Multicarrier-based Capacitor Voltage Balancing Approach for a New Four-Level Multilevel Converter

This paper proposes a new four-level multilevel converter for medium-voltage, high-power applications. The proposed topology requires a lesser number of components, eliminates series connection of devices, and suitable for back-to-back operation due to the presence of common DC-link. Furthermore, the proposed topology does not require isolated DC source thereby the phase-shifting transformer can be eliminated to reduce the system cost and size. In addition, a simple capacitor voltage balancing approach based on multicarrier-based pulse width modulation scheme is proposed. The proposed approach selects a right switching state to maintain each flying capacitor voltage at their nominal value by considering the current direction, instantaneous value of capacitor voltage, and voltage level. The performance of the proposed four-level multilevel converter and voltage balancing approach is verified through simulations at steady-state and transient operating conditions.