DC Bus Voltage Balancing in Three-Phase Multilevel T-Type Inverter

While the Neutral Point Clamped (NPC) converter, Flying Capacitor (FC) converter, and Cascaded H-Bridge (CHB) converter represent classical multilevel topologies, these topologies possess certain disadvantages that limit their applicability in certain contexts. NPC topology encounters difficulties in capacitor voltage balancing, particularly when the number of levels is high, the increasing number of clamping diodes complicates the voltage balance algorithm.
T-type inverters present a superior efficiency compared to their NPC counterpart, and the observed efficiency enhancement in T-type inverters can be attributed to their reduced conduction and switching losses. Furthermore, a key advantage of T-type inverters over NPC topologies lies in the elimination of clamping diodes, which are traditionally necessary for maintaining the neutral point potential at the negative or positive DC bus voltages. An active bidirectional switching device is utilized in T-type inverters to achieve voltage clamping. This device interfaces the midpoint of each phase leg with the common node of the series-stacked DC-link capacitors. Nevertheless, T-type inverters, much like NPC converters, confront the challenge of maintaining balanced voltages among the series-connected DC-link capacitor. In this paper, as a contribution, a new technique for capacitor balancing applied to three level T-type inverter based on redundant vectors of space vector modulation is presented and studied.