Sensorless control method for dual three-phase permanent magnet synchronous motor robust to open-circuit fault

Abstract

The invention provides a dual three-phase permanent magnet synchronous motor sensorless control method robust to an open-circuit fault, and belongs to the technical field of dual three-phase permanent magnet synchronous motor sensorless control. The sliding-mode observer is designed according to the double d-q models of the double three-phase permanent magnet synchronous motor, and the influence of the coupling problem is eliminated; when the motor operates healthily, any three-phase winding is adopted to estimate the position of the rotor, and the other three-phase winding is used as a backup; when a single-phase open-circuit fault occurs, which set of three-phase winding the open-circuit fault occurs is diagnosed, according to a judgment result, another set of healthy three-phase winding is adopted to observe back electromotive force to extract rotor position information, and meanwhile, the coupling relation between the two sets of windings is considered to further improve the position observation precision. According to the invention, a position-sensorless control strategy is adopted, the reliability of the system is improved, and under the condition of a single-phase open-circuit fault, the system can still be normally used even if a fault-tolerant strategy is not adopted, so that the system has extremely high application value and economic value.

Description

Technical Field

[0001] The present invention relates to a sensorless control method for a dual three-phase permanent magnet synchronous motor that is robust to open-circuit faults, and belongs to the technical field of sensorless control of dual three-phase permanent magnet synchronous motors. Background Art

[0002] Dual three-phase permanent magnet synchronous motors (DTP-PMSMs) have been widely used in fields such as electric vehicles, more electric aircraft, and electric rail transit due to their high reliability, low torque ripple, and strong fault tolerance capabilities. To achieve their high-precision and fast-response control characteristics, accurate rotor position measurement is required, which is usually accomplished by position sensors. However, the reliability of position sensors is difficult to meet under extreme operating conditions, so sensorless control is crucial for high-precision and high-reliability control of motors.

[0003] The existing traditional sensorless control methods for three-phase permanent magnet synchronous motors are mainly divided into two categories: the first category is sensorless control based on the saliency effect of the motor, and the second category is sensorless control based on the mathematical model of the motor. The first category of methods mainly injects high-frequency signals into the motor and uses the response current generated by the saliency effect of the motor to extract the rotor position information, which is commonly used at low and zero speeds of the motor. The second category of methods mainly designs a state observer based on the motor model, observes the back electromotive force or magnetic flux of the motor, and then extracts the rotor position information from it, which is commonly used at medium and high speeds of the motor. Due to the structural similarity between the dual three-phase permanent magnet synchronous motor and the three-phase permanent magnet synchronous motor, only the number of stator phases is different. When performing sensorless control on the dual three-phase permanent magnet synchronous motor, the sensorless control algorithm of the three-phase permanent magnet synchronous motor can often be borrowed or even transplanted. In addition, the dual three-phase motor also has strong fault tolerance. Although the above methods can accurately estimate the rotor position information during the healthy operation of the motor, when a single-phase open-circuit fault (OPF) occurs in the motor, the estimated rotor position accuracy cannot reach the expected effect, resulting in the motor stopping running or even damaging the inverter. The literature "Fault-tolerant sensorless control for six-phase PMSM with dual back-EMF observer," M. Furmanik, G. Scelb a, and P. Rafajdus, in Proc. Int. Symp. Power Electron., Elect. Drives, Automat. Motion (SPEEDAM), Sorrento, Italy. Piscataway, NJ, USA: IEEE Press, Jun. 2022, pp. 305–311, proposed a sensorless control method based on dual back electromotive force, in which the rotor position information obtained from the observer is used for backup of sensor faults and experiments were carried out under OPF. However, the premise is that the sensor fault occurs after OPF occurs and the fault-tolerant algorithm is implemented, which is unacceptable in practical applications.The sensorless control method proposed in the literature "A modified flux observer for sensorless direct torque control of dual three-phase PMSM considering open-circuit fault," N. X. Qiu, J. Ji, D. Zhou, W. Zhao, Y. Chen, and L. Huang, IEEE Trans. Power Electron., vol. 37, no. 12, pp. 15356–15369, Dec. 2022, can obtain an acceptable rotor speed when an OPF occurs under direct torque control, but the rotor position estimation error is still large before implementing the fault-tolerant algorithm.

