A Solution for the Full-bridge Grid-tie Inverter Using Single Virtual Ground Capacitor with UPWM

A single-phase transformerless full-bridge (FB) photovoltaic (PV) grid-tie inverter is presented. It achieves the ground leakage current mitigation by single Virtual Ground (VG) capacitor without extra switching devices. A hybrid pulsewidth modulation (HPWM) scheme is proposed to profile the output current and prevent sudden changes in the common-mode voltage. The HPWM is effectively the same as unipolar PWM (UPWM), but with soft voltage transition modulation (SVTM) introduced around the zero crossings. Apart from low switching losses, the output filter is implemented with a minimum number of components to achieve high attenuation of ripple current. Three commonly used PWM schemes for PV inverters are described. The intrinsic reason for oscillation phenomenon in bridgeless inverters with single VG capacitor is presented. A 340W, 380Vdc / 110Vac, 50Hz prototype has been built and evaluated.