A Ripple-Free Capacitor-Less Design with Unbalanced Operating Points for Input-Parallel Output-Series DAB Fed Single-Phase VSI

The low-frequency pulsating power inherent in single-phase system is harmful to the renewable source and output power quality. All existing solutions have to introduce extra components or bulky electrolytic capacitors. In this paper, Input-parallel Output-series DAB with unbalanced operating points (UOP) is adopted as the front-end dc/dc converter. The low-frequency power can be fully compensated by the very small output capacitors, and both the input current and dc bus voltage are ripple-free. A comprehensive comparison between UOP and traditional method is conducted based on simulation results. It shows that fifty-three times dc bus capacitance requirement can be reduced using the UOP method. Furthermore, a parameters optimization scheme based on semiconductor current stress is proposed and tested.