Abstract

Today, motor inverters in the kW domain typically are implemented using silicon (Si) based insulated gate bipolar transistors (Si-IGBT) operating in pulse width modulation (PWM) mode at switching frequencies up to 20 kHz. During the past few years, however, wide-bandgap switching devices like GaN- and SiC-MOSFETs have been significantly improved, especially concerning voltage capability of GaN devices. Due to the low switching- and also low on-state losses of GaN MOSFETs in comparison to Si-IGBTs, motor inverters with rather high switching frequencies but also high efficiency rates can be achieved. However, the occurring high switching speed of the transistors create some crucial issues for motor applications. To avoid and reduce negative effects of high-speed switching, the GaN inverter has to be extended by a filter system, which suppresses all switching noise at the inverter's output such that motor and cabling are fed by "sinusoidal-like" voltages. A two-stage LC output filter is used to achieve sufficient attenuation of the switching frequency harmonics. To obtain higher inverter efficiencies, an active damping concept of the LC-filter by feedback of the capacitor filter currents is applied instead of dissipative damping paths. However, inverter voltage limitations and nonlinearities of passive filter elements have negative influence on the chosen active damping scheme. The paper presents a simple control adaption to reduce the occurring effects and guarantee a stable system behavior. Therefore, a mathematical model is implemented, which represents the physical properties of the filter and the motor as a load. In addition, the influence of a dead time, according to data logging, in the capacitor current measurement path on the model stability is also briefly examined.