Active Utilization of a Full DC-Link Voltage in Multilevel Converter

Abstract

Multilevel inverter technology has emerged recently as a very important alternative in the area of high-power medium-voltage energy conversion. Multilevel inverter reduces the inductors and filters size, whilst improving the output power quality. However, the main drawback of the multi-level inverter topologies is that they utilizes only ≤ 50% of the input dc-bus voltage, i.e. they require two times the peak of ac output voltage. For example, the nominal input voltage of the NPC, ANPC and Flying Capacitor is 800 V dc . This high dc-link voltage not only requires higher voltage components (both active and passive) but also prompts to use an additional front-end boost dc-dc converter. Considering these aspects, this paper presents a novel technique to extend the input dc-bus voltage utilization in any conventional multilevel inverter from ≤ 50% to ≤ 100%. The novel technique utilizes an additional T-type module (consist of four active switches), which is inserted just before the two dc-link capacitor forming a new grounding point. The novel method not only reduces the input voltage requirement and voltage stress, but also increases the output voltage levels of the inverter. In general, this technique can be implemented to any multilevel inverter. An example of implementation of 5L inverter from the conventional 3-Level T-type inverter is discussed and validated. Measurement results shows that the new Dual T-type inverter has a flat efficiency « 99 % over a wide range of load.