FUNDAMENTALS OF A MULTI-PHASE, NEUTRAL-POINT CLAMPED MULTILEVEL INVERTER

Abstract

The conventional five-level diode-clamped inverter suffers from the problem of many active power switches when extended to multiphase system. As a consequence, increasing number of gate drive circuits are required; resulting in complex system circuitry. This paper presents the fundamentals of a multiphase, neutral point clamped multilevel inverter configuration capable of reducing the number of active power switches in the conventional topology for multiphase system. The proposed multilevel inverter configuration generates five line-to-line voltage levels for multiphase systems. From the generalized model, an exemplary 5-phase, 5-level line-line NPC inverter supplying an RL load is considered. The operational and modulation principles and the switching patterns are outlined. The THD, as a performance index, of the line voltage output waveform of the proposed 5-phase, 5-level line-line NPC inverter is similar to that of the corresponding well-known conventional 5-phase, NPC diode-clamped inverter. The proposed inverter achieves this with fewer power circuit components and simplicity. The validity of the proposed multilevel inverter is verified through simulations and experimental results.