Motor control anti-demagnetization protection system and method

Abstract

The invention discloses an anti-demagnetization protection system and method for motor control. The method comprises the following steps: acquiring counter electromotive force of a motor winding and real-time counter electromotive force of each phase of winding of a motor under a fault-free condition; respectively subtracting the counter electromotive force of the motor winding under the fault-free condition from the real-time counter electromotive force of each phase winding of the motor to obtain the maximum difference value of the real-time counter electromotive force of the phase windings of the motor; and comparing the maximum difference value of the real-time counter electromotive force of the motor phase winding with a demagnetization fault threshold value to judge whether the motor is in a demagnetization fault, if the motor is not in the demagnetization fault state, the motor operates normally, and if the motor is in the demagnetization fault state, demagnetization protection is carried out. According to the invention, real-time on-line and high-sensitivity effective evaluation and identification can be carried out on the demagnetization fault degree and the fault mode of the motor.

Description

Technical Field

[0001] The present invention relates to the field of motor control anti-demagnetization, and in particular to a motor control anti-demagnetization protection system and method. Background Art

[0002] With the rapid development of electric vehicles in the future, permanent magnet synchronous motors are ushering in a period of faster development. They have been widely used due to their small size and high efficiency. As the main power source of hybrid electric vehicles and the only power source of pure electric vehicles, the operating performance and control quality of motors and their drive control systems directly affect the reliability and comfort of vehicle operation. However, due to the small internal space of the vehicle, heat dissipation difficulties, various complex operating conditions, strong electric drive reactions, and natural aging, local demagnetization or uniform demagnetization failures are prone to occur, resulting in reduced vehicle power and safety. At present, the commonly used demagnetization methods for motor control detection include model-based diagnosis, data-driven diagnosis based on current signals, diagnosis based on high-frequency signal injection, diagnosis based on high-frequency signal injection, etc., which are not suitable for online, real-time, high-sensitivity diagnosis of demagnetization faults and accurate assessment of the degree of demagnetization faults. Summary of the invention

[0003] The present invention provides a motor control anti-demagnetization protection system on the one hand, and a motor control anti-demagnetization protection method on the other hand. The system and method can realize real-time online and highly sensitive effective evaluation and identification of the degree and fault mode of demagnetization faults, and adopt effective fault-tolerant control strategies to reduce the influence of permanent magnet demagnetization faults on the operating performance of the electric drive system, thereby realizing safe and reliable operation of the electric drive system of electric vehicles.

[0004] To achieve this purpose, the present invention provides a motor control anti-demagnetization protection method, which includes:

[0005] Obtain the back EMF of the motor winding under fault-free conditions and the real-time back EMF of each phase winding of the motor;

[0006] The back EMF of the motor winding under fault-free conditions is subtracted from the real-time back EMF of each phase winding of the motor to obtain the maximum difference of the real-time back EMF of the motor phase winding;

[0007] The maximum real-time back-electromotive force difference of the motor phase winding is compared with the demagnetization fault threshold to determine whether the motor is in a demagnetization fault state. If the motor is not in a demagnetization fault state, the motor operates normally. If the motor is in a demagnetization fault state, demagnetization protection is performed.

[0008] Furthermore, the back EMF of the motor winding under fault-free conditions is obtained by calibration.

[0009] Furthermore, the method for obtaining the real-time back EMF of each phase winding of the motor includes: calculating the real-time back EMF of each coil in each phase winding of the motor, and adding the back EMFs of all coils in each phase winding to obtain the real-time back EMF of each phase winding of the motor.

[0010] Furthermore, the method for calculating the real-time back EMF of each coil in each phase winding of the motor includes: calculating the real-time back EMF of the coil in the incoming stator slot and the real-time back EMF of the coil in the outgoing stator slot of each coil, and obtaining the real-time back EMF of each coil in each phase winding of the motor by subtracting the real-time back EMF of the coil in the incoming stator slot from the real-time back EMF of the coil in the outgoing stator slot.

[0011] Furthermore, the method for calculating the real-time back EMF of the coil in the incoming stator slot and the real-time back EMF of the coil in the outgoing stator slot of each coil includes: the real-time back EMF of the coil in the incoming stator slot and the real-time back EMF of the coil in the outgoing stator slot of each coil are calculated based on the electrical angular frequency of the rotor operation, the back EMF coefficient of the coil in the stator slot and the slot angle of the motor.

