Performance Evaluation of a GaN Flying Capacitor Multilevel Inverter for Industrial Applications

Abstract:
Standard industrial grid connected inverters including their corresponding EMI filter have power densities of only one liter per kilowatt. This application, known as active front end, is typically based on a two-level topology using Si-IGBTs and Si-Diodes and therefore has a limited switching frequency below 10 kHz. It is possible to decrease the filter effort by reducing the voltage-time related area of the switching events. Recent investigations in this area are mainly focused on two-level SiC or three-level Si topologies. With these methods the voltage-time related area is typically reduced by a maximum factor of ten. The volume of the resulting inverters is reduced but is still dominated by the EMI filter. In contrast there are some investigations focused on the flying capacitor multilevel topology in combination with GaN switches. The major part of these publications is focused on motor applications and the presented inverters reach power densities of more than ten kilowatts per liter. In contrast this project is focused on such a multilevel GaN approach for a grid connected 16 kW industrial application. Based on a theoretical optimization an 800 kHz inverter with nine voltage levels is a good compromise between efficiency and power density. This target design reduces the voltage-time related area by a factor of 800 and therefore shrinks the filter effort tremendously. The prototype for this design is presented in this paper and compared to a grid connected standard two-level silicon based inverter.