I. Introduction
To alleviate the energy crisis and environmental pollution, renewable energy generation has been widely applied in recent years. However, the output power of renewable energy sources in the dc microgrid system is unstable because of the external environment. Thus, the energy storage system is critical to guarantee the power balance of the dc bus in the microgrid [1]. A bidirectional dc–dc converter (BDC), which has the function of bidirectional power flow, is a key interface device for storage elements, such as battery and supercapacitor. In practice, the output voltage of a battery or supercapacitor is usually low [2]. Although a series connection can be adopted among individual cells to meet the required voltage, a voltage equalization circuit is necessary for the battery pack [3]. As a solution, BDCs with high voltage conversion ratio (VCR) are desired to connect the low-voltage battery to the high-voltage bus.