Flux-Weakening Scheme for Four-Switch Inverter-Fed IM Drives With Optimized Overmodulation-Based Modulated Predictive Torque Control

Four-switch three-phase inverter (FSTPI) has been considered as a promising fault-tolerant topology for six-switch three-phase inverter (SSTPI) with an open-phase fault. However, the maximum linear voltage of FSTPI is reduced by half compared to SSTPI due to the reduced power switches, which limits the high-speed operation capability. In this article, a flux-weakening scheme for the FSTPI-fed induction motor (IM) using optimized overmodulation strategy-based modulated predictive torque control (M-PTC) is proposed. Therein, a voltage closed-loop flux-weakening control method considering the dc-link capacitor voltage offset (CVO) is developed to suppress the ripple in stator flux. An M-PTC strategy is proposed to handle the nonlinearities and constraints in IM drives, together with a two-long-voltage-vector-based pre-excitation scheme designed for maintaining the minimum CVO during the initial startup process. To increase the utilization rate of the dc-link voltage and the maximum output torque in flux-weakening region, an optimized overmodulation strategy is proposed to extend the available voltage from inscribed circle to quadrilateral region. Extensive experimental studies are carried out to verify the effectiveness of the proposed method.