In this study, a direct torque control (DTC) strategy based on a novel switching table for induction motor drives fed by the eight-switch three-phase inverter (ESTPI), which is the post-fault reconfigured topology for the three-level neutral-pointclamped inverter with the open-circuit fault occurring in a leg, is proposed to reduce the torque ripple and suppress the dc-link capacitor voltages offset. The influence of each basic voltage vector provided by the ESTPI on the stator flux, the electromagnetic torque and the dc-link capacitor voltages is analysed in detail, and the causes of the torque ripple and the capacitor voltages offset are also revealed. To suppress the dc-link capacitor voltages offset, a hysteresis comparator is added to regulate the dc-link capacitor voltages. Based on that, an optimised switching table to achieve not only torque ripple reduction but also dc-link capacitor voltages offset suppression is proposed. The feasibility and the effectiveness of the proposed DTC strategy are verified by simulations and experimental results.

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A model predictive current control scheme with dc-link capacitor voltages fluctuation suppression for the four-switch three-phase rectifier (FSTPR) in balanced grids is presented. The proposed control scheme is a type of the finite-control-set model predictive control scheme and is based on the discrete-time model of the system. From this model, the values of input currents and dc-link capacitor voltages are predicted for all switching states of the FSTPR. On the basis of a predefined cost function, the switching state, which minimises the errors between input currents and their references as well as the difference between two dc-link capacitor voltages at the next sampling instant, is selected. Simulation results are presented to confirm the effectiveness of the proposed control scheme.

The relationship between common-mode voltages (CMVs) and switching states in the post-fault reconfigured topology of the threelevel neutral-point-clamped inverter with open-circuit fault in a leg, which is named eight-switch three-phase inverter (ESTPI), is revealed, and based on that, two modified space vector pulse-width modulation (M-SVPWM) algorithms for the CMV reduction in the ESTPI are proposed. The maximum CMV of the ESTPI with two proposed M-SVPWM algorithms is only half of that with two conventional SVPWM algorithms. Experimental results have shown the effectiveness of two proposed M-SVPWM algorithms.

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