Input/Output EMI Filter Design for Three-Phase Ultra-High Speed Motor Drive GaN Inverter Stage

Pairing wide-bandgap (WBG) inverters with high-speed motors results in compact and effi cient motor drives, but requires special attention on electromagnetic interference (EMI) aspects. This paper focuses on electromagnetic compatibility (EMC) of high-speed motor drives, supplied by a DC source. In order to protect the nearby equipment from the EMI noise of the WBG inverter, a fi lter that complies with conducted EMI regulations is placed at the inverter DC input-side. However, there is no clear mandate requiring from inverters to comply with conducted EMI regulations at the AC output-side, where only the motor is placed. For this reason, there is no full consensus whether it is necessary to use an output fi lter, and if so, what type of output fi lter would be suitable, i.e., if differential-mode (DM), common-mode (CM) or both DM/CM output fi lter would fi t best. A full sine-wave output fi lter (FSF) is proposed in this paper, that features both DM and CM attenuation, and capacitors connected to the DC link. Besides the several well established benefi ts of a FSF, such as purely sinusoidal motor currents and the protection of the motor against high du/dt originating from the fast switching of the semiconductor devices, a FSF at the inverter output-side, also reduces the CM EMI emissions at the inverter input-side. Namely, since the inverter housing, the motor housing and the interconnecting shielded cable are all grounded, CM emissions generated at the inverter output-side are directly mapped to the inverter input-side, i.e., there is an input-to-output CM noise interrelation. A FSF reduces the output-side CM EMI emissions and thus mitigates the input-to-output CM noise mutual influence. Two types of FSF (c-FSF and d-FSF) are comparatively evaluated, in terms of volume, losses and EMI performance. The theoretical consideration are tested within the context of a high-speed 280 krpm, 1 kW motor drive, with 80 V DC supply. The experimental results validate the good performance of the proposed filter concept.