Bidirectional Soft-Switching Series-Resonant Converter With Simple PWM Control and Load-Independent Voltage-Gain Characteristics for Energy Storage System in DC Microgrids

A fixed frequency operated bidirectional series-resonant (BSR) converter is proposed for energy storage system in dc microgrid. Simple pulsewidth modulation (PWM) control is applied to the proposed converter to regulate the power flows and achieve the following attractive features: 1) the voltage gain of the converter is only determined by the effective duty cycles of switches and has nothing to do with the amplitude and direction of the transferred power, which is a significant innovation and improvement in comparison with most of the existing resonant converters; 2) theoretically, the normalized voltage gain can be regulated from zero to infinite, which means the proposed BSR converter is a Buck–Boost converter and suitable for wide voltage range applications; 3) the direction of power flow and the operation mode, i.e., the forward or backward mode, can be changed automatically and smoothly with the simple PWM control; and 4) zero-voltage switching turn-on is achieved for all the active switches within the entire operation range. Operation principles, control strategies, characteristics, and design considerations of the proposed BSR are analyzed. A 1.6 kW prototype is built and tested to evaluate the feasibility of the proposed converter.