[0012] Furthermore, the method for obtaining the electrical angular frequency of the rotor and the back electromotive force coefficient of the coil in the stator slot includes: obtaining the electrical angular frequency of the rotor and the back electromotive force coefficient of the coil in the stator slot according to the real-time speed of the motor.

[0013] Furthermore, the method for obtaining the maximum difference in real-time back EMF of the motor phase winding includes: subtracting the real-time back EMF of each phase winding of the motor from the back EMF of the winding under fault-free conditions corresponding to the current speed to obtain a set of differences, and taking the maximum value in the set of differences as the maximum difference in real-time back EMF of the motor phase winding.

[0014] Furthermore, the method for performing demagnetization protection based on the maximum difference in real-time back-EMF of the motor phase windings includes: judging the size of the maximum difference in real-time back-EMF of the motor phase windings and the demagnetization fault threshold; when the maximum difference in real-time back-EMF of the motor phase windings is less than the demagnetization fault threshold, the motor controller executes the current torque command normally, otherwise linear derating is performed.

[0015] A motor control anti-demagnetization protection system using the above motor control anti-demagnetization protection method comprises a back-electromotive force acquisition module and an anti-demagnetization protection module;

[0016] The back-EMF acquisition module is used to obtain the back-EMF of the motor winding under fault-free conditions and the real-time back-EMF of each phase winding of the motor;

[0017] The anti-demagnetization protection module is used to make a difference between the back EMF of the motor winding under fault-free conditions and the real-time back EMF of each phase winding of the motor, and obtain the maximum difference of the real-time back EMF of the motor phase winding;

[0018] The anti-demagnetization protection module is also used to compare the maximum difference in real-time back electromotive force of the motor phase winding with the demagnetization fault threshold to determine whether the motor is in a demagnetization fault state. When the motor is not in a demagnetization fault state, the motor runs normally. When the motor is in a demagnetization fault state, demagnetization protection is performed.

[0019] Beneficial effects of the present invention: The present invention determines to use the real-time back EMF of each phase winding as the characteristic quantity for local demagnetization fault detection through analysis of the relationship between the coil voltage of each phase winding and its back EMF, which greatly improves the detection sensitivity, implements reliable diagnosis of early demagnetization faults, and realizes real-time, online and high-precision effective evaluation and identification of the degree and fault mode of demagnetization faults, thereby realizing safe and reliable operation of the electric drive system of electric vehicles. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a flow chart of demagnetization fault detection of the present invention;

[0021] Figure 2 It is a structural schematic diagram of the present invention. DETAILED DESCRIPTION

[0022] The invention with publication number CN113030729A obtains the temporary no-load back electromotive force of the permanent magnet motor according to the signal output frequency on the stator winding side of the permanent magnet motor to be tested and the corresponding open-circuit voltage, and obtains the no-load back electromotive force of the permanent magnet motor to be tested according to the temporary no-load back electromotive force, temperature, temperature threshold, etc. of the permanent magnet motor, and compares the no-load back electromotive force with the pre-set standard no-load back electromotive force value of the permanent magnet motor to be tested. When the no-load back electromotive force is less than or equal to the standard no-load back electromotive force value, the demagnetization warning signal of the permanent magnet motor to be tested and the above-mentioned no-load back electromotive force are output. Although the invention can detect the motor demagnetization fault online, the sensitivity is relatively low. The present invention can achieve real-time and highly sensitive judgment of whether the motor is in a demagnetization fault by comparing the difference between the real-time back electromotive force of each phase winding and the motor back electromotive force under fault-free conditions with the demagnetization fault threshold. Please refer to Example 1 for the specific implementation method.

[0023] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments:

[0024] Example 1

[0025] Figure 1 The present invention is a flow chart of demagnetization fault detection of a motor control anti-demagnetization protection method according to an embodiment of the present invention. The motor control anti-demagnetization protection method is used to perform demagnetization detection and protection on the motor control anti-demagnetization. The motor control anti-demagnetization protection method includes:

[0026] Obtain the back EMF of the motor winding under fault-free conditions and the real-time back EMF of each phase winding of the motor;

[0027] The back EMF of the motor winding under fault-free conditions is subtracted from the real-time back EMF of each phase winding of the motor to obtain the maximum difference of the real-time back EMF of the motor phase winding;

[0028] The maximum real-time back-electromotive force difference of the motor phase winding is compared with the demagnetization fault threshold to determine whether the motor is in a demagnetization fault state. If the motor is not in a demagnetization fault state, the motor operates normally. If the motor is in a demagnetization fault state, demagnetization protection is performed.

