A >98% efficient >150 kRPM high-temperature liquid-cooled SiC VFD for hybrid-electric turbochargers

This paper presents a high-efficiency, high-speed variable frequency drive (VFD) used in an electrically-assisted turbocharging application with the goal of reducing turbo lag and extracting electrical energy during vehicle braking and deceleration events. To maximize switching frequency and achieve high-temperature operation, SiC MOSFETs are used in lieu of Si IGBTs or