Dual three-phase permanent magnet motor torque ripple suppression fault-tolerant control method based on harmonic current injection

Abstract

The invention discloses a dual three-phase permanent magnet motor torque ripple suppression fault-tolerant control method based on harmonic current injection. The implementation of the method mainly comprises the following steps: analyzing the composition of main torque pulsation after a motor fault, and measuring the back electromotive force harmonic content of the main torque pulsation; torque pulsation generated by each order of counter electromotive force harmonic wave is deduced by using the measured data; and determining a harmonic current reference coefficient during fault-tolerant operation according to a required fault-tolerant effect, and calculating a harmonic component of the injected q-axis current by using known information. Harmonic waves are injected into q-axis current reference, so that the part of harmonic wave current acts with counter potential fundamental waves to generate a part of active torque ripples to counteract passive torque ripples generated by interaction of the counter potential harmonic waves and the current fundamental waves; therefore, the overall torque ripple during fault-tolerant operation of the motor can be well reduced.

Description

Technical Field

[0001] The present invention belongs to the field of multi-phase motor control, and in particular relates to a method for suppressing torque pulsation of a dual three-phase permanent magnet motor in a fault-tolerant operating state. Background Art

[0002] The demand for high reliability, high performance, and high power density in fields such as ship propulsion and aerospace has led to the increasing application of multiphase permanent magnet motors. However, since motors are subject to inevitable failures during operation, stable operation under fault conditions is particularly important. Fault-tolerant control of permanent magnet motors can be divided into two categories: one based on the motor's design, which is typically achieved through redundant design and other methods, resulting in high costs; the other based on the control algorithm, which does not require changes to the motor structure and is relatively low-cost. Control methods based on the normal decoupling transformation matrix have become a hot topic of research due to their high performance, simple implementation, and wide applicability. However, the traditional isolated neutral point connection of dual three-phase permanent magnet motors limits their fault-tolerant operation capabilities. In contrast, a single neutral point connection can achieve lower copper losses or superior torque output. However, when an open-circuit fault occurs in a single neutral point connection, the coupling between the fundamental and harmonic spaces causes the back EMF harmonics to interact with the current, generating large torque ripples that affect the motor's operational stability. Summary of the Invention

[0003] Purpose of the invention: In order to address the problem that when an open circuit fault occurs in a dual three-phase permanent magnet motor with a single neutral point connection, the coupling of the fundamental space and the harmonic space will cause the interaction between the back electromotive force harmonics and the current to produce large torque pulsations. The present invention provides a torque pulsation suppression fault-tolerant control strategy. By injecting harmonics into the q-axis current reference, this part of the harmonic current interacts with the back electromotive force fundamental to generate a part of active torque pulsations to offset the passive torque pulsations generated by the interaction between the back electromotive force harmonics and the current fundamental, thereby reducing the overall torque pulsations of the motor, while achieving the optimization of the fault-tolerant target and the suppression of torque pulsations, improving the performance of the motor during fault-tolerant operation, and enhancing stability and reliability.

[0004] The technical solution is: a fault-tolerant control method for torque ripple suppression of a dual three-phase permanent magnet motor, characterized by comprising the following steps:

[0005] Step 1: Analyze the composition of the main torque ripple of the dual three-phase permanent magnet motor after the fault, and use FFT to measure the back EMF harmonic content of the motor.

[0006] Step 2: Using the data measured in step 1, derive the torque ripple generated by each order of back EMF harmonics.

[0007] Step 3: Determine the coefficient of the harmonic current reference during fault-tolerant operation based on the required fault-tolerant effect, and calculate the harmonic component of the injected q-axis current using the known information.

[0008] Step 4: The voltage reference in the rotating coordinate system of dqxyo1o2 is transformed into the voltage reference in the original stationary coordinate system of abcdef through coordinate transformation. The PWM signal required by the inverter is generated by SPWM, and the inverter is connected to the motor for control.