[0029] like Figure 1 As shown, a motor control anti-demagnetization protection method comprises the following steps:

[0030] Step 1: Obtain the back EMF parameter e0 measured on the motor test bench corresponding to the current speed.

[0031] Specifically, the method for implementing step 1 is:

[0032] The motor winding back EMF e0 under fault-free conditions is obtained by calibration.

[0033] The specific calibration method is: use the bench to measure the winding back electromotive force e0 at different speeds of the motor without demagnetization fault. The bench drags the motor to rotate, and the step length is set to 1000rpm, so that the motor speed increases from low to high until the peak speed. At each speed, the oscilloscope probe and ground wire connector are connected to the two phases of the motor respectively, the motor is rotated, the back electromotive force waveform is measured, the data is recorded, and the measured data is made into a one-dimensional table with the horizontal axis as the speed and the vertical axis as the back electromotive force.

[0034] Step 2: Obtain the rotor electrical angular frequency fe and the back electromotive force coefficient f of the coil in the stator slot D , slot angle θ. The slot angle θ represents the electrical angle difference between two adjacent stator slots, and the slot angle θ is directly obtained by the motor manufacturer.

[0035] Specifically, the method for implementing step 2 is:

[0036] The specific calculation formula for obtaining the rotor electrical angular frequency fe is: Where n is the speed, P is the number of pole pairs, which can be 3 or 4, depending on the specific design of the motor, and Pi is the pi;

[0037] By accurately calculating the electrical angular frequency, the motor speed can be precisely controlled. In a motor drive system, the controller can adjust the electrical angular frequency according to the required speed to ensure that the motor runs at the desired speed.

[0038] Understanding the electrical angular frequency of a motor helps optimize its performance. For example, in a variable frequency speed control system, the motor speed can be changed by adjusting the electrical angular frequency, thereby adjusting the motor output power and efficiency to meet different working requirements.

[0039] Abnormal changes in electrical angular frequency may be an indication of motor failure. By monitoring the electrical angular frequency, abnormal conditions in motor operation, such as speed fluctuations, load changes, etc., can be discovered in a timely manner, thereby performing fault diagnosis and early warning.

[0040] The formula for calculating the back electromotive force coefficient fD of the coil in the stator slot is: in Vpp is the peak-to-peak value of the back EMF waveform at each speed.

[0041] Back EMF coefficient f D It is an important parameter for evaluating motor performance. It reflects the magnitude of the back electromotive force generated by the stator coil at a specific speed. By calculating f D , we can understand the electromagnetic performance of the motor under different working conditions, and provide a basis for the design, optimization and fault diagnosis of the motor.

[0042] During the operation of the motor, if f D Abnormal changes in the value may mean that the motor has some kind of fault or performance degradation. For example, a decrease in back EMF may indicate that the motor winding has a short circuit or open circuit. D By monitoring the change in the value, potential faults of the motor can be discovered in time, and corresponding maintenance measures can be taken to avoid the expansion of the fault.

[0043] And in the motor control system, understanding the back EMF characteristics of the motor helps to optimize the control strategy. For example, in vector control or direct torque control, by accurately calculating the back EMF coefficient, the motor torque and speed can be precisely controlled, improving the dynamic response performance and stability of the system.

[0044] The energy efficiency of the motor can be improved by optimizing the back EMF characteristics of the motor. For example, by properly selecting parameters such as the number of pole pairs and the number of slots in the motor design, the motor can have higher efficiency and lower losses under specific operating conditions. In addition, during the operation of the motor, the energy efficiency can also be improved by adjusting the control strategy to match the back EMF characteristics of the motor.

[0045] Step 3: Calculate the winding back EMF e at time t An (t).

[0046] Specifically, the method for implementing step 3 is:

[0047] Step 3: The winding back electromotive force at time t is e An (t) specifically refers to the real-time back EMF of each coil in each phase winding of the motor. According to the designed motor coil winding, each coil has two adjacent slots, one of which is the incoming line and the other is the outgoing line.

