Mitigation of Dead-Time Effects in the FB-CCV Transformerless PV Inverter

Abstract

This article analyzes dead-time effects in the full-bridge inverter topology with constant common-mode voltage (FB-CCV) for transformerless grid-connected photovoltaic (PV) applications and proposes a modulation strategy to mitigate the resulting output-voltage distortions, common-mode transients, and power losses. Although midpoint-clamped transformerless inverters are designed to keep the common-mode voltage nearly constant, the mandatory dead time can force the grid current through the antiparallel diodes of the H-bridge switches, producing output-voltage spikes during freewheeling intervals. These transient states increase voltage stress, contribute to switching losses and can excite high-frequency leakage-current transients through the parasitic capacitance of the PV array. The proposed modulation preserves the appropriate freewheeling path during dead-time intervals by keeping the corresponding freewheeling switch active throughout each half-cycle and using the sign of the grid-voltage derivative to select the preferential clamping path. Experimental results show that the proposed strategy substantially suppresses these output-voltage spikes over the evaluated dead-time range. The proposed modulation also reduces the severity of high-frequency common-mode transients, lowers the high-frequency leakage-current contribution and decreases both the estimated semiconductor losses and the measured inverter-stage power losses. These results demonstrate that the proposed modulation mitigates dead-time-induced voltage distortions, attenuates high-frequency common-mode transient activity and reduces the power losses of the FB-CCV inverter.