Derivation, Analysis, and Implementation of a Boost-Buck Converter-Based High-Efficiency PV Inverter

In this paper, a single-phase grid-connected transformerless photovoltaic inverter for residential application is presented. The inverter is derived from a boost cascaded with a buck converter along with a line frequency unfolding circuit. Due to its novel operating modes, high efficiency can be achieved because there is only one switch operating at high frequency at a time, and the converter allows the use of power MOSFET and ultrafast reverse recovery diode. It also features a robust structure because the phase leg does not have a shoot-through issue. This paper begins with theoretical analysis and modeling of this boost-buck converter-based inverter. And the model indicates that small boost inductance will lead to an increase in the resonant pole frequency and a decrease in the peak of Q, which results in easier control and greater stability. Thus, interleaved multiple phases structure is proposed to have small equivalent inductance; meanwhile, the ripple can be decreased, and the inductor size can be reduced as well. A two-phase interleaved inverter is then designed accordingly. Finally, the simulation and experiment results are shown to verify the concept and the tested efficiency under 1-kW power condition is up to 98.5%.