A novel flying capacitor transformerless inverter for single-phase grid connected solar photovoltaic system

This paper proposes a new single-phase flying capacitor transformerless PV inverter for grid-connected photovoltaic (PV) systems. The neutral of the grid can be directly connected to the negative terminal of the source (PV). It consists of four power switches, one diode, one capacitor and a small filter at the output stage. A simple Unipolar Sinusoidal Pulse-Width Modulation (SPWM) technique is used to modulate the inverter to minimize switching loss, output current ripple and filter requirements. The main advantages of the new inverter topology are: (1) the negative polarity of the PV is directly connected to the grid, so no leakage current, (2) voltage stress of all switches are the same and equal to the dc-link voltage, (3) reactive power can be send to the grid, so no problem of reactive power compensation (4) peak of output ac voltage is equal to input dc-voltage (unlike NPC, ANPC and some topologies, which requires two times of the peak ac-voltage magnitude) and, (5) the flying capacitor charges every switching cycle, which reduces the size of the required capacitor with switching frequency. In addition, industry standard half bridge module can be used in the new inverter without any modification. Experimental results of 1 kW prototype are presented at the end of the paper to prove the concept and theoretical analysis of the proposed transformerless inverter. The peak efficiency of the inverter at a full load is 99.2%.