An Optimized Hybrid PWM Strategy for Five Level NPC VSI With Unequal DC-Links in a PV System

This article presents an optimized hybrid pulsewidth modulation (PWM) strategy for five-level neutral point clamped (5L-NPC) inverter with unequal dc-link capacitor voltages fed by differential power processing (DPP)-based photovoltaic (PV) system. The generation of balanced output from the 5L-NPC inverter with the unequal dc-link capacitor voltages becomes necessary in a PV system. The unequal dc-link capacitor voltages cause low order harmonics in inverter output voltage. A hybrid PWM strategy combining the advantages of space-vector PWM (SVPWM) and the nearest level modulation (NLM) methods is proposed to address the issues associated with unequal dc-link capacitor voltages in a five-level NPC inverter. The proposed hybrid PWM is optimized to achieve balanced output voltage with less total harmonic distortion at fundamental frequency. In-depth theoretical analysis of sector identification algorithm and dwell time computation for the proposed optimized hybrid PWM method are described. Simulation and experimental results are illustrated for several combinations of unequal dc-link capacitor voltages to validate the functionality and performance of the proposed optimized hybrid PWM method.