Bilateral Common-mode Voltage Injection Method with Minimized Low-frequency Ripple Buffering of AC/AC Solid-State Transformer

Due to its phase-separate structure, the cascaded H-bridge-based solid-state transformer (SST) suffers from low-frequency ripple, necessitating bulky DC-Link capacitors. This paper introduces a ripple power buffering method employing bilateral common-mode voltage (CMV) injection, enabling full-range low-ripple operation irrespective of grid phase difference and power factor. Three CMV generation strategies, based on analytical models and numerical optimization, are proposed and compared. Simulation results demonstrate up to 73% ripple voltage suppression across the entire operating range.