The Effect of Modulation Index in THD of Transformer less Inverter

Abstract

Due to the fast increase of photovoltaic (PV) adoption and utilization, their efficiency and power quality become of great importance. The grid connected inverter is a basic part in grid tied solar system. The inverter design has to keep the total harmonic distortion (THD) under permissible and tolerable limits. In this work, several techniques have been suggested and employed to mitigate the effects of the THD in the inverter output. These techniques are based on using both the sinusoidal pulse width modulation (SPWM) while varying the amplitude modulation index (Ma) for controlling THD. The full bridge and H5 transformerless topologies has been simulated at different modulation index Ma using MATLAB Simulink. The simulation shows that H5 topology has a lower THD than the unipolar inverter. Also, the results verified that the best performance of the two topologies occurs at Ma = 1.02.