A single source fed three level voltage boost NPC inverter with reduced LC count

Abstract

Single stage boost multilevel neutral point clamped (NPC) Z-Source inverter are becoming prominent for better power quality in low power and medium power applications. The conventional multilevel NPC Z-Source inverter uses two equal DC sources or a split DC source as well as two inductors, two capacitors and two diodes in the intermediate network. However, the source current is discontinuous in NPC Z-Source inverter (ZSI) which is not desirable in some of the applications like fuels cell, UPS system, hybrid electric vehicle etc. Though source current is continuous in multilevel quasi Z-source inverter (q-ZSI), but it uses more number of high power passive reactive elements (inductors and capacitors) which increases the system size, weight and cost. In this paper a three level voltage boost NPC inverter is proposed, which can boost the input DC voltage and give required three level AC output in a single stage. It uses less number of high power passive elements (one inductor and two capacitors), four diodes and two active switches in the intermediate network at the same time retains all the advantages of conventional three level NPC ZSI/q-ZSI. As a result, system size, weight and cost are reduced. Along with the above advantages, proposed inverter requires a single DC source and the source current is continuous in nature. The steady state mode of operation of the proposed inverter is discussed and voltage gain function is derived. The PWM technique for the inverter is also discussed. The simulation and experimental verification of the inverter has been done using MATLAB Simulink and laboratory prototype respectively.