DC-Link Current Ripple Reduction Method for the Reduced Switch Count Three-Level Inverter With Unbalanced Neutral-Point Voltages

The reduced switch count three-level inverter (RSC TLI) can reduce the number of power switches, but the conventional space vector modulation (SVM) method generates the large dc-link current ripple and reduces the dc-link capacitor reliability. This article proposes a novel dc-link current ripple reduction method, which applies to both balanced and unbalanced neutral-point (NP) voltage (NPV) conditions. First, the duty-cycle calculation of the conventional SVM method is introduced. To realize the dc-link current ripple reduction, the region division method is optimized by analyzing the range of the duty-cycle distribution factor and combining the magnitude of output current. In doing so, the calculating complexity of duty cycles is reduced. Second, a deadbeat control (DBC) method is designed for accurate and fast separate control of capacitor voltages. At last, appropriate switching sequences are arranged. Compared with the conventional SVM method, the dc-link current ripple of the proposed method is reduced by one-fourth and two-fifths in the high- and low-modulation indices, respectively, and maintains the rewarding quality of output currents with balanced and unbalanced NPVs. The feasibility and effectiveness of the proposed method are verified by simulations and experiments.