Influence of direct-connected inverter with one power switch open circuit fault on electromagnetic field and temperature field of permanent magnet synchronous motor

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.