Investigation of a high power three-level quasi-resonant DC-link voltage source inverter

The paper investigates the feasibility of a quasi-resonant DC-link soft switching principle for voltage source inverters (VSI) in the megawatt power range. An evaluation of a three-level quasi-resonant DC-Link VSI (3L-QRDCLVSI) featuring IGCTs and a comparison to a commercially available three-level IGCT-VSI is presented. Extensive loss measurements of IGCTs under hard and soft switching conditions are the basis for the design and the comparison of the inverters. Beside converter losses other important aspects like control, protection and reliability are addressed.