Single-Phase Photovoltaic Inverters with Common-Ground and Wide Buck-Boost Voltage Operation

The output voltage of a photovoltaic panel is greatly affected by irradiance, temperature, shading, and so on. A buck-boost type inverter is therefore required to accommodate the wide fluctuations in dc voltage. This paper proposes a class of single-phase, single-stage buck-boost inverters employing five switches (implemented using power MOSFETs with external fast recovery diodes) to provide buck-boost operation for wide variations in PV output voltage. The proposed inverters are immune from current shoot-through problems associated with voltage source inverters, easing the requirement for PWM dead-times. They also provide a common-grounding feature between the grid-neutral and the negative-terminal of the PV panel, successfully suppressing the PV leakage current. In addition, they provide reactive power support. A simple input boost inductor based buck-boost inverter is proposed with a wide gain range; other variants are also proposed based on switched inductor, quadratic boost, and switched coupled-inductor, achieving higher boost voltage inversions with smaller values of duty ratio. Detailed circuit operations are presented based on proposed modulation strategies. Design guidelines/requirements of components and their comparisons are provided for all of the proposed inverters. The theoretical analysis and performance characteristics of all four topologies are experimentally validated using 400 VA laboratory prototype inverters.