Enhanced Four-Port-based DAB Converter for Interlinking and Balancing Bipolar DC Buses of DC Distribution Systems

Abstract

Bipolar DC distribution systems have become an attractive solution having various voltage levels and higher system reliability compared with a unipolar system. However, a voltage balancer is required to balance the bipolar voltage levels. The additional voltage balancer can degrade the power conversion efficiency and power density of a DC system. To solve the above issue, an enhanced four-port-based dual-active-bridge (DAB) converter is proposed, which can balance and interlink two bipolar DC buses using a single power stage without additional voltage balancers. To obtain the voltage balancing capability, a power flow control strategy is proposed to compensate for the unbalanced power flows. The proposed strategy can be implemented by the proposed converter using its three independent power flow capabilities. Moreover, a full-load range ZVS modulation is proposed to enhance the power conversion efficiency, which can obtain the ZVS capability of all the power switches over the entire load range. Finally, a 3-kW laboratory prototype is implemented to verify the theoretical analysis and the effectiveness of the proposed converter.