[0048] The specific method for calculating the real-time back electromotive force of each coil in each phase winding of the motor is as follows: first, according to the rotor electrical angular frequency fe, the back electromotive force coefficient f of the coil in the stator slot D , slot angle θ to calculate the real-time back EMF of the coil in the incoming stator slot and the real-time back EMF of the coil in the outgoing stator slot of each coil, and then calculate the real-time back EMF of each coil in each phase winding of the motor based on the real-time back EMF of the coil in the incoming stator slot and the real-time back EMF of the coil in the outgoing stator slot of each coil

[0049] Taking the three coils of phase a winding as an example, the calculation formula is as follows:

[0050] The back electromotive force of the first coil of the a-phase winding entering the stator slot at time t is: e1(t)=cos(2πf e t)*f D ;

[0051] The back electromotive force of the coil in the stator slot of the first coil of the a-phase winding at time t is: e2(t)=cos(2πf e t-θ)*f D ;

[0052] The back electromotive force of the second coil of the a-phase winding entering the stator slot at time t is: e3(t) = cos(2πf e t)*f D ;

[0053] The back electromotive force of the second coil of the a-phase winding in the stator slot at time t is: e4(t)=cos(2πf e t-θ)*f D ;

[0054] At time t, the back electromotive force of the third coil of the a-phase winding entering the stator slot is: e5(t)=cos(2πf e t)*f D ;

[0055] The back electromotive force of the third coil of the a-phase winding in the stator slot at time t is: e6(t)=cos(2πf e t-θ)*f D ;

[0056] The real-time back EMF of each coil in each winding of the motor is obtained by subtracting the real-time back EMF of the coil in the incoming stator slot from the real-time back EMF of the coil in the outgoing stator slot.

[0057] Taking the three coils of phase a winding as an example, the calculation formula is as follows:

[0058] Back EMF of the first coil of phase a winding at time t: e A1 (t) = e1(t) – e2(t);

[0059] The back electromotive force of the second coil of phase a at time t: e A2 (t) = e3(t) – e4(t);

[0060] The back electromotive force of the third coil of phase a winding at time t: e A3 (t) = e5(t) – e6(t);

[0061] Similarly, the back electromotive force of the three coils of the b-phase winding and the c-phase winding at time t can be calculated.

[0062] The back EMF of the motor is the electromotive force in the opposite direction of the external force generated by the motor or generator based on the principle of electromagnetic induction when it is driven by voltage, current, etc. The existence of the back EMF will reduce the actual working voltage of the motor. Since the back EMF is opposite to the external voltage, it will offset part of the externally applied voltage, resulting in a reduction in the actual voltage obtained by the motor. This will in turn affect the speed and output power of the motor, and affect the performance of the motor. When the motor is running, the existence of the back EMF will change the electromagnetic field of the motor. If the back EMF is not processed, it may cause the magnetic flux of the motor to fluctuate, causing vibration and noise of the motor, and then affect the overall structure of the motor, and have an adverse effect on the operating stability and life of the motor. The existence of the back EMF will also affect the control accuracy of the motor. When the motor controller tries to control the speed or torque of the motor, the back EMF will interfere with it. This interference will cause the actual operating speed or torque of the motor to have an error with the expected value, thereby affecting the control accuracy and response speed of the motor. Therefore, by monitoring and controlling the back EMF of the motor, the purpose of improving the control accuracy of the motor and strengthening the fault protection of the motor can be achieved.

[0063] Step 4: Calculate the back EMF e of the three-phase winding of the motor at time t a (t), e b (t), e c (t).

[0064] Step 4: The back electromotive force e of the three-phase winding of the motor a (t), e b (t), e c (t), are the real-time back EMF of phase a winding, the real-time back EMF of phase b winding, and the real-time back EMF of phase c winding. In order to calculate the real-time back EMF of each coil in each phase winding of the motor, it is necessary to add the back EMFs of all coils in each phase winding to obtain the real-time back EMF of each phase winding of the motor.

