Fault Tolerant Operation of T-NPC Three-Level Asymmetric Six-Phase PMSM Drives Based on Direct Torque Control

In this paper, a novel remedial direct torque control (DTC) scheme is proposed for T type NPC (T-NPC) three-level asymmetric six-phase PMSM drives under open-phase faults. A simplified space vector modulation (SVM) is designed and applied for the DTC controlled asymmetric six-phase drive, in such a way that both good current harmonic performance and small DC link voltage fluctuation are available. The relationship between the stator fluxes and the stator voltages including the faulty phase is derived after the fault. Thus, the perturbation could be added to the voltage references, and the control system under is kept almost unchanged after fault. The experiments on a laboratory prototype are carried out to verify that the proposed remedial scheme can provide smooth torque while good harmonic performance without changing the control structure.