Fault-Tolerant Control Strategy in Extended Torque Operation Range With Relaxed Torque Ripple Constraints for Dual Three-Phase PMSM

This article investigates fault-tolerant control (FTC) of a dual three-phase permanent magnet synchronous motor (DT-PMSM) with one phase under open-circuit fault (OCF). Unlike existing approaches in the literature, the proposed method extends the torque operation range (TOR) by relaxing the conventional constraint of zero torque ripple. A FTC strategy based on 2^nd-order harmonic current injection is developed to achieve extended TOR with minimum ripple (ETOR-MR). Two winding configurations of DT-PMSMs are considered and investigated in this study: isolated neutral point (2N) and connected neutral point (1N). In the case of 2N configuration, the proposed algorithm increases the TOR from 57.74% to 78.85% of rated torque; for the 1N configuration, the TOR is improved from 69.94% to 80.07%. Although torque ripple is inevitably introduced throughout the extended range, it is minimized by the proposed algorithm. At the same time, sinusoidal current waveforms are maintained in all healthy phases, ensuring minimal copper losses under fault conditions. By constructing the optimization problem with these constraints, analytical solution is derived for the 2N configuration, while numerical solution is obtained for implementation in the 1N case. The effectiveness of the proposed approach is validated through experimental testing on a 4 kW DT-PMSM test bench.