Single-Phase Five-level Transformerless Inverter for Multi-String Photovoltaic Applications

In this paper a novel single-phase two-stage five-level asymmetrical filter inductor based transformerless inverter is proposed for the multi-string photovoltaic (PV) applications. The multi-output boost converter is developed with resonant soft-switching circuit to obtain either zero current switching (ZCS) or zero voltage switching (ZVS) during turn-on and turn-off of the both main and auxiliary switches. The six switch asymmetrical filter inductor based five-level inverter eliminates the high-frequency oscillations in the common mode voltage (CMV). Consequently, the flow of leakage current magnitude from the grid to PV panels is reduced significantly without the use of an isolation transformer. Moreover, the improved modulation scheme enhances the inverter operation in all the operating power factor conditions of the grid. Further, the integration of the soft-switched multi-output boost converter and five-level inverter at reduced power losses increases the overall efficiency and reliability of the multi-string PV systems. Simulation studies are carried-out in the PSIM and MATLAB platforms to validate operation of the proposed concept.