[0004] Therefore, the present invention proposes a novel sensorless control method for a dual three-phase permanent magnet synchronous motor based on a sliding mode observer (SMO) to accurately estimate the rotor position information under normal operation and open-circuit faults, and no additional fault-tolerant algorithm is required to maintain the accuracy of the position information. Summary of the Invention

[0005] The object of the present invention is to solve the problem that the existing sensorless control strategy needs to adopt a fault-tolerant strategy to be used normally under the condition of single-phase open-circuit fault, and further provide a sensorless control method for a dual three-phase permanent magnet synchronous motor that is robust to open-circuit faults.

[0006] Specifically, in the single-phase open-circuit fault of a surface-mounted permanent magnet synchronous motor, an SMO is designed based on the dual d-q coordinate transformation to observe the three healthy-phase windings in the two sets of windings to avoid the back electromotive force distortion observed in the case of open-circuit faults. And the present invention also takes into account the coupling between the two sets of three-phase windings and eliminates its influence by combining a mathematical model. The experimental results show that the method of the present invention can accurately estimate the rotor position under the open-circuit fault of a dual three-phase permanent magnet synchronous motor.

[0007] The object of the present invention is achieved by the following technical solutions:

[0008] A sensorless control method for a dual three-phase permanent magnet synchronous motor that is robust to open-circuit faults includes the following steps:

[0009] Step 1: Design a sliding mode observer and a phase-locked loop according to the dual d-q model of the dual three-phase permanent magnet synchronous motor. Considering the coupling between the two sets of three-phase windings of the motor, obtain the mathematical model of the coupling phase and decouple it to obtain the decoupled generalized α-β stationary coordinate system voltage, which is used as the voltage input of the sliding mode observer to eliminate the coupling effect;

[0010] Step 2: When the dual three-phase permanent magnet synchronous motor is operating healthily, use any one of the two sets of three-phase windings of the motor to apply the sliding mode observer designed in Step 1 to observe its back electromotive force, and extract the rotor position information through a phase-locked loop. The other set of three-phase windings serves as a backup.

[0011] Step 3: When a single-phase open circuit fault occurs in the dual three-phase permanent magnet synchronous motor, first determine in which set of the two sets of three-phase windings the open circuit fault of the dual three-phase permanent magnet synchronous motor occurs, and then adopt different back electromotive force observation strategies according to the judgment result.

[0012] When a single-phase open circuit fault occurs in one of the sets of three-phase windings, use the healthy other set of three-phase windings to observe the back electromotive force. The input quantities of the sliding mode observer are u″ αβ and i αβ of the healthy three-phase winding, where u" αβ is the generalized α, β-axis voltage of the healthy three-phase winding, and i αβ is the α, β-axis current of the healthy three-phase winding, and the rotor position information in the back electromotive force is extracted through a phase-locked loop.

[0013] Preferably, in Step 1, the phase difference between the corresponding phases of the two sets of three-phase windings is 30° electrical angle.

[0014] Preferably, in Step 3, the specific method for judging the open circuit fault of the dual three-phase permanent magnet synchronous motor is as follows: Use a four-dimensional vector controller to control the dual three-phase permanent magnet synchronous motor. The four-dimensional vector controller includes a speed closed loop and four current closed loops: d-axis, q-axis, x-axis, and y-axis; Use four current sensors to monitor the current data of the four current closed loops, and obtain the actual six-phase current of the dual three-phase permanent magnet synchronous motor through the current data returned by the four current sensors. If the average current of a certain phase remains 0 within half an electrical cycle, it means that there is an open circuit fault in this set of three-phase windings.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0016] Compared with the prior art where using a position sensor will increase costs and installation space, the present invention proposes a sensorless control strategy applicable to a dual three-phase permanent magnet synchronous motor. The structure is simple and easy to implement, which can improve the reliability of the system, enable the motor to operate reliably, and can still be used normally under the condition of a single-phase open circuit fault without adopting a fault tolerance strategy, having extremely high application value and economic value.

