Analysis and comparison of different grid-tied transformerless inverters for PV system

The unipolar sinusoidal pulse width modulation (SPWM) full-bridge (FB) transformerless photovoltaic (PV) inverter can achieve high efficiency by using super-junction MOSFETs together with silicon carbide (SiC) diodes. However, the MOSFETs are limited to use in transformerless PV inverter due to the low reverse recovery characteristics of the body diode. In this paper, a new transformerless PV inverter topology for single-phase grid-tied operation is proposed using super-junction MOSFETs as no reverse recovery issues are required for the main power switches. The added clamping branch clamps the freewheeling voltage at the half of dc input voltage during the freewheeling period. As a result, the common mode (CM) voltage kept constant during the whole grid period that reduces the leakage current significantly. In addition, dead time is not necessary at both the high frequency commutation and the grid zero crossing instant, results low current distortion at output. Finally, a 1kw prototype is built and tested to verify the theoretical analysis. The experimental results show 98.6% maximum efficiency and 98.44% European efficiency on the 1kw prototype circuit with 20 kHz switching frequency.