;

[0033] Figure 2 shows a schematic diagram of the change of the residual magnetism of the ferrite with temperature;

[0034] Figure 3 is a method schematic diagram of a specific embodiment of the demagnetization protection method of the motor provided by the application;

[0035] Figure 4 is a structure block diagram of an embodiment of the demagnetization protection device of the motor provided by the application. DETAILED DESCRIPTION

[0036] To make the purpose, technical scheme and advantages of the application more clear, the technical scheme of the application will be described clearly and completely below by combining the specific embodiments of the application and corresponding drawings. Obviously, the described embodiments are only some of the embodiments of the application, but not all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the application.

[0037] It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting, unless the context clearly indicates so. It will be further understood that the use of relational terms such as first and second, and the like are used solely to distinguish one from another entity without necessarily implying a relationship or order between these entities. Moreover, the terms "comprises", "comprising", "includes", "including", "has", "having" or any other variation thereof, are intended to cover a non-exclusive inclusion, for example, a process, method, article, or apparatus that comprises, but is not limited to, a list of steps or elements as explicitly set forth. None of the above terms require that any or all of the steps or elements listed to occur or be present.

[0038] The permanent magnet of the ferrite material has a large specific temperature coefficient, the residual magnetism of the permanent magnet is greatly affected by temperature, and reversible demagnetization exists when the motor is running. Figure 2 A schematic diagram showing the change of the residual magnetism of the ferrite with temperature is shown. The horizontal axis represents temperature, unit: ℃, and the vertical axis represents the residual magnetism Br of the permanent magnet, unit: tesla.

[0039] Reversible demagnetization generally refers to the decrease of the flux linkage of the permanent magnet in the motor due to the increase of temperature, but when the temperature returns to normal temperature, the flux linkage of the permanent magnet returns to the original size. Irreversible demagnetization refers to that the permanent magnet is in a strong reverse magnetic field, resulting in irreversible decrease of the flux linkage of the permanent magnet.

[0040] The present application provides a demagnetization protection method of a motor. The method is particularly suitable for a permanent magnet assisted synchronous reluctance motor.

[0041] Figure 1 The present application provides a method schematic diagram of an embodiment of the demagnetization protection method of the motor.

[0042] As shown in Figure 1 According to an embodiment of the present application, the demagnetization protection method of the motor at least includes steps S110, S120, S130 and S140.

[0043] In step S110, the torque-current ratio of the motor at a set motor temperature, the permanent magnet flux linkage value of the motor at the set motor temperature and the permanent magnet flux linkage value of the motor at the current motor temperature are obtained.

[0044] The torque-current ratio of the motor is the ratio of the output torque of the motor to the controller output current of the motor. Specifically, the motor is calibrated first, and the controller output current of the motor under different working conditions is collected. The different working conditions include different motor speeds and torques. The torque-current ratio T / I of the motor at a set motor temperature and the permanent magnet flux linkage value ψ of the motor at the set motor temperature t0 are collected.t0 T represents the output torque of the motor, and I represents the current of the motor. The set motor temperature is, for example, 25℃.

[0045] In one embodiment, the permanent magnet flux linkage value of the motor at the current motor temperature is obtained by calculating the permanent magnet flux linkage value of the motor at the current motor temperature according to the current motor temperature and the permanent magnet flux linkage value of the motor at the set motor temperature.

[0046] Specifically, the motor temperature under any working condition is collected, and the permanent magnet flux linkage value of the motor at the current motor temperature is calculated according to the current collected motor temperature and the permanent magnet flux linkage value of the motor at the set motor temperature t0 The permanent magnet flux linkage value of the motor at the current motor temperature is calculated. In one embodiment, the permanent magnet flux linkage value of the motor at the current motor temperature is calculated according to the current motor temperature and the permanent magnet flux linkage value of the motor at the set motor temperature according to the following formula:

[0047]

[0048] Wherein, ψ t is the permanent magnet flux linkage value of the motor when the motor temperature is t, is the permanent magnet flux linkage value of the motor when the motor temperature is the set motor temperature t0, and a is the specific temperature coefficient of the permanent magnet, for example, -0.18% / ℃.

[0049] Step S120, according to the permanent magnet flux linkage value of the motor at the current motor temperature and the permanent magnet flux linkage value of the motor at the set motor temperature, the torque difference corresponding to the temperature difference between the current motor temperature and the set motor temperature is calculated.

