Modulation and Capacitor Voltage Balancing Control of a Hybrid Four-Level DAB with Reduced Switches

Medium-voltage DC (MVDC) distribution network on ship has a strong requirement for high-efficiency and power density DC power electronic transformer (PET). The multi-level dual active bridge (DAB) converter can meet above requirement while withstanding the voltage level of MVDC distribution network. This paper proposes a four-level DAB based on simplified DNPC, which has less devices and thus lower cost. The proposed multi-level DAB works in Quasi-2-1eve1 (Q2L) modulation, which ensures higher power-transferring ability and acceptable dv/dt performance. Capacitor voltage balancing is controlled by single active half-bridge with proposed method. Simulation results has proved the feasibility of proposed topology and validity of proposed modulation and control methods.