[0009] Furthermore, the dual three-phase permanent magnet motor torque pulsation suppression fault-tolerant control strategy is characterized by: analyzing the composition of the main torque pulsation after the dual three-phase permanent magnet motor fails, including the secondary torque pulsation generated by the interaction between the back electromotive force fundamental wave and the current fundamental wave directly caused by the motor failure. This part of the torque pulsation is always zero when the motor is in fault-tolerant operation.

[0010] In addition, it also includes the torque pulsation caused by the interaction between the back-electromotive force harmonics of each order and the current fundamental wave due to the coupling of the fundamental wave space and the harmonic space after the fault. This part of the torque pulsation is the main torque pulsation during the fault-tolerant operation of the motor.

[0011] The back EMF of the dual three-phase permanent magnet motor is measured, and the FFT analysis of the back EMF waveform is performed to obtain the harmonic content of each order.

[0012] Furthermore, the fault-tolerant control strategy for torque ripple suppression of dual three-phase permanent magnet motors is characterized by: based on the fact that torque can be expressed as the partial derivative of magnetic field energy storage with respect to mechanical angular displacement, the torque DC component generated by the back-EMF fundamental wave and the torque ripple components generated by each order of back-EMF harmonics are derived. This is shown in the following formula:

[0013]

[0014] It should be noted that since the back electromotive force is the product of the differential term of the permanent magnet magnetic flux and the electrical angular velocity, the permanent magnet magnetic flux can be used to represent the effect of the back electromotive force.

[0015] Furthermore, the dual three-phase permanent magnet motor torque ripple suppression fault-tolerant control strategy is characterized in that the coefficient of the harmonic current reference during fault-tolerant operation is determined according to the required fault-tolerant effect. Assuming that the motor fault is an open circuit of phase F, the constraints satisfied by the harmonic current reference are shown in the following formula:

[0016]

[0017] It should be noted that the harmonic current references herein are all expressed as linear combinations of fundamental current references, that is, the harmonic current references can be expressed using q-axis current references through rotating coordinate transformation.

[0018] If the minimum copper loss during motor operation is selected as the fault tolerance target, the harmonic current reference is as follows:

[0019]

[0020] The harmonic components of the injected q-axis current are calculated. The final q-axis current reference after injection is shown in the following formula:

[0021]

[0022] The active torque pulsation generated by the interaction between the injected harmonic current component and the back-EMF fundamental component will offset the passive torque pulsation generated by the interaction between the back-EMF harmonic component and the current fundamental component, thereby significantly reducing the overall torque pulsation, making the motor operation smoother and more stable, and increasing the reliability of the motor during fault-tolerant operation.

[0023] Furthermore, the fault-tolerant control strategy for torque ripple suppression of dual three-phase permanent magnet motors is characterized by transforming the voltage reference in the rotating coordinate system dqxyo1o2 into the voltage reference in the original stationary coordinate system abcdef, utilizing SPWM modulation technology to generate the PWM signal required by the inverter, and connecting the inverter to the motor for control. The coordinate transformation process is shown in the following equation:

[0024]

[0025]

[0026] [f A f B f C f D f E f F ] T =T αβ -1 T dq -1 [f d f q f x f y f o1 f o2 ] T (20)

[0027] Technical effects: The beneficial effects of the present invention are:

[0028] 1. The present invention effectively suppresses torque ripple during fault-tolerant operation of a dual three-phase permanent magnet motor after an open-circuit fault by injecting harmonic components into the q-axis current.

[0029] 2. The present invention is applicable to any control strategy that achieves fault-tolerant operation by modifying the harmonic current reference. It is applicable not only to single-phase open circuit faults but also to two-phase open circuit faults, and has a wide range of applicability.