[0017] In the present invention, the error before and after the fault remains basically unchanged. According to the experimental results, the higher the motor speed, the better the performance of the method of the present invention when OPF_F occurs. Therefore, the rotor position estimation error during the open-circuit fault can be greatly reduced, and the system stability can be significantly improved.

[0018] The present invention proposes a sliding mode observer based on double d-q coordinate transformation for sensorless control of a dual three-phase permanent magnet synchronous motor under open-circuit faults. This method has the advantages of high precision and strong robustness. In addition, compared with other sensorless control methods under OPF, this method has lower requirements for the fault diagnosis algorithm, reduces the design difficulty of the fault diagnosis algorithm, and can ensure the accuracy of the estimated rotor position information without implementing an additional fault tolerance algorithm. Brief Description of the Drawings

[0019] Figure 1 It is the four-dimensional vector control block diagram of the dual three-phase motor of the present invention.

[0020] Figure 2 It is the topology diagram of the sensorless control method of the present invention.

[0021] Figure 3 It is the comparison experimental contrast diagram when OPF_F occurs under the rated load.

[0022] Among them, Figure 3 (a) is the electromotive force amplitude diagram observed in the α-β subspace using the traditional method at the rated load of 600 rpm;

[0023] Figure 3 (b) is the electromotive force amplitude diagram observed in the α-β subspace using the method of the present invention at the rated load of 600 rpm;

[0024] Figure 3 (c) is the rotor position and speed error diagram estimated using the traditional method at the rated load of 600 rpm;

[0025] Figure 3 (d) is the rotor position and speed error diagram estimated using the method of the present invention at the rated load of 600 rpm;

[0026] Figure 3 (e) is the electromotive force amplitude diagram observed in the α-β subspace using the traditional method at the rated load of 900 rpm;

[0027] Figure 3 (f) is the electromotive force amplitude diagram observed in the α-β subspace using the method of the present invention at the rated load of 900 rpm;

[0028] Figure 3(g) is the diagram of estimating rotor position and speed error using the traditional method at the rated load of 900 rpm;

[0029] Figure 3 (h) is the diagram of estimating rotor position and speed error using the method of the present invention at the rated load of 900 rpm.

[0030] Figure 4 It is the comparison diagram of the traditional method and the method of the present invention at 600 to 900 rpm under the rated load.

[0031] Among them, Figure 4 (a) is the diagram of rotor position and speed error under normal operation using the traditional method;

[0032] Figure 4 (b) is the diagram of rotor position and speed error under normal operation using the method of the present invention;

[0033] Figure 4 (c) is the diagram of rotor position and speed error under OPF_F using the method of the present invention. Detailed implementation manners

[0034] The present invention will be further described in detail below in conjunction with the accompanying drawings: This implementation manner is carried out on the premise of the technical solution of the present invention, and detailed implementation manners are given, but the protection scope of the present invention is not limited to the following implementation manners. Detailed implementation manner one:

[0036] As Figure 1 shown, the hardware part of the sensorless control system for a dual three-phase permanent magnet synchronous motor robust to open-circuit faults in this implementation manner mainly includes: a controller, a voltage source inverter (VSI), and a dual three-phase permanent magnet synchronous motor; in this implementation manner, the dual three-phase permanent magnet synchronous motor includes two sets of three-phase windings, the first set of three-phase windings (A, B, C) and the second set of three-phase windings (D, E, F), and the phase difference between the corresponding phases of the two sets of windings (such as phase A and phase D) is 30° electrical angle.

[0037] For the system software part, a four-dimensional vector controller is adopted to control the dual three-phase permanent magnet synchronous motor. The four-dimensional vector controller includes a speed closed-loop and four current closed-loops: d-axis, q-axis, x-axis, and y-axis. The position and phase current information of the dual three-phase permanent magnet synchronous motor are obtained through a sliding-mode observer + Phase-Locked Loop (PLL) and current sensors. The speed of the dual three-phase permanent magnet synchronous motor and the feedback values of the four current closed-loops of the d-axis, q-axis, x-axis, and y-axis are obtained through dual VSD coordinate transformation and corresponding operations. The current feedback value is subtracted from the reference value, and a Proportional Integral Controller (PI) is used for control. After the output result undergoes Space Vector Pulse Width Modulation (SVPWM), the control signal of the switching device is transmitted to the voltage source inverter to drive the dual three-phase permanent magnet synchronous motor to operate.

