Design of a Transformer-less Grid-Tie Inverter Using Dual-Stage Buck and Boost Converters

Abstract

This paper introduces a topology for transformer-less pure sine wave grid-tie inverter (GTI) for photovoltaic (PV) applications. The proposed GTI employs a dual-stage switch mode boost converter, a dual-stage switch mode buck converter, an H-bridge inverter and a T-LCL immittance conversion circuit. For switching of GTI power circuit, a combination of sinusoidal pulse width modulation (SPWM) and square wave signal under grid synchronization conditions are applied. As the suggested method is entirely transformer-less, it astonishingly reduces Total Harmonic Distortion (THD) which is less than 0.1%, minimizes the size of the inverter and increases inverter efficiency up to 97%. The T-LCL immittance conversion circuit not only reduces the harmonic distortation of inverter output but also provides a nearly constant output current thereby stabilizing the system instanteously. Using the designed values of circuit components, the overall performance of the proposed inverter is simulated by using PSIM software. The simulation results not only show that the proposed inverter eliminates vast harmonics but also prove that it is highly efficient, compact in size and cost effective due to being transformer-less.