Design And Performance Analysis of Grid Connected Transformerless Photovoltaic Power System

Abstract

Transformerless photovoltaic (PV) inverters are becoming increasingly popular newlinecompared to transformer-based inverters. The transformerless inverters are more newlineefficient, less bulky and cost-effective. But the system faces the problem of leakage newlinecurrent on account of the elimination of isolation transformers. The leakage current is newlinemainly caused by variations in common mode voltage (VCM). Thus, the problem needs newlineto be mitigated through the inverter topology itself. The objective of this thesis is to newlinestudy and analyze various H bridge transformerless inverter topologies. newlineA bipolar SPWM inverter has lower efficiency than a unipolar SPWM inverter due to newlinehigher switching losses and core losses. The advantages of unipolar modulation have newlinemade it the preferred method over bipolar modulation. Unipolar SPWM control of fullbridge inverters has an attractive feature. However, this leads to higher leakage currents newlinebecause their CM voltage variation. Since unipolar modulation with H4 has limitations, newlinethe voltage swing rate of PV inverters must be reduced by developing new topologies. newlineThe H5 inverter significantly reduces the leakage current by checking the variation of newlinecommon mode voltages. The topology uses only one extra switch apart from the newlineconventional full bridge and is simple to design. To reduce the leakage current H5 newlineinverter topology has been designed which works on the basis of decoupling. The main newlineparameters for analysis are efficiency, leakage current, common mode voltage and their newlinevariation with load. H4 and H5 topology has been simulated and results has compared. newlineThe H5 topology has been found to be effective in suppressing the leakage current to a newlinefairly acceptable magnitude. In order to verify the topology, simulation results are newlineprovided. newline