[0050] The torque difference corresponding to the temperature difference between the current motor temperature and the set motor temperature, that is, the torque difference generated by the temperature difference between the current motor temperature and the set motor temperature. In one embodiment, the torque difference corresponding to the temperature difference between the current motor temperature and the set motor temperature is calculated according to the permanent magnet flux linkage value of the motor at the current motor temperature, the permanent magnet flux linkage value of the motor at the set motor temperature and the current q-axis current of the motor according to the following calculation formula:

[0051]

[0052] Wherein, ΔT is the torque difference corresponding to the temperature difference between the current motor temperature and the set motor temperature, P is the number of motor pole pairs, ψ t is the permanent magnet flux linkage value of the motor when the motor temperature is t, is the permanent magnet flux linkage value of the motor when the temperature of the motor is the set motor temperature t0, i q is the current q-axis current of the motor.

[0053] Step S130, according to the acquired torque-current ratio of the motor and the calculated torque difference, it is judged whether the motor irreversible demagnetization occurs.

[0054] In a specific embodiment, according to the torque-current ratio and the torque difference, it is judged whether the motor unit current output torque is reduced, and the reduction ratio is greater than or equal to a preset ratio value; if it is judged that the motor unit current output torque is reduced and the reduction ratio is greater than or equal to the preset ratio value, it is determined that the motor irreversible demagnetization occurs; if it is judged that the motor unit current output torque is not reduced or the reduction value is less than the preset ratio value, it is determined that the motor operating condition is normal, and no processing is performed.

[0055] Specifically, the motor unit current output torque is equal to (T0+ΔT) / I0; the motor unit current output torque reduction value is T / I-(T0+ΔT) / I0, and the reduction ratio of the motor unit current output torque is Wherein, T0 is the output torque of the motor under the current working condition, and I0 is the motor current under the current working condition. Let the preset ratio value be a, that is, it is judged whether (T0+ΔT) / I0 If not, that is, (T0+ΔT) / I0≥T / I, or It is determined that the motor operating condition is normal, and the controller does not process. If (T0+ΔT) / I0 That is, the unit current output torque is reduced, and the reduction ratio exceeds the preset ratio value a, it is determined that the motor irreversible demagnetization occurs.

[0056] According to the above embodiment, whether the motor irreversible demagnetization occurs is judged by whether the motor flux linkage is reduced. The motor flux linkage value is reduced by more than a preset ratio value (the value range of the preset ratio value includes, for example, 1.5%~3%, for example, 1.5%, that is, 0.015), and it is determined that the motor irreversible demagnetization occurs. The motor unit current output torque T / I is proportional to the motor flux linkage, so whether the motor irreversible demagnetization occurs is judged according to the degree of reduction of the motor unit current output torque T / I.

[0057] Step S140, if it is judged that the motor irreversible demagnetization occurs, the controller output maximum current value limit value of the motor is reduced to perform demagnetization protection on the motor.

[0058] Specifically, if it is determined that the motor has irreversible demagnetization, the controller output maximum current value limit value of the motor is reduced according to the reduction of the unit current output torque of the motor, to prevent the motor from further irreversible demagnetization.

[0059] In a specific embodiment, the reduction value ΔImax of the controller output maximum current value limit value of the motor is obtained according to the following formula:

[0060]

[0061] That is, the controller output maximum current value limit value of the motor is set to I max -ΔI max ; wherein Imax is the controller output maximum current value limit value of the motor before reduction, and ΔImax is the reduction value of the controller output maximum current value limit value of the motor:

[0062]

[0063] Wherein T0 is the motor torque of the motor under the current working condition, and I0 is the motor current under the current working condition, that is, T0 and I0 are the motor torque and motor current of the motor under any working condition, respectively. That is, T0 is the motor torque of the motor under any working condition, and I0 is the motor current under the same working condition (the same working condition as T0).

[0064] For example, if the unit current output torque is reduced by more than 1.5%, it is determined that the motor has irreversible demagnetization, and the controller MCU of the motor reduces the controller output maximum current value limit value of the controller output according to the reduction amount of the unit current output torque That is, the controller output maximum current value limit value of the controller output is set to I max -ΔI max to prevent the motor from further irreversible demagnetization. Preferably, after reducing the controller output maximum current value limit value of the motor, the torque-current ratio T / I of the motor is updated to determine again whether the motor has irreversible demagnetization and to perform demagnetization protection.

