High-efficiency bidirectional AC-DC converter for energy storage systems

A high-efficient bidirectional ac-dc converter is proposed for energy storage system. The proposed converter can transfer both active and reactive power between ac grid and dc sources. The proposed converter exhibits two distinct merits: (1) no shoot-through issues because the phase leg does not contain series connected switches, (2) the reverse recovery dissipation of the power switch is greatly reduced because the freewheeling current does not flow through the body diode of power MOSFET. Along with the admittance compensation, a quasi proportional-resonant controller has been designed to significantly increase the loop gain at the fundamental frequency, while maintaining enough phase margins. The proposed controller has been simulated and implemented in a FPGA-based 1-kW bidirectional ac-dc converter prototype. Experimental results validate the design of the proposed high-efficiency high-performance converter.