Common-Mode Filter for Transformer-Less Split-Phase Neutral Grounded Inverter

A three-leg full-bridge inverter is conventionally used to generate split-phase AC voltage. If the neutral phase of such an inverter is grounded, then parasitic currents of significant magnitude appear in the ground circuit. This issue arises primarily due to the presence of high-frequency common-mode voltage between the output AC terminals and the DC-bus terminals. In this paper, split DC-bus capacitors are introduced in the conventional inverter circuit to attenuate the common-mode switching voltage. The addition of the capacitive filter forms a second-order low-pass filter for common-mode voltage and attenuates the magnitude of the switching-frequency component of common-mode voltage by around 40 dB. The proposed inverter is thereby able to generate a transformer-less neutral grounded split-phase AC voltage supply for an off-grid application. The simulation and experimental results of a 12 kW lab prototype are presented for verifying the proposed converter circuit topology.