[0038] When a single-phase open-circuit fault (Open-phase Fault, OPF) occurs in the dual three-phase permanent magnet synchronous motor, since the inverter of the faulty phase is turned off, the voltage signal of the controller cannot be accurately transmitted to the motor terminal, resulting in an error between the output voltage of the controller of the open-circuit phase and the actual voltage of the winding, thus distorting the back electromotive force observed by the conventional sensorless method. Therefore, this embodiment provides a sensorless control method for a dual three-phase permanent magnet synchronous motor that is robust to open-circuit faults and can accurately estimate the rotor position under open-circuit fault conditions. This method designs a sliding-mode observer in the α-β subspace based on the dual d-q coordinate transformation model of the motor, and only uses the healthy three-phase windings to observe the back electromotive force, avoiding the distortion of the back electromotive force caused by the incorrect transmission of the voltage signal due to the open-circuit fault. In addition, the influence of the coupling between the two sets of windings on the control performance is also considered.

[0039] A sensorless control method for a dual three-phase permanent magnet synchronous motor that is robust to open-circuit faults includes the following steps:

[0040] Step 1: Design a sliding-mode observer and a phase-locked loop according to the dual d-q model of the dual three-phase permanent magnet synchronous motor. Considering the coupling between the two sets of three-phase windings of the motor, obtain the mathematical model of the coupling phase and decouple it to obtain the decoupled voltage in the generalized α-β stationary coordinate system, which is used as the voltage input of the sliding-mode observer to eliminate the coupling effect;

[0041] Step 2: When the dual three-phase permanent magnet synchronous motor is operating healthily, use any one of the two sets of three-phase windings of the motor to apply the sliding-mode observer designed in Step 1 to observe its back electromotive force, and extract the rotor position information through the phase-locked loop. The other set of three-phase windings is used as a backup;

[0042] Step 3: When a single-phase open-circuit fault occurs in the dual-three-phase permanent magnet synchronous motor, first determine in which set of the three-phase windings of the dual-three-phase permanent magnet synchronous motor the open-circuit fault occurs, and then adopt different back electromotive force observation strategies according to the judgment result;

[0043] When a single-phase open-circuit fault occurs in one set of the three-phase windings, use the healthy other set of three-phase windings to observe the back electromotive force, and the input of the sliding mode observer is the u″ of the healthy three-phase windings αβ and i αβ , where, u″ αβ is the generalized α, β-axis voltage of the healthy three-phase windings, i αβ is the α, β-axis current of the healthy three-phase windings, and the rotor position information in the back electromotive force is extracted through the phase-locked loop.

[0044] For example: 1) When a single-phase open-circuit fault occurs in the first set of three-phase windings (A, B, C), use the healthy second set of three-phase windings (D, E, F) to observe the back electromotive force, and the input of the sliding mode observer is u″ αβ2 and i αβ2 , and extract the rotor position information; where u″ αβ2 is the generalized α2, β2-axis voltage of the healthy second set of windings, i αβ2 is the α2, β2-axis current of the healthy second set of windings

[0045] 2) When a single-phase open-circuit fault occurs in the second set of three-phase windings (D, E, F), use the healthy first set of three-phase windings (A, B, C) to observe the back electromotive force, and the input of the sliding mode observer is u″ αβ1 and i αβ1 , and extract the rotor position information. Where u″ αβ1 is the generalized α1, β1-axis voltage of the healthy first set of windings, i αβ1 is the α1, β1-axis current of the healthy first set of windings

[0046] Among them, the first set of three-phase windings is the same as the second set of three-phase windings, without special meaning, only to distinguish the two sets of three-phase windings.