[0065] The specific calculation formula is as follows:

[0066] e a (t) = e A1 (t)+e A2 (t)+e A3 (t):

[0067] e b (t) = e B1 (t)+e B2 (t)+e B3 (t);

[0068] e C (t) = e C1 (t)+e C2 (t)+e C3 (t);

[0069] Among them, e a (t) is the real-time back EMF of phase a winding, e A1 (t) is the back EMF of the first coil of phase a winding at time t, e A2 (t) is the back EMF of the second coil of phase a at time t, e A3 (t) is the back EMF of the third coil of phase a winding at time t; e b (t) is the real-time back EMF of phase b winding, e B1 (t) is the back EMF of the first coil of phase b at time t, e B2 (t) is the back EMF of the second coil of phase b at time t, e B3 (t) is the back EMF of the third coil of phase b at time t; e C (t) is the real-time back EMF of the c-phase winding, e C1 (t) is the back EMF of the first coil of the c-phase winding at time t, e C2 (t) is the back EMF of the second coil of the c-phase winding at time t, e C3 (t) is the back EMF of the third coil of the c-phase winding at time t.

[0070] Step 5: Use the measured back EMF e obtained by looking up the table at the current speed a (t), e b (t), e c (t) and obtain Δea(t), Δeb(t), Δe c (t).

[0071] Specifically, the method for implementing step 5 is:

[0072] The measured back EMF obtained by looking up the table at the current speed in step 5 is the back EMF of the winding under the fault-free condition corresponding to the current speed. The calculated real-time back EMF of the three-phase winding is subtracted from the back EMF e0 of the winding under the fault-free condition corresponding to the current speed: Δea(t)=e0-e a (t);

[0073] Δeb(t)=e0-e b (t);

[0074] Δe c (t) = e0 - e c (t);

[0075] Step 6: Calculate |Δea(t)|, |Δeb(t)|, |Δe c (t)|, the maximum value Δe(t)Max among the back electromotive forces of the three-phase windings.

[0076] Specifically, the method to implement Step 6 is as follows:

[0077] Δe(t)Max = max(|Δea(t)|, |Δeb(t)|, |Δe c (t)|);

[0078] When faults such as short circuit, open circuit, or demagnetization occur in the motor windings, its back electromotive force will deviate from the normal value, resulting in an increase in the calculated difference. Therefore, calculating the maximum difference of the real-time back electromotive force of the motor windings can detect and locate faults in a timely manner, thereby avoiding the expansion of faults or causing more serious consequences. And by subtracting the real-time back electromotive force of each phase winding in the three-phase windings from the back electromotive force of the winding under fault-free conditions respectively, the sensitivity of the motor to demagnetization faults is improved and it can be monitored in real time whether the motor is in a demagnetization fault.

[0079] Step 7: Compare Δe(t)Max with the demagnetization fault threshold to determine whether Δe(t)Max is greater than the demagnetization fault threshold.

[0080] Specifically, the method to implement Step 7 is as follows:

[0081] Judge the magnitude of the maximum difference Δe(t)Max of the real-time back electromotive force of the motor windings and the demagnetization fault threshold a. When Δe(t)Max < a, the motor controller normally executes the current torque command, otherwise, linear derating processing is performed.

[0082] The specific method for the motor controller to perform derating processing is: perform linear derating processing by outputting a derated torque Ft is the torque currently being executed. After derating processing, the derated torque F is obtained. While performing linear derating processing, a motor demagnetization fault code is issued to transmit the fault information to the whole vehicle and request a stop for inspection.

[0083] Embodiment 2

[0084] As Figure 2 shown, the motor control anti-demagnetization protection system applying the above-mentioned motor control anti-demagnetization protection method includes a back electromotive force acquisition module and an anti-demagnetization protection module;

[0085] The back electromotive force acquisition module is used to acquire the back electromotive force of the motor windings under fault-free conditions and the real-time back electromotive force of each phase winding of the motor;

[0086] The anti-demagnetization protection module is used to make a difference between the back EMF of the motor winding under fault-free conditions and the real-time back EMF of each phase winding of the motor, and obtain the maximum difference of the real-time back EMF of the motor phase winding;

[0087] The anti-demagnetization protection module is also used to compare the maximum difference in real-time back electromotive force of the motor phase winding with the demagnetization fault threshold to determine whether the motor is in a demagnetization fault state. When the motor is not in a demagnetization fault state, the motor runs normally. When the motor is in a demagnetization fault state, demagnetization protection is performed.

[0088] Example 3

[0089] The present invention also includes a computer program product, including a computer program / instruction, which implements the steps of the above-mentioned motor control anti-demagnetization protection method when executed by a processor.

