A new delta inverter system for grid integration of large scale photovoltaic power plants

Abstract

This paper presents a new grid-connected delta inverter system (DIS) for large scale photovoltaic (PV) power systems. The delta inverter achieves DC to three phase AC inversion by using only three power semiconductor devices instead of six devices as in a conventional full bridge three phase inverter. This reduction in the number of switching devices contributes to higher power density for PV energy conversion systems and potentially, an increase in reliability and lifetime. Two configurations of the proposed DIS are discussed in the paper: (a) A large scale PV field grouped into three DC voltage blocks, each block connected to a front end MPPT boost converter which is connected to a 3-switch DIS interfaced to the utility-grid; (b) PV field connected to a flyback converter with high frequency isolation, followed by a DIS interfaced to utility grid. Advanced pulse width modulation (PWM) techniques are investigated for DIS for operation under unbalanced condition. A design example and simulation results of a 30 kW DIS based PV plant are presented to explore the feasibility of such a system. Experimental results on a scaled down laboratory delta inverter system are shown to demonstrate the operation of this topology.