[0030] 3. The present invention achieves both optimization of fault tolerance targets and effective suppression of torque pulsation in the fault-tolerant operation state of a dual three-phase permanent magnet motor, and can effectively suppress torque pulsation when the motor operates with minimum copper loss or other fault-tolerant targets.

[0031] 4. The present invention injects harmonics into the q-axis current reference, allowing these harmonic currents to interact with the back-EMF fundamental wave, generating a portion of active torque ripple to offset the passive torque ripple generated by the interaction between the back-EMF harmonics and the current fundamental wave. This significantly reduces the overall torque ripple during fault-tolerant operation of the motor. This invention is applicable not only to single-phase open-circuit faults but also to two-phase open-circuit faults. Furthermore, it is particularly effective for motors with high harmonic flux content. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 A system block diagram of a fault-tolerant control strategy for torque ripple suppression of a dual three-phase permanent magnet motor provided by an embodiment of the present invention

[0033] Figure 2 The motor back EMF waveform provided by the embodiment of the present invention

[0034] Figure 3 FFT analysis diagram of the motor back EMF provided by the embodiment of the present invention

[0035] Figure 4 Winding configuration of a dual three-phase permanent magnet motor provided by an embodiment of the present invention

[0036] Figure 5 The simulation results of torque under the traditional minimum copper loss fault tolerance strategy provided by the embodiment of the present invention are as follows:

[0037] Figure 6 The simulation results of the torque generated by the back EMF fundamental wave and the torque generated by the back EMF harmonics after the harmonic injection provided by the embodiment of the present invention are offset by each other.

[0038] Figure 7 The simulation results of torque under the minimum copper loss fault tolerance strategy after harmonic injection provided by the embodiment of the present invention are as follows DETAILED DESCRIPTION

[0039] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0040] like Figure 1 As shown in the figure, it is a structural block diagram of a fault-tolerant control system for torque pulsation suppression of a dual three-phase permanent magnet motor based on harmonic current injection, which mainly includes a PI control module, a coordinate transformation module, a PWM modulation module, an inverter and motor module, a fault-tolerant current reference calculation module, and an injected q-axis current calculation module.

[0041] Firstly, the composition of the main torque pulsation after the dual three-phase permanent magnet motor fault is analyzed, including the secondary torque pulsation caused by the interaction between the back electromotive force fundamental wave and the current fundamental wave directly caused by the motor fault. This part of the torque pulsation is always zero when the motor is in fault-tolerant operation.

[0042] In addition, it also includes the torque pulsation caused by the interaction between the back-electromotive force harmonics of each order and the current fundamental wave due to the coupling of the fundamental wave space and the harmonic space after the fault. This part of the torque pulsation is the main torque pulsation during the fault-tolerant operation of the motor.

[0043] Secondly, the back EMF of the dual three-phase permanent magnet motor is measured. The measured back EMF waveform is as follows: Figure 2 The back EMF waveform is analyzed by FFT to obtain the harmonic content of each order. The analyzed back EMF spectrum is shown as follows: Figure 3 As shown in the figure, it can be seen that the back EMF harmonics of the prototype used are mainly 3rd order, with a content as high as 27.3%, while the 5th and 7th order harmonics are relatively low, both less than 2%. In order to make the motor have better fault tolerance after a fault, the prototype winding is configured as a non-isolated neutral point connection method, that is, a single neutral point connection method, as shown in the figure. Figure 4 shown.

[0044] Since torque can be expressed as the partial derivative of magnetic field energy storage with respect to mechanical angular displacement, the torque DC component generated by the back-EMF fundamental wave and the torque ripple components generated by each order of back-EMF harmonics are derived. This is shown in the following formula:

[0045]

[0046] It should be noted that since the back electromotive force is the product of the differential term of the permanent magnet magnetic flux and the electrical angular velocity, the permanent magnet magnetic flux can be used to represent the effect of the back electromotive force.

