An improved quasi Z-source based H5 inverter with low leakage current for photovoltaic applications

Abstract

Grid-connected Single-Stage Boost Inverters (SSBI) are extensively being researched in the area of photovoltaic energy conversion systems. Owing to their single-stage boosting capability, this class of power converters results in higher efficiency and reliability. This power circuit configuration is constituted by two mutually dependent sub-converters, in that a front-end quasi-Z-source (qZS) part is integrated to a back-end multilevel inverter (MLI). The MLI provides the shoot through state to the qZS, while the qZS provides the pulsating DC input to the MLI. In general, solar photovoltaic inverters suffer from the disadvantage of leak age current that flows from solar panels to the grid/load. This paper introduces a dual quasi-Z-source based multilevel inverter, which achieves the following bene fits: (a) five-level output voltage, (b) reactive power capability, (c) shoot-through immunity, (d) continuous input current, and (e) reduced leakage current based on VDE 0126-1-1 standards. In this paper, a modified modulation scheme, which is based on the employment of phase-disposed and level-shifted carrier signals, has been used to reduce the leakage current. To reduce the leakage current fur ther, a passive filter is employed to eliminate high frequency variations across the parasitic capacitance. The working principle of the proposed power converter and the effectiveness of the modulation scheme have been validated with simulation studiesinbothstandaloneandthegrid-connected mode. Finally, the simulation studies are verified through an experimental prototype of 500 W rating.