Performance Comparison of Conventional VSI and H5 Transformerless Inverters in a Utility-Scale Grid-Connected Solar PV System

Abstract

Transformerless grid connected photovoltaic (PV) inverters are very popular because they are highly efficient, they occupy less space and they are relatively cheaper. Nevertheless, they have serious limitations of common-mode (CM) voltage variations, leakage current, and deterioration of power quality of the grid. In order to solve these problems, more complex inverter topologies with no transformer like the H5 inverter have been introduced. However, there is a lack of extensive comparative studies of the medium-power PV systems operating on the same operating conditions.The paper includes a comparative performance study of two inverter designs, a traditional three-phase two-level voltage source inverter (VSI) and an H5 transformerless inverter in a 175 kW grid-connected PV system. A hybrid modelling and control system is created with irradiance and temperature variations that are realistic. The inverter performances are critically checked according to switching features, common-mode voltage, ground leakage current, grid current quality, harmonic spectrum, and instantaneous active power transfer.Simulation results in time and frequency domains have shown the conventional VSI to have large changes in CM voltages and large leakage current. Conversely, the H5 topology is an excellent system to suppress leakage current through the decoupling of the PV array during the freewheeling periods and enhances the overall quality of the power. Moreover, the H5 inverter injects a sinusoidal grid current of high quality with under IEEE519 harmonic levels and performs better than the usual VSI in the medium-power transformerless PV applications.