Design and Analysis of Transformerless Grid-Tie Buck-Boost Photovoltaic Inverter with Immittance Conversion Topology

Abstract

This article introduces the design and analysis of a single-phase single-stage transformer-less grid-tie buck-boost photovoltaic inverter topology for domestic purposes. Functionally, this new inverter can adjust to a wide range of photovoltaic dc variations, higher or lower dc voltages compared to utility line voltage, and in the meantime track the maximum amount of solar energy all in one single power stage. For switching of inverter power circuit, a combination of sinusoidal pulse width modulation (SPWM) and square wave signal under grid synchronization condition are used. Moreover, to control SPWM duty cycle and to regulate the inverter’s instantaneous ac output voltage, a closed-loop SPWM control technique is used to stabilize the output as fast as possible. Besides, we also employed immittance conversion circuit topology in the inverter output terminal instead of conventional LC filter. The design and analysis of working principles of the inverter control circuit and grid synchronization methods are described in details. This paper mainly focuses on the analysis of working principles, computer simulation of the operation and design consideration of the inverter for grid-connected applications. The effectiveness of the proposed system is clarified through the following mathematical modeling and simulations.

Keywords

• Single-Stage; SPWM; Square Wave; Buck-Boost Converter; Power Electronics; THD; Grid-Tie Inverter (GTI).