[0047] The coefficient of the harmonic current reference during fault-tolerant operation is determined based on the required fault-tolerant effect. Assuming that the motor fault is an open circuit of phase F, the constraints satisfied by the harmonic current reference are shown in the following equation:

[0048]

[0049] It should be noted that the harmonic current references herein are all expressed as linear combinations of fundamental current references, that is, the harmonic current references can be expressed using q-axis current references through rotating coordinate transformation.

[0050] If the minimum copper loss during motor operation is selected as the fault tolerance target, the harmonic current reference is as follows:

[0051]

[0052] The torque under the traditional minimum copper loss fault tolerance strategy includes the DC amount generated by the interaction between the back EMF fundamental wave and the current, as well as the pulsation amount generated by the interaction between the back EMF harmonics and the current. Therefore, the overall torque pulsation is large, at 5.41%. The simulation results are as follows: Figure 5 shown.

[0053] The harmonic components of the injected q-axis current are calculated. The final q-axis current reference after injection is shown in the following formula:

[0054]

[0055] The active torque ripple generated by the interaction between the injected harmonic current component and the back-EMF fundamental component will offset the passive torque ripple generated by the interaction between the back-EMF harmonic component and the current fundamental component, thereby significantly reducing the overall torque ripple, making the motor run smoother and more stable, and increasing the reliability of the motor during fault-tolerant operation. The offset effect is as follows: Figure 6 As shown, where T e1 It represents the torque component generated by the fundamental wave of the back EMF. It can be seen that after the harmonics are injected, it changes from a DC quantity to a pulsating quantity. T e3 +T e5 +T e7 It represents the torque component generated by the back EMF harmonics. In order to better show the offset effect, a DC bias of 100 is added to it. The simulation results of the torque under the minimum copper loss fault tolerance strategy after harmonic injection are shown as follows: Figure 7 As shown in Figure 2, the torque ripple is reduced from 5.41% under the traditional minimum copper loss fault tolerance strategy to 1.04%.

[0056] The voltage reference in the rotating coordinate system dqxyo1o2 is transformed into the voltage reference in the original stationary coordinate system abcdef. The SPWM modulation technology is used to generate the PWM signal required by the inverter. The inverter is connected to the motor for control. The coordinate transformation process is shown in the following formula:

[0057]

[0058] [f A f B f C f D f E f F ] T =T αβ -1 Tdq -1 [f d f q f x f y f o1 f o2 ] T (30)

[0059] Throughout this specification, reference to terms such as "one embodiment," "some embodiments," "illustrative embodiments," "examples," "specific examples," or "some examples" means that a specific feature, structure, material, or characteristic described in conjunction with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, illustrative uses of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0060] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to the embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the claims and their equivalents.

Claims

1. A fault-tolerant control method for torque ripple suppression of dual three-phase permanent magnet motors based on harmonic current injection, characterized in that: It includes the following steps: Step 1: Analyze the composition of the main torque ripple of the dual three-phase permanent magnet motor after a fault, and use fast Fourier transform analysis (FFT) to measure the back EMF harmonic content of the motor; Step 2: Using the data measured in step 1, derive the torque ripple generated by each order of back EMF harmonics; Step 3: Determine the harmonic current reference coefficient during fault-tolerant operation based on the required fault-tolerant effect, and calculate the harmonic component of the injected q-axis current using the known information; Step 4: The voltage reference in the rotating coordinate system dqxyo1o2 is transformed into the voltage reference in the original stationary coordinate system abcdef through coordinate transformation. Sinusoidal pulse width modulation (SPWM) is used to generate the PWM signal required by the inverter. The inverter is connected to the motor for control.

