A Novel Neutral-Point-Clamped Half-Bridge Eleven-level Inverter With High DC Voltage Utilization Ratio and Fewer Switches

Multilevel voltage source inverters are superior solutions for medium-voltage (MV) and high power applications, which can meet the requirements of high power density, efficiency and power quality. This paper presents a novel Neutral-Point-Clamped Half-Bridge (NPC-HB) eleven-level inverter topology which is composed of two power switches at fundamental frequency connected in series with the positive and negative poles of the DC voltage source and a seven-level NPC-HB inverter. Only ten switching devices are needed to generate eleven voltage levels, which improves the power density of the inverter system with fewer switches. Besides, the DC voltage utilization ratio of the proposed topology is higher than 1. After the comprehensive analysis of the operation principles of the proposed topology, a proposed compound modulation strategy based on phase-disposition pulse width modulation (PD-PWM) suitable for the eleven-level inverter is described in detail. With the proposed modulation strategy, the violent fluctuation of flying capacitor voltage is solved when the modulation degree is high. Simulation and experimental results verify the validity of the proposed topology and modulation strategy.