Common-Ground Type Switching Step-Up/Step-Down VSI for Grid-Connected PV System

Microinverter without transformer structure is widely used in photovoltaic grid-connected systems because of its low cost and high efficiency, but the challenge is to solve the common-mode leakage current caused by common-mode voltage. This paper studies a novel transformerless dual-mode voltage source inverter (VSI) in which the common ground structure short-circuits the parasitic capacitance and theoretically completely eliminates leakage currents. The inverter consists of a switching-buck-boost (SBB) module integrated with an LC filter network and has a good symmetry of the output waveform. The proposed topology features a wide input voltage range to meet the grid voltage gain, a compact structure, and a simple modulation strategy. Meanwhile, the SBB module allows for soft charging and current stress control within the permissible range. The structural characteristics and operating principle are described in detail, a mathematical model is developed and a closed-loop compensator is designed. The results show the feasibility and good performance of the proposed VSI.