[0065] According to the above embodiment of the application, the difference between the motor permanent magnet fluxes at two different temperatures is calculated according to the motor temperature difference, so as to calculate the torque difference caused by the motor temperature difference (i.e. reversible demagnetization of the motor). The actual motor output torque difference is compared with the calculated torque difference, and if the actual motor output torque difference is greater than the calculated torque difference, it is determined that the motor has irreversible demagnetization. The influence of reversible demagnetization of the motor on the protection strategy is excluded, and if it is determined that the motor has irreversible demagnetization, the controller output maximum current value limit value is reduced according to the demagnetization degree, to prevent the motor from further irreversible demagnetization.

[0066] To make the technical scheme of the present application clear, the execution flow of the demagnetization protection method of the motor provided by the present application is described below with one specific embodiment.

[0067] Figure 3 is a method schematic diagram of one specific embodiment of the demagnetization protection method of the motor provided by the present application. As shown in Figure 3

[0068] Step 1: calibrate the motor, and collect the torque-current ratio T / I of the motor at a certain temperature;

[0069] Step 2: collect the temperature of the motor under any working condition of the motor, and calculate the flux of the permanent magnet of the motor at the temperature, For example, t0 is 25℃, then ψ t = ψ 25℃ × [1+α(t-25℃)].

[0070] Step 3: calculate the torque difference ΔT due to the temperature difference of the motor: ΔT = P(ψ 25℃ - ψ t )i q .

[0071] Step 4: determine whether the unit current output torque of the motor is reduced, that is, whether the following condition is met:

[0072] (T0+ΔT) / I0 < T / I, and

[0073] Step 5: if the unit current output torque of the motor is not reduced or is reduced less, that is, (T0+ΔT) / I0 ≥ T / I, or the motor is in normal operation, and the controller does not process.

[0074] if the unit current output torque of the motor is reduced, that is, (T0+ΔT) / I0 < T / I, and that is, the unit current output torque is reduced by more than 1.5%, it is determined that the motor has occurred irreversible demagnetization, and the driving motor controller MCU reduces the maximum current value limit of the controller output according to the amount of reduction of the unit current output torque that is, the maximum current value limit of the controller output of the controller is set to I max - ΔI max , to prevent the motor from further irreversible demagnetization; at the same time, the torque-current ratio T / I of the motor is updated, and the process returns to step S2.

[0075] The present application also provides a demagnetization protection device for a motor. The device is particularly suitable for a permanent magnet auxiliary synchronous reluctance motor.

[0076] Figure 4 ​is a structural block diagram of an embodiment of the demagnetization protection device of the motor provided by the present application. As shown in Figure 4 the demagnetization protection device 100 of the motor includes an acquisition unit 110, a calculation unit 120, a judgment unit 130, and a protection unit 140.

[0077] The acquisition unit 110 is configured to acquire a torque-current ratio of the motor at a set motor temperature, a permanent magnet flux linkage value of the motor at the set motor temperature, and a permanent magnet flux linkage value of the motor at a current motor temperature.

[0078] The torque-current ratio of the motor is a ratio of an output torque of the motor to a controller output current of the motor. Specifically, the motor is calibrated first, and the controller output current of the motor at different operating conditions is collected. The different operating conditions include different motor speeds and torques. The torque-current ratio T / I of the motor at the set motor temperature and the permanent magnet flux linkage value ψ t0 of the motor at the set motor temperature t0 are collected. T represents the output torque of the motor, and I represents the current of the motor. The set motor temperature is, for example, 25°C.

[0079] In one specific embodiment, the acquisition unit 110 acquires the permanent magnet flux linkage value of the motor at the current motor temperature, including: calculating the permanent magnet flux linkage value of the motor at the current motor temperature according to the current motor temperature and the permanent magnet flux linkage value of the motor at the set motor temperature.

[0080] Specifically, the motor temperature at any operating condition is collected, and the permanent magnet flux linkage value of the motor at the current motor temperature is calculated according to the currently collected motor temperature and the permanent magnet flux linkage value ψ of the motor at the set motor temperature t0. In one specific embodiment, the permanent magnet flux linkage value of the motor at the current motor temperature is calculated according to the current motor temperature and the permanent magnet flux linkage value of the motor at the set motor temperature, according to the following formula:

[0081]

[0082] wherein ψ t is the permanent magnet flux linkage value of the motor when the motor temperature is t, is the permanent magnet flux linkage value of the motor when the motor temperature is the set motor temperature t0, and α is the specific temperature coefficient of the permanent magnet, for example, -0.18% / °C.

