Bidirectional LLC resonant converter for energy storage applications

This paper proposes a new LLC resonant DC-DC topology with bidirectional power flow capability. All the switches in the proposed topology can achieve zero voltage switching (ZVS) at turn on, and zero current switching (ZCS) is achieved for the output side switches at turn off. Compared with the traditional bidirectional dual active bridge (DAB) converter, the turn off current is greatly reduced, and the frequency modulation control scheme can almost eliminate the large circulating energy. Therefore, the conversion efficiency can be much improved, which makes it quite attractive in energy storage applications. The output characteristic of the proposed LLC converter is different from the conventional unidirectional LLC resonant converter. A new analytical model is also proposed in this paper. The detailed operating principle and performance of the proposed topology are analyzed. And a 1 kW prototype is built to verify the theoretical analysis. Over 98% efficiency is achieved base on the prototype.