Enhancing PMSM Drive Performance Under Open-Phase Fault Using Fractional-Order Controllers

Open-phase faults (OPFs) represent a major challenge in PMSM drive systems due to the induced current imbalance, torque ripple, and degradation in speed regulation performance. Although fractional-order controllers and model predictive control have been extensively investigated for PMSM drives, their individual application does not directly address the coordinated control requirements arising from post-fault operation. Therefore, this paper develops a coordinated fault-tolerant PMSM drive framework in which open-phase fault detection, neutral-point reconfiguration, and fractional-order PI (FO-PI) speed regulation are integrated within a unified post-fault control architecture. A mathematical PMSM model covering both healthy and open-phase operating conditions is established to capture the altered post-fault dynamics and provide the basis for fault diagnosis and controller design. In contrast to conventional approaches in which fractional-order speed control is primarily designed for healthy operation, the proposed controller parameters are obtained through bounded numerical optimization while explicitly considering the post-fault operating condition. The proposed framework is evaluated in MATLAB/Simulink under multiple operating speeds and compared with the conventional PI controller using the integral absolute error (IAE) as a quantitative performance metric. The optimized FO-PI controller reduces the post-fault IAE by 27.0% at 1000 rpm and approximately 51.0% at 800 rpm compared with the conventional PI controller. For further validation, an FO-PID controller is included as an advanced fractional-order benchmark, allowing the performance of the proposed FO-PI design to be assessed against a controller with additional tuning degrees of freedom under the corresponding operating condition. The results demonstrate that the coordinated diagnosis reconfiguration fractional controller design framework improves post-fault PMSM speed regulation and maintains stable operation following an open-phase fault.