Claims

1. A motor control anti-demagnetization protection method, characterized in that: It includes: Obtain the back EMF of the motor winding under fault-free conditions and the real-time back EMF of each phase winding of the motor; The back EMF of the motor winding under fault-free conditions is subtracted from the real-time back EMF of each phase winding of the motor to obtain the maximum difference of the real-time back EMF of the motor phase winding; The maximum real-time back-electromotive force difference of the motor phase winding is compared with the demagnetization fault threshold to determine whether the motor is in a demagnetization fault state. If the motor is not in a demagnetization fault state, the motor operates normally. If the motor is in a demagnetization fault state, demagnetization protection is performed.

2. A motor control anti-demagnetization protection method according to claim 1, characterized in that: The motor winding back EMF under fault-free conditions is obtained by calibration.

3. The motor control anti-demagnetization protection method according to claim 1, characterized in that: The method for obtaining the real-time back electromotive force of each phase winding of the motor includes: calculating the real-time back electromotive force of each coil in each phase winding of the motor, and adding the back electromotive force of all coils in each phase winding to obtain the real-time back electromotive force of each phase winding of the motor.

4. A motor control anti-demagnetization protection method according to claim 3, characterized in that: The method for calculating the real-time back EMF of each coil in each phase winding of a motor includes: calculating the real-time back EMF of the coil in the incoming stator slot and the real-time back EMF of the coil in the outgoing stator slot of each coil, and obtaining the real-time back EMF of each coil in each phase winding of the motor by subtracting the real-time back EMF of the coil in the incoming stator slot from the real-time back EMF of the coil in the outgoing stator slot.

5. A motor control anti-demagnetization protection method according to claim 4, characterized in that: The method for calculating the real-time back electromotive force of the coil in the incoming stator slot and the real-time back electromotive force of the coil in the outgoing stator slot of each coil includes: the real-time back electromotive force of the coil in the incoming stator slot and the real-time back electromotive force of the coil in the outgoing stator slot of each coil are calculated based on the electrical angular frequency of the rotor operation, the back electromotive force coefficient of the coil in the stator slot and the slot angle of the motor.

6. A motor control anti-demagnetization protection method according to claim 5, characterized in that: The method for obtaining the electrical angular frequency of the rotor and the back electromotive force coefficient of the coil in the stator slot includes: obtaining the electrical angular frequency of the rotor and the back electromotive force coefficient of the coil in the stator slot according to the real-time speed of the motor.

7. A motor control anti-demagnetization protection method according to claim 1, characterized in that: The method for obtaining the maximum difference in real-time back-EMF of motor phase windings includes: subtracting the real-time back-EMF of each phase winding of the motor from the back-EMF of the winding under fault-free conditions corresponding to the current speed to obtain a set of differences, and taking the maximum value in the set of differences as the maximum difference in real-time back-EMF of the motor phase windings.

8. The motor control anti-demagnetization protection method according to claim 1, characterized in that: The method for performing demagnetization protection according to the maximum difference of the real-time back-electromotive force of the motor phase winding includes: judging the size of the maximum difference of the real-time back-electromotive force of the motor phase winding and the demagnetization fault threshold; when the maximum difference of the real-time back-electromotive force of the motor phase winding is less than the demagnetization fault threshold, the motor controller executes the current torque command normally, otherwise linear derating is performed.

9. A motor control anti-demagnetization protection system, characterized in that: It includes a back-EMF acquisition module and an anti-demagnetization protection module; The back-EMF acquisition module is used to obtain the back-EMF of the motor winding under fault-free conditions and the real-time back-EMF of each phase winding of the motor; The anti-demagnetization protection module is used to make a difference between the back EMF of the motor winding under fault-free conditions and the real-time back EMF of each phase winding of the motor, and obtain the maximum difference of the real-time back EMF of the motor phase winding; The anti-demagnetization protection module is also used to compare the maximum difference in real-time back electromotive force of the motor phase winding with the demagnetization fault threshold to determine whether the motor is in a demagnetization fault state. When the motor is not in a demagnetization fault state, the motor runs normally. When the motor is in a demagnetization fault state, demagnetization protection is performed.

10. A computer program product, comprising a computer program / instruction, which implements the steps of the method as claimed in claim 1 when executed by a processor.

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