[0083] The calculation unit 120 is configured to calculate a torque difference corresponding to a temperature difference between the current motor temperature and the set motor temperature according to the permanent magnet flux linkage value of the motor at the current motor temperature and the permanent magnet flux linkage value of the motor at the set motor temperature.

[0084] a torque difference corresponding to a temperature difference between the current motor temperature and the set motor temperature, i.e., a torque difference caused by a temperature difference between the current motor temperature and the set motor temperature. In one specific embodiment, the torque difference corresponding to the temperature difference between the current motor temperature and the set motor temperature is calculated according to a permanent magnet flux linkage value of the motor at the current motor temperature, a permanent magnet flux linkage value of the motor at the set motor temperature, and a current q-axis current of the motor, according to the following calculation formula:

[0085]

[0086] wherein ΔT is the torque difference corresponding to the temperature difference between the current motor temperature and the set motor temperature, P is a pole pair number of the motor, ψ t is the permanent magnet flux linkage value of the motor when the motor temperature is t, is the permanent magnet flux linkage value of the motor when the motor temperature is the set motor temperature t0, and i q is the current q-axis current of the motor.

[0087] The judging unit 130 is configured to judge whether the motor has irreversible demagnetization according to the obtained torque current ratio of the motor and the calculated torque difference.

[0088] In one specific embodiment, it is judged according to the torque current ratio and the torque difference whether the unit current output torque of the motor is reduced and whether the reduction ratio is greater than or equal to a preset ratio value; if it is judged that the unit current output torque of the motor is reduced and the reduction ratio is greater than or equal to the preset ratio value, it is determined that the motor has irreversible demagnetization; if it is judged that the unit current output torque of the motor is not reduced or the reduction value is less than the preset ratio value, it is determined that the motor is in normal operation and no processing is performed.

[0089] Specifically, the unit current output torque of the motor is equal to (T0+ΔT) / I0; the reduction value of the unit current output torque of the motor is equal to T / I-(T0+ΔT) / I0, and the reduction ratio of the unit current output torque of the motor is wherein T0 is the output torque of the motor under the current working condition, and I0 is the motor current under the current working condition. It is assumed that the preset ratio value is a, i.e., it is judged whether (T0+ΔT) / I0 If it is not satisfied, i.e., (T0+ΔT) / I0≥T / I, or it is determined that the motor is in normal operation and the controller does not perform processing. If (T0+ΔT) / I0 i.e., the unit current output torque is reduced and the reduction ratio exceeds the preset ratio value a, it is determined that the motor has irreversible demagnetization.

[0090] According to the above embodiment, whether the motor is irreversible demagnetized is determined by whether the motor flux linkage is reduced, and the motor flux linkage value is reduced by more than a preset proportion (for example, the value range of the preset proportion includes 1.5% to 3%, for example, 1.5%, that is, 0.015), and it is determined that the motor is irreversible demagnetized. The motor unit current output torque T / I is proportional to the motor flux linkage, so whether the motor is irreversible demagnetized is determined according to the degree of reduction of the motor unit current output torque T / I.

[0091] The protection unit 140 is configured to reduce the controller output maximum current value limit of the motor to protect the motor from demagnetization if the demagnetization determination unit determines that the motor is irreversible demagnetized.

[0092] Specifically, if it is determined that the motor is irreversible demagnetized, the controller output maximum current value limit of the motor is reduced according to the reduction of the motor unit current output torque to prevent the motor from further irreversible demagnetization.

[0093] In a specific embodiment, the reduction value ΔImax of the controller output maximum current value limit of the motor is obtained according to the following formula:

[0094]

[0095] That is, the controller output maximum current value limit of the motor is set to I max -ΔI max ; wherein Imax is the controller output maximum current value limit of the motor before reduction, and ΔImax is the reduction value of the controller output maximum current value limit of the motor:

[0096]

[0097] Wherein T0 is the motor torque of the motor under the current working condition, and I0 is the motor current under the current working condition, that is, T0 and I0 are the motor torque and motor current of the motor under any working condition, respectively. That is, T0 is the motor torque of the motor under any working condition, and I0 is the motor current under the same working condition (the same working condition as T0).

[0098] For example, if the unit current output torque is reduced by more than 1.5%, it is determined that the motor has been irreversible demagnetized, and the controller output maximum current value limit of the controller output is reduced by the MCU according to the reduction of the unit current output torque That is, the controller output maximum current value limit of the controller output is set to I max -ΔI maxPreferably, after reducing the maximum current value limit of the controller output of the motor, the torque-current ratio T / I of the motor is updated to determine again whether the irreversible demagnetization of the motor occurs, and the demagnetization protection is performed.

