A Nonisolated Bidirectional DC–DC Converter With High Voltage Conversion Ratio Based on Coupled Inductor and Switched Capacitor

In this article, a nonisolated bidirectional dc-dc converter is proposed based on coupled inductor (CL) and switched capacitor (SC). The converter can achieve a high voltage conversion ratio (VCR) by using CL and SC. The CL is operated not only as a filter inductor to regulate voltage but also as a transformer to improve the VCR. Furthermore, the voltage stresses of capacitors and switches are reduced by introducing SC structure. The pulsewidth modulation plus phase-shift control is employed, where the duty cycle is used to ensure that the voltages of two sides are matched and the phase-shift angle is used to control the direction and amount of power flow. In addition, all the switches can achieve zero voltage switching in both forward and backward modes under a wide operating range, which can improve the efficiency of power conversion. The operating principle and steady-state analysis are examined, and a 400-W prototype is designed to verify the validity of the proposed converter.

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.