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For permanent magnetic motors, the faults in inverter may cause serious mechanical vibration, winding overheating, and thermal demagnetisation for the magnets. Thus, this study addresses the problem of the electromagnetic field and temperature distributions for permanent magnet synchronous motor (PMSM) under open circuit fault (OCF) in the upper switch of one phase. Firstly, taking a 12.5 kW 2000 r/min PMSM as an example, the 2D transient electromagnetic field-circuit coupling calculation model is established. Then the flowing paths of the three-phase currents in inverter are analysed before and after the OCF in the upper switch of one phase. Next, by using the finite-element method, the current harmonics, the electromagnetic torque, the rotating speed, and the losses in PMSM are investigated. Simultaneously, direct current component and torque pulsation are also derived. Based on the 3D temperature field, the temperature distributions in different parts of PMSM also are comparatively studied before and after this fault. Moreover, the temperature of permanent magnets, which is the part most seriously affected by the temperature, are further analysed. Finally, calculation and experimental tests prove the accuracy of the theoretical analysis. The obtained conclusions may provide some references for the limit operation and effective diagnosis for inverter faults.

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In this paper, the effect of the line impedance difference between various inverters on power sharing with the traditional droop control method is fully analyzed. It reveals that the line impedance difference causes a significant reactive power error. An improved droop control method to eliminate the reactive power errors caused by the line impedance errors is proposed. In the proposed method, a voltage compensation determined by the actual reactive power error between the local inverter and the average one is added into the local voltage reference based on the CAN communication. Even when the communication is interrupted, the controller will operate with the last value of the average power, which still outperforms the traditional method. The effectiveness of the proposed control method is verified by simulation and experimental results, which show the proposed method possesses the better power sharing performance and dynamic response.

Multi-phase motors have attracted increasing attention in fields seeking high reliability, such as electric vehicles, ships, and rail transit, as they exhibit advantages, such as high reliability and fault tolerance. In this study, we consider a 12-phase permanent magnet synchronous motor (PMSM). First, a mathematical model of the 12-phase PMSM in the static coordinate system is established and the model is simplified according to the constraint condition of neutral point isolation. Second, according to the principle of invariant magnetomotive force under normal and fault conditions, two optimal control strategies of winding current, i.e. maximum torque output (MTO) and minimum copper consumption (MCC), are proposed. For a single-phase open-circuit fault, two optimization methods are used to reconstruct the residual phase current, such that the motor can maintain normal torque output and exhibit lower torque ripple under the fault state. Finally, system simulation and experimental research are conducted; the results verify the accuracy and feasibility of the fault-tolerant control strategy of the 12-phase PMSM proposed in this paper.