Determination and comparison of losses of single phase multi-level inverters with symmetric supply

This paper compares different topologies of three-level voltage-source inverters for industrial and household AC-consumers with approximately 2 kW of nominal power. Due to the specific requirements on this application, the inverter has to operate from a symmetrical DC-link and supplies a single-ended load by a half-bridge topology instead of the conventional full bridge configuration. To increase the quality of the output voltage and to minimize the size of the output filter, multi-level topologies are best suited for this application. This paper focuses on the losses of the semiconductors of different three-level topologies. Analytical methods for the calculation of conduction and switching losses are used to compare the topologies. To confirm the calculated results, the two most promising topologies have been set up in a laboratory environment and tested under variations of load and power-factor. It is be shown that the hard-switching IGBT-NPC-inverter topology gives the best performance in applications which are mostly operated in the range of 80% to 95% of their nominal power with a resistive to inductive load.