Capacitor voltage self‐balancing using active DC‐link technique for a single‐phase, five‐level neutral point clamped inverter

Abstract

SummaryThe article proposes a new DC‐link voltage balancing method for a single‐phase, five‐level DC/AC neutral point clamped (NPC) inverter. Nowadays, the NPC converter is a suitable solution for various applications; however, the unequal voltage of the DC‐link capacitors is a significant disadvantage of this topology. In this paper, a simple auxiliary unit is inserted in the DC‐link to enable a self‐balancing capacitor voltage. The auxiliary circuit is composed of two capacitors and four active switching devices. The idea of the proposed method is to construct an active DC‐link bus; thus, the two DC‐link capacitors can be connected in series during the charging process and in parallel during the discharging process. As a result, its capacitance and root mean square (RMS) current are greatly reduced. Unlike other auxiliary circuits, the new method requires no additional storage elements or complex control systems. The operating principle and switching schemes are analyzed. The effectiveness of the introduced method is evaluated experimentally using the balancing circuits under different load conditions and different value of modulation indices.