[0099] The application further provides a storage medium corresponding to the demagnetization protection method of the motor, which stores a computer program, and the computer program is executed by a processor to implement the steps of any of the above methods.

[0100] The application further provides a motor controller corresponding to the demagnetization protection method of the motor, which comprises a processor, a memory, and a computer program stored in the memory and executable on the processor, and the processor executes the computer program to implement the steps of any of the above methods.

[0101] The application further provides a motor controller corresponding to the demagnetization protection device of the motor, which comprises the demagnetization protection device of the motor as any of the above.

[0102] The application further provides a computer program product corresponding to the demagnetization protection method of the motor, which comprises a computer program, and the computer program is executed by a processor to implement the steps of any of the above methods.

[0103] According to the application, when the irreversible demagnetization of the motor occurs, the maximum current value limit of the controller output is reduced to prevent the permanent magnet in the motor from continuing to work in a strong reverse magnetic field and further causing irreversible demagnetization, thereby ensuring the safety and reliability of the motor.

[0104] According to the technical scheme of the application, the torque difference caused by the temperature difference of the motor is calculated, and the actual torque difference of the motor and the calculated torque difference are compared to determine whether the irreversible demagnetization of the motor occurs, thereby eliminating the influence of the reversible demagnetization of the motor on the protection strategy. If the irreversible demagnetization of the motor is determined, the maximum current value limit of the controller output is reduced according to the demagnetization degree to prevent the irreversible demagnetization of the motor from further occurring, thereby avoiding more serious failure of the entire drive system.

[0105] The functions described herein can be implemented in hardware, software executed by a processor, firmware, or any combination thereof. If implemented in software executed by a processor, the functions can be stored on or transferred over as one or more instructions or code on a computer-readable medium. Other examples and implementations are within the scope and spirit of the disclosure and appended claims. For example, due to the nature of software, functions described above can be implemented using software executed by a processor, hardware, firmware, hardwiring, or combinations of any of these. Features implementing functions can also be physically located at various positions, including being distributed such that portions of functions are implemented at different physical locations. Also, as used herein, including in the claims, "or" as used in a list of items prefaced by "comprising" to indicate a disjunctive list means each individual item can be present or none can be present, but that a listing of two or more items do not require that any or all of the items be present, and that the

[0106] In several embodiments provided in the present application, it should be understood that the disclosed technology can be implemented in other ways. Among them, the above-mentioned device embodiments are only schematic, for example, the division of the units can be a logical function division, and other division manners can be used in actual implementation, for example, a plurality of units or components can be combined or integrated into another system, or some features can be ignored or not executed. In addition, the coupling or direct coupling or communication connection between the displayed or discussed units can be indirect coupling or communication connection through some interfaces, units or modules, and can be electrical or other forms.

[0107] The units described as separate components can or can not be physically separated, and the components of the control device can or can not be physical units, i.e. can be located in one place or can be distributed on a plurality of units. Part or all of the units can be selected according to actual needs to achieve the purpose of the embodiment.

[0108] The integrated unit, if implemented in the form of a software function unit and sold or used as an independent product, can be stored in a computer readable storage medium. Based on such understanding, the technical solutions of the present application essentially or the part that contributes to the related art or the whole or part of the technical solutions can be embodied in the form of a software product. The computer software product is stored in a storage medium, including a plurality of instructions for causing a computer device (which can be a personal computer, a server or a network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of the present application. The aforementioned storage medium includes: a U disk, a read-only memory (ROM, Read-Only Memory), a random access memory (RAM, Random Access Memory), a mobile hard disk, a magnetic disk or an optical disk, and various media that can store program codes.

[0109] The above merely illustrates the embodiments of the present application but should not be taken as limitations. Various changes and modifications can be made by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the scope of claims of the present application.

