Fault-Tolerant Control Strategy for PMSMs Under Open-Switch Fault in the Flux-Weakening Region

This paper proposes a fault-tolerant control (FTC) strategy for three-phase permanent magnet synchronous motors (PMSMs) with regenerating operation in the flux-weakening region under an open-switch fault. The considered fault is that the switch is permanently open, but the body diode conducts, causing the inverter output voltage region to vary depending on the current direction. Conventional voltage projection methods perform adequately at low speeds but can cause overcurrent at high speeds due to the high stator flux voltage. To overcome this problem, the proposed method imposes a magnitude limit on the voltage command. In the stationary reference frame, the projected voltage command is restricted to satisfy the current constraint under fault conditions. When the stator flux voltage exceeds the feasible boundary, the control shifts to the synchronous reference frame. In this stage, a recovery-oriented voltage command is applied to restore sufficient voltage margin and enable a smooth transition back to normal operation. This coordinated mechanism ensures stable operation within current limits, particularly during regenerative braking, while adaptively adjusting the voltage vector according to the prevailing fault condition. Simulation and experimental results confirm the effectiveness of the proposed method in suppressing overcurrent, minimizing distortion, and maintaining reliable performance across a wide range of operating scenarios.