A zero-sequence current suppression method for pentacle-wired five-phase PMSMs under a single-phase open fault

The zero-sequence circulating current (ZSCC) becomes prominent in the single-phase open-circuit fault of a pentacle-wired five-phase motor, and this phenomenon can lead to phase current distortion and torque fluctuation. To address this issue, a linear approximation control method is proposed, and proportional-integral (PI) control is used to suppress the alternating ZSCC. Firstly, a decoupling fault-tolerant control scheme for a pentacle-wired five-phase motor is introduced. This scheme extends the existing fault-tolerant control for star-wired five-phase motors by developing additional line-to-phase transformation matrices for the phase current and voltage. Then, a nonlinear mathematical relationship between ZSCC and zero-sequence electromagnetic torque is derived, and the nonlinear zero-sequence model is linearized using a subdivision method based on the rotor position. Combined with a multi-dimensional PI controller, ZSCC suppression is achieved. Finally, simulation and experimental results suggest that ZSCC exhibits an alternating characteristic with a significant amplitude oscillating at the fundamental frequency before suppression. ZSCC is effectively eliminated after the suppression method is applied. Also, the phase currents return to normal and can recover from the prior condition of severe imbalance and over-large amplitude, and the torque fluctuation issue is mitigated. In conclusion, when a single-phase open-circuit fault occurs in a pentacle-wired five-phase motor, the fault-tolerant control method with active suppression of ZSCC can be used to mitigate the phase current distortion and torque fluctuation.