Multilevel open-ended transformer based grid feeding inverter for solar photovoltaic application

Demand for high power direct grid feeding solar photovoltaic (PV) inverters in increasing. To reduce stress on semiconductor devices and harmonic distortion of current waveform, multilevel topology based solar inverters are suggested in literature. Use of Neural Point Clamped (NPC) topology is limited due to complex layout of switches and diodes as compared to 2-level Voltage Source Converter (VSC). Moreover, both NPC and VSC offer only one MPPT tracker for each inverter. Therefore, these inverters may not be effective in extracting maximum power from large PV array under partial shading condition. To address these limitations, a 3-level solar inverter integrating two 2-Level VSCs, supplying real power to the grid is proposed in this paper. Simple layout of the switches and two MPPT trackers are the attractive features of the proposed topology over the 3-level NPC based solar inverter. Mathematical model of the system is derived based on which a controller for the scheme is designed. Effect of partially shaded PV array on current harmonic distortion is analyzed. Effectiveness of the scheme is verified through detailed simulation study.