Bidirectional Step-up/down Flyback Converter for Energy Storage System

As the renewable energy generation develops, its fluctuation and intermittency have to be considered. Configuration of energy storage system is a solution, which can balance the power produced and the power consumed. As the interface between energy storage system and the grid, bidirectional DC-DC converter is required. However, the conversion ratio of commonly-used nonisolated bidirectional converter is not high enough to connect the battery to the grid. Canonical bidirectional flyback converter is isolated and able to attain high conversion ratio, but the leakage inductance of the transformer causes problems. In this paper, a bidirectional step-up/down flyback converter for energy storage system is proposed, which consists of a step-up/down cell and a bidirectional flyback cell in cascade. The step-up/down cell can achieve high conversion ratio so that the turns ratio of the transformer can be reduced, leading to lower leakage inductance. Its operating principles in forward mode and reverse mode are discussed in detail, and the overall conversion ratio and the stresses of MOSFETs are deduced. The process of parameter design is introduced, and the simulation based on the designed parameters is carried out. A 50W prototype is produced and tested, and the results generally correspond with theoretical analysis, which verifies the utility of the proposed converter.