Claims

1. A demagnetization protection method of an electric machine, characterized by, The method comprises the following steps: acquiring a torque-current ratio of the motor at a set motor temperature, a permanent magnet flux linkage value of the motor at the set motor temperature, and a permanent magnet flux linkage value of the motor at a current motor temperature; calculating a torque difference corresponding to a temperature difference between the current motor temperature and the set motor temperature according to the permanent magnet flux linkage value of the motor at the current motor temperature and the permanent magnet flux linkage value of the motor at the set motor temperature; judging whether irreversible demagnetization of the motor occurs according to the acquired torque-current ratio of the motor and the calculated torque difference, comprising: judging whether the unit current output torque of the motor decreases and whether the decrease ratio is greater than or equal to a preset ratio value according to the torque-current ratio and the torque difference; if it is judged that the unit current output torque of the motor decreases and the decrease ratio is greater than or equal to the preset ratio value, it is determined that irreversible demagnetization of the motor occurs; if it is judged that irreversible demagnetization of the motor occurs, reducing a controller output maximum current value limit of the motor to perform demagnetization protection on the motor.

2. The method of claim 1, wherein, The method comprises the following steps: acquiring a permanent magnet flux linkage value of the motor at a current motor temperature, comprising:

3. The method of claim 1, wherein, calculating the permanent magnet flux linkage value of the motor at the current motor temperature according to the current motor temperature and the permanent magnet flux linkage value of the motor at the set motor temperature. calculating a torque difference corresponding to a temperature difference between the current motor temperature and the set motor temperature according to the permanent magnet flux linkage value of the motor at the current motor temperature and the permanent magnet flux linkage value of the motor at the set motor temperature, comprising: Wherein, ΔT is the torque difference corresponding to the temperature difference between the current motor temperature and the set motor temperature, P is the number of motor pole pairs, ψ t is the permanent magnet flux value of the motor when the motor temperature is t, is the permanent magnet flux value of the motor when the motor temperature is the set motor temperature t0, i q is the current q-axis current of the motor.

4. The method of claim 1, wherein, calculating the torque difference corresponding to the temperature difference between the current motor temperature and the set motor temperature according to the permanent magnet flux linkage value of the motor at the current motor temperature, the permanent magnet flux linkage value of the motor at the set motor temperature, and the current q-axis current of the motor according to the following calculation formula: if it is judged that irreversible demagnetization of the motor occurs, reducing a controller output maximum current value limit of the motor, comprising: reducing the controller output maximum current value limit of the motor according to the decrease amount of the unit current output torque of the motor, wherein the reduction value ΔImax of the controller output maximum current value limit of the motor is obtained according to the following formula:

5. A demagnetization protection device for an electric machine, characterized by comprising: wherein, Imax is the controller output maximum current value limit of the motor before reduction, ΔT is the torque difference corresponding to the temperature difference between the current motor temperature and the set motor temperature, T / I is the unit current output torque of the motor, T0 and I0 are respectively the motor torque and motor current of the motor under any working condition. The method comprises the following steps: an acquiring unit, configured to acquire a torque-current ratio of the motor at a set motor temperature, a permanent magnet flux linkage value of the motor at the set motor temperature, and a permanent magnet flux linkage value of the motor at a current motor temperature; a calculating unit, configured to calculate a torque difference corresponding to a temperature difference between the current motor temperature and the set motor temperature according to the permanent magnet flux linkage value of the motor at the current motor temperature and the permanent magnet flux linkage value of the motor at the set motor temperature; The judging unit is configured to judge whether the motor is subjected to irreversible demagnetization according to the obtained torque-current ratio of the motor and the calculated torque difference, and comprises: judging whether the torque per unit current output of the motor is reduced and whether the reduction ratio is greater than or equal to a preset ratio value according to the torque-current ratio and the torque difference; and determining that the motor is subjected to irreversible demagnetization if the torque per unit current output of the motor is reduced and the reduction ratio is greater than or equal to the preset ratio value. The protection unit is configured to reduce the maximum current output value limit of the controller of the motor to perform demagnetization protection on the motor if the demagnetization judging unit judges that the motor is subjected to irreversible demagnetization.

6. The apparatus of claim 5, wherein, The obtaining unit obtains the permanent magnet flux linkage value of the motor at the current motor temperature, and comprises: calculating the permanent magnet flux linkage value of the motor at the current motor temperature according to the current motor temperature and the permanent magnet flux linkage value of the motor at the set motor temperature.

7. A storage medium, characterized by A computer program is stored on the computer program, and the program is executed by the processor to realize the steps of the method of any one of claims 1-4.

8. An electric machine controller characterized by The processor, the memory, and the computer program stored on the memory and executable on the processor are included, and the processor realizes the steps of the method of any one of claims 1-4 when executing the program, or the demagnetization protection device of the motor of any one of claims 5-6 is included.

9. A computer program product, characterised in that, The computer program is included, and the computer program is executed by the processor to realize the steps of the method of any one of claims 1-4.

Images