Simultaneous Current Ripple and Switching Loss Reduction for Three-Level T-Type Inverter Under Switch Fault Conditions

Abstract

Three-level T-type inverter (3LT2I) plays an essential role in meeting the requirements of high reliability, efficiency, and power density in electrified ships. As these three objectives are mutually interrelated, existing strategies cannot realize them simultaneously. Therefore, a simultaneous current ripple and switching loss reduction strategy for 3LT2I under switch fault conditions is proposed in this article. Based on discontinuous pulsewidth modulation (DPWM), partial clamping modes are abandoned and the carrier is modified to avoid using the impossible switching states caused by switch fault, which realizes fault-tolerant control (FTC) with the switching loss reduction. Then, the new relationship between the current ripple and clamping mode under switch fault conditions is quantitatively derived, which is used to select the optimal candidate clamping mode for reducing the current ripple. Moreover, when the neutral-point (NP) voltage exceeds the threshold range, the candidate clamping mode is further selected according to the NP current to balance the NP voltage. By simultaneously realizing FTC, switching loss reduction, current ripple reduction, and NP voltage control, the three objectives mentioned above are realized. The experimental results validate the effectiveness of the proposed strategy.