The Indirect Correction Method of Virtual Vectors for Dual Three-Phase Permanent Magnet Synchronous Motors under the Open-Phase Fault and Its Application in the Direct Torque Control
Zhou Changpan1, Liu Haifeng1, Jing Guoxiu2, Liu Tan1, Sun Xiangdong1
1. School of Electrical Engineering Xi’an University of Technology Xi’an 710054 China; 2. College of Information Science and Engineering Northeastern University Shenyang 110819 China
Abstract：Multiphase machines have low voltage, high power, low torque pulsation, and good fault tolerance, which have good application prospects in high-power driving applications such as electric vehicles, marine electric propulsion, and wind power generation. The phase-shifted 30° dual three-phase motor (the asymmetric six-phase motor) has a greater application advantage due to the cancellation of the sixth torque harmonic among various multiphase machines. The high fault-tolerant capability is an important application feature of multiphase machines. Various open-circuit and short-circuit faults in the machine drive system can be converted into open-phase faults through fault isolation. Therefore, the research of fault-tolerant control strategies for multiphase machines is mainly focused on the open-phase fault. Currently, the common control strategies for fault-tolerant operation include field-oriented control (FOC), model predictive control, and direct torque control (DTC). Among them, DTC does not need complex coordinate transformation, which weakens the influence of motor parameter changes on the control effect. In addition, DTC also has the advantages of a simple structure and fast torque response. Thus, it is widely researched in the fault-tolerant control of multi-phase motors. Firstly, the basic voltage vectors in the direct torque control for dual three-phase permanent magnet synchronous motor (PMSM) drives must be modified. Using the modified virtual vectors for DTC, the harmonic currents in the z1-z2 sub-plane can be suppressed significantly. When an open-phase fault occurs, the voltage vectors need to be modified again. The voltage vector distribution in the open-phase fault operation is introduced. An indirect correction method of virtual voltage vectors is proposed under the single-phase open-circuit fault, and the amplitudes of the virtual voltage vectors are maximized. Moreover, the single-phase open-circuit fault-tolerant direct torque control strategy for a dual three-phase motor based on virtual voltage vectors is constructed. Its stator flux chain partition and switching table selection rules are the same as the dual three-phase motor under healthy operation. The only difference is that the amplitudes of twelve virtual vectors are reduced in the open-phase fault operation. Experimental verification was carried out on a surface-mounted dual three-phase PMSM. The parameters of the dual three-phase PMSM are listed as follows: Pn=4, Rs=0.5Ω, LD=2.04mH, LQ=2.04mH, and ψfd=0.12Wb. The DC bus voltage is 200V. The switching frequency is 10kHz with a dead time of 2μs. Harmonic currents and torque pulsations in different control methods are compared and analyzed. The THD of phase current A is 5.6%, and the torque pulsation is 1N·m in the healthy DTC operation of dual three-phase PMSM. The THD of phase current A is 141.8%, and the torque pulsation is 1.7N·m under the single-phase open-circuit fault of dual three-phase PMSM when the original vectors are used. The THD of phase current A is 7.8%, and the torque pulsation is 1.2N·m in the open-phase fault DTC operation when the same amplitude virtual vectors are used. The THD of phase current A is 15.7%, and the torque pulsation is 1.4N·m in the open-phase fault DTC operation when the maximum amplitude virtual vectors are used. The amplitudes of the maximum amplitude virtual vectors are not equal, but the DC bus voltage utilization rate is improved. Compared with the same amplitude virtual vectors, the THD of phase currents and the torque pulsation are larger when the maximum amplitude virtual vectors are used. The same amplitude virtual vectors can be used under low speed and light load conditions for low harmonic currents and torque pulsations. The maximum amplitude virtual vectors can be used under high speed and heavy load conditions for larger speed and torque output. The following conclusions can be drawn from the theoretical analysis and experimental results: ① An indirect correction method of virtual voltage vectors is proposed under the single-phase open-circuit fault, and the amplitudes of the virtual voltage vectors are maximized. ② The proposed control strategy ensures that the sector distribution and the selection rule of the look-up tables after the single-phase open-circuit fault are consistent with those in the healthy operation, simplifying the control process. ③ The virtual vectors indirect correction method proposed in this paper can also be extended to other multiphase motors, such as five-phase motors. And be applied to two-phase faults of motors.
周长攀, 刘海峰, 景国秀, 刘坛, 孙向东. 双三相永磁同步电机缺相容错运行虚拟矢量间接修正方法及其在直接转矩控制中应用[J]. 电工技术学报, 2023, 38(2): 451-464.
Zhou Changpan, Liu Haifeng, Jing Guoxiu, Liu Tan, Sun Xiangdong. The Indirect Correction Method of Virtual Vectors for Dual Three-Phase Permanent Magnet Synchronous Motors under the Open-Phase Fault and Its Application in the Direct Torque Control. Transactions of China Electrotechnical Society, 2023, 38(2): 451-464.
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2023, Vol. 38 
