Single-phase dual-mode four-switch Buck-Boost Transformerless PV inverter with inherent leakage current elimination

This paper proposes a single-phase dual-mode four-switch Buck-Boost transformerless PV inverter with inherent ground leakage current elimination. Via directly connecting the grid neutral point to the PV positive terminal, the common mode (CM) voltage is clamped to be constant by the DC link capacitor. Thus, the CM leakage currents are eliminated completely. Moreover, the DC link voltage for the proposed inverter is required to be only higher than the amplitude of the grid voltage, instead of higher than twice of the amplitude of the grid voltage for the half-bridge-based inverter. There are two operation modes for the proposed inverter: Buck mode for the negative half line cycle and Buck-Boost mode for the positive half line cycle. Single stage energy process is achieved in both two operation modes for achieving high efficiency. The smooth mode transition is realized by the proposed dual-mode dual-carrier unipolar sinusoidal pulse-width-modulation (SPWM). Besides, since this PV inverter only uses four switches and one main inductor, low cost is achieved by this inverter. In summary, the proposed PV inverter achieves low leakage current, high efficiency, high density, low cost, and non-unity power factor capability. Finally, the simulation results verify the concepts and demonstrate the performance of the topology, the modulation and the control strategy.