[0047] Taking the case where the F phase fails as an example in this embodiment, that is, the fault occurs in the second set of three-phase windings. After derivation, the voltage equation of the first set of three-phase windings of the surface-mounted DTP-PMSM in the α-β subspace is as follows, that is, the mathematical model for eliminating the coupling effect between the two sets of three-phase windings of the motor is:

[0048]

[0049] In the formula, u″ α1 , u″ β1 are the generalized α1, β1-axis voltages respectively, uα1 , u β1 are the voltages on the α1 and β1 axes respectively, p is the symbol of the differential operator, L dd and L qq are the mutual inductances of the d-axis and q-axis respectively, R s is the stator resistance, L d and L q are the self-inductances of the d-axis and q-axis respectively, i α1 , i β1 are the currents on the α1 and β1 axes respectively, i α2 , i β2 are the currents on the α2 and β2 axes respectively, i′ α2 , i′ α2 are the currents on the α2 and β2 axes after rotating clockwise by 30°, T park is the Park transformation matrix. ω is the electrical angular frequency, ψ fd is the rotor magnetic flux. Based on the above mathematical model of the first set of windings in the α-β subspace, the SMO is constructed as follows:

[0050]

[0051] In the formula, υ α1 and υ β1 are the estimated current and the control input of the SMO respectively, and h is the sliding mode gain.

[0052] In addition, in order to avoid jitter, a saturation function is used to replace the sign function in the traditional observer, where:

[0053]

[0054] In the formula, Δ is the boundary of the saturation function.

[0055] The topology of the SMO rotor position extraction method based on double d-q coordinate transformation proposed in this embodiment is as Figure 2 shown. Figure 2 Corresponding to Figure 1 the rotor position estimation part. When the motor is running healthily, the rotor position can be estimated by using any set of three-phase windings, and the other set of windings is used as a backup. When an OPF occurs (taking phase F as an example), after diagnosing that the open phase belongs to the second set of windings, the back electromotive force is observed by using the first set of healthy three-phase windings and the rotor position information is extracted. From the above analysis, it can be seen that the fault diagnosis algorithm only needs to diagnose which set of windings the fault occurs in, without knowing which specific phase it occurs in, thus greatly reducing the design difficulty of the fault diagnosis algorithm. Specific embodiment two:

[0057] This embodiment takes the case where a fault occurs in the first set of three-phase windings, that is, the three phases of A, B, and C. After derivation, the voltage equation of the second set of three-phase windings of the surface-mounted DTP-PMSM in the α-β subspace is as follows, that is, the mathematical model for eliminating the coupling effect between the two sets of three-phase windings of the motor is:

[0058]

[0059] In the formula, u″ α2 , u″ β2 are the generalized α2, β2 axis voltages respectively, u α2 , u β2 are the α2, β2 axis voltages respectively, p is the symbol of the differential operator, L dd and L qq are the d-axis and q-axis mutual inductances respectively, R s is the stator resistance, L d and L q are the d-axis and q-axis self-inductances respectively, i α2 , i β2 are the α2, β2 axis currents respectively, i α1 , i β1 are the α1, β1 axis currents respectively, i′ α1 , i′ α1 are the α1, β1 axis currents rotated counterclockwise by 30° respectively, T park is the Park transformation matrix. ω is the electrical angular frequency, ψ fd is the rotor flux linkage. Specific Embodiment 3:

[0061] This embodiment uses a dual three-phase permanent magnet synchronous motor with 10 poles, 12 slots, 750W, a rated speed of 600 rpm, and a rated load of 2.2 N·m for experiments. At the same time, to enhance the persuasiveness of the experiments, a traditional sensorless control method is used as the experimental control group.

[0062] As shown in Figure 3 (a) and (b), under the rated load of 600 rpm, the amplitudes of E α and E β of the method of the present invention basically remain unchanged after the occurrence of OPF_F (open circuit fault in phase F), which is a significant improvement compared with the traditional method.

[0063] As shown in Figure 3 (c) and Figure 3As shown in (d), at a rated load of 600 rpm, for the traditional method, the maximum estimated speed error of the rotor during a fault is about 11 rpm, while for the method of the present invention, the maximum estimated speed error of the rotor during a fault is about 8 rpm, and the fluctuation is smaller. For the traditional method, the maximum position speed error of the rotor during a fault is about 0.02π, while for the method of the present invention, the maximum estimated speed error of the rotor during a fault is about 0.08π. The experimental results show that: compared with the traditional method, the method of the present invention can greatly improve the rotor position estimation accuracy under open-circuit faults. Then, the experiment was carried out again by increasing the speed to 900 rpm.