2. The method according to claim 1, wherein: The composition of the main torque ripple after a dual three-phase permanent magnet motor fault is analyzed, including the secondary torque ripple caused by the interaction between the back EMF fundamental wave and the current fundamental wave directly caused by the motor fault. This part of the torque ripple is always zero during fault-tolerant operation of the motor. In addition, it also includes the torque ripple caused by the interaction between the back EMF harmonics of each order and the current fundamental wave due to the coupling between the fundamental wave space and the harmonic wave space after the fault. This part of the torque ripple is the main torque ripple during the fault-tolerant operation of the motor. The back EMF of the dual three-phase permanent magnet motor is measured, and the FFT analysis of the back EMF waveform is performed to obtain the harmonic content of each order.

3. The method according to claim 1, wherein: In step 2, based on the fact that torque can be expressed as the partial derivative of magnetic field energy storage with respect to mechanical angular displacement, the torque DC component generated by the back-EMF fundamental wave and the torque ripple components generated by each order of back-EMF harmonics are derived; As shown in the following formula: Where, T e1 is the DC component of the torque generated by the interaction between the back EMF fundamental wave and the current, T e3 、T e5 、T e7 are the torque ripple components generated by the interaction between the 3rd, 5th, and 7th back EMF harmonics and the current, respectively. n , I s ,θ e are the number of pole pairs, phase current and rotor position angle respectively, i x 、i y 、i o1 、i o2 is the actual value of the harmonic subspace current, ψ m1 , ψ m3 , ψ m5 , ψ m7 are the fundamental wave component and the 3rd, 5th and 7th harmonic components of the permanent magnet flux, respectively. q is the actual value of the q-axis current; it should be noted that since the back EMF is the product of the differential term of the permanent magnet magnetic flux and the electric angular velocity, the permanent magnet magnetic flux can be used to represent the effect of the back EMF.

4. The method according to claim 1, wherein: The coefficient of the harmonic current reference during fault-tolerant operation is determined based on the required fault-tolerant effect. Assuming that the motor fault is an open circuit of phase F, the constraints satisfied by the harmonic current reference are shown in the following equation: Where i *α 、i *β is the reference value of the fundamental subspace current, is the reference value of the harmonic subspace current, k1, k2, k3, and k4 are the coefficients of the harmonic current reference that meet the requirements of fault-tolerant operation. It should be noted that the harmonic current references here are all expressed as linear combinations of the fundamental current references, that is, the harmonic current references can be expressed as q-axis current references through rotating coordinate transformation. If the minimum copper loss during motor operation is selected as the fault tolerance target, the harmonic current reference is as follows: The harmonic components of the injected q-axis current are calculated. The final q-axis current reference after injection is shown in the following formula: In the formula, the last three terms on the right side of the equal sign are all functions of the first term; i q_ref is the reference value of the q-axis current after harmonic injection. The symbols on the right side of the equal sign mean: T e3 、T e5 、T e7 They are the torque ripple components generated by the interaction between the 3rd, 5th, and 7th back-EMF harmonics and the current, where * represents the reference value; The active torque pulsation generated by the interaction between the injected harmonic current component and the back-EMF fundamental component will offset the passive torque pulsation generated by the interaction between the back-EMF harmonic component and the current fundamental component, thereby significantly reducing the overall torque pulsation, making the motor operation smoother and more stable, and increasing the reliability of the motor during fault-tolerant operation.

5. The method according to claim 1, wherein: The voltage reference in the rotating coordinate system dqxyo1o2 is transformed into the voltage reference in the original stationary coordinate system abcdef through coordinate transformation. The SPWM modulation technology is used to generate the PWM signal required by the inverter. The inverter is connected to the motor for control. The coordinate transformation process is shown in the following formula: [f A f B f C f D f E f F ] T =T αβ -1 T dq -1 [f d f q f x f y f o1 f o2 ] T (10) Where, T αβ is the coordinate transformation matrix based on vector space decoupling transformation, T dq is the rotation coordinate transformation matrix, f A 、f B 、f C 、f D 、f E 、f F represents the variables in the original stationary coordinate system, f d 、f q 、f x 、f y 、f o1 、f o2 Represents a variable in a rotated coordinate system.

Images