Capacitor Voltage Balancing Control for a Novel 5-Level Dual Active Bridge Converter

Multilevel technology is an attractive solution to increase the cost effectiveness and power density of dc solid state transformers. In this article, a novel five-level (5L) dual active bridge (DAB) converter topology is proposed. By stacking two neutral-point-clamped (NPC) converters at the primary side, the proposed topology could quadruple the input dc-bus voltage of a conventional two-level (2L) DAB converter. Besides, by analyzing the working principle of the 5L-DAB converter, a voltage balancing control method is carried out. With the aid of the voltage balancing method, voltages of the four series-connected dc-bus capacitors in the 5L-DAB converter can be actively balanced, guaranteeing safe operation voltage for all the semiconductor switches. After that, the operation range of the proposed voltage balancing method is derived by theoretical analysis. Finally, the performance of the proposed converter topology and voltage balancing method have been verified by experimental results.