An Asymmetric Modulation Strategy for a Single-Phase Single-Stage AC-DC Converter

Single-stage dual-active-bridge (DAB) ac-dc converter features higher power density and reliability compared to two-stage ac-dc conversion system. This paper presents an asymmetric modulation method for a single-stage ac-dc DAB converter. The modulation method proposed in this paper utilizes three degrees of control freedom with fixed switching frequency to minimize the peak-to-peak value of the transformer leakage inductor current over the full range of the fundamental ac-side voltage. The control variables can be calculated in real-time according to the optimization procedure. Compared to conventional one and two-degrees-of-freedom modulation methods, the proposed method can reduce the current stress of the switching devices and improve the efficiency of the power conversion system. Simulation results validate the effectiveness of the proposed method.