Active Switching Strategy of Dual Sliding Mode Observer for Dual Three-phase PMSM under Single-phase Open-circuit Fault

Dual three-phase permanent magnet synchronous motors are of significant application value in low-altitude economy fields such as electric vertical take-off and landing aircraft due to their high power density, low torque ripple, and strong fault-tolerant capability. However, inverter single-phase open-circuit faults can disrupt the symmetry of motor control, leading to degraded or even failed performance of traditional sensorless control. To address this issue, an active switching fault-tolerant control strategy based on dual sliding mode observers is proposed. Firstly, a motor model in the dual dq coordinate system under single-phase open-circuit fault is established, and the distortion mechanism of voltage and current signals is analyzed. Secondly, two independent sliding mode observers are designed to estimate the back electromotive force for the two sets of windings separately, with the 30° phase difference eliminated through coordinate rotation. Finally, a fault diagnosis method based on the comparison of output voltage amplitudes from the controller is proposed to achieve real-time fault detection and autonomous observer switching. Experimental results show that this active switching strategy can accurately identify the fault phase location under single-phase open-circuit fault and autonomously switch to the sliding mode observer of the healthy winding. This ensures continuous estimation of rotor position and speed after the fault, significantly enhancing the fault tolerance and robustness of the system under sensorless operation.