[0064] As Figure 3 (e) and Figure 3 (f) show, at a rated load of 900 rpm, the amplitudes of E α and E β basically remain unchanged after the occurrence of OPF_F (open-circuit fault in phase F), which is a significant improvement compared with the traditional method.

[0065] As Figure 3 (g) and Figure 3 (h) show, at a rated load of 900 rpm, when a fault occurs, the estimation errors of both the traditional method and the method adopted in this embodiment are improved. Especially for the method of the present invention, the error before and after the fault basically remains unchanged. The experimental results show that the higher the motor speed, the better the performance of the method of the present invention when OPF_F occurs.

[0066] Figure 4 (a) and Figure 4 (b) show that for both the traditional method and the method of the present invention, during the process of changing the speed from 600 rpm to 900 rpm, the method of the present invention can achieve the same control effect as the traditional method. And Figure 4 (c) shows that when the speed of the faulty motor increases from 600 rpm to 900 rpm, the motor will get out of control under the traditional method, while under the method of the present invention, the motor is always under control, and the estimation error decreases with the increase of the speed. Therefore, the method of the present invention can greatly reduce the rotor position estimation error during open-circuit faults and significantly improve the system stability.

[0067] The above are only the preferred specific embodiments of the present invention. These specific embodiments are all different implementation manners based on the overall concept of the present invention, and the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A sensorless control method for a dual three-phase permanent magnet synchronous motor robust to open-circuit faults, characterized in that, It includes the following steps: Step 1: Design a sliding mode observer and a phase-locked loop according to the double d-q model of a dual three-phase permanent magnet synchronous motor. Considering the coupling between the two sets of three-phase windings of the motor, obtain the mathematical model of the coupling phase and decouple it to obtain the decoupled generalized α-β stationary coordinate system voltage, which is used as the voltage input of the sliding mode observer to eliminate the coupling effect; Step 2: When the dual three-phase permanent magnet synchronous motor operates healthily, use any one of the two sets of three-phase windings of the motor to apply the sliding mode observer designed in Step 1 to observe its back electromotive force, and extract the rotor position information through the phase-locked loop. The other set of three-phase windings is used as a backup; Step 3: When a single-phase open circuit fault occurs in the dual three-phase permanent magnet synchronous motor, first judge which set of the two sets of three-phase windings the open circuit fault of the dual three-phase permanent magnet synchronous motor occurs in, and then adopt different back electromotive force observation strategies according to the judgment result; When a single-phase open-circuit fault occurs in one of the three-phase windings, the healthy other three-phase winding is used to observe the back electromotive force, and the input of the sliding mode observer is the u″ of the healthy three-phase winding αβ and i αβ , where, u″ αβ is the generalized α, β-axis voltage of the healthy three-phase winding after decoupling the faulty three-phase winding, and i αβ is the α, β-axis current of the healthy three-phase winding, and the rotor position information in the back electromotive force is extracted through a phase-locked loop.

2. The sensorless control method for a dual three-phase permanent magnet synchronous motor robust to open-circuit faults according to claim 1, characterized in that, In Step 1, the phase difference between the corresponding phases of the two sets of three-phase windings is 30° electrical angle.

3. The sensorless control method for a dual three-phase permanent magnet synchronous motor robust to open circuit faults according to claim 1, characterized in that, In Step 3, the specific method for judging the single-phase open circuit fault of the dual three-phase permanent magnet synchronous motor is as follows: Use a four-dimensional vector controller to control the dual three-phase permanent magnet synchronous motor. The four-dimensional vector controller includes a speed closed loop and four current closed loops: d-axis, q-axis, x-axis, y-axis; Use four current sensors to monitor the current data of the four current closed loops, and obtain the actual six-phase current of the dual three-phase permanent magnet synchronous motor through the current data returned by the four current sensors. If the average current of a certain phase remains 0 within half an electrical cycle, it means that there is an open circuit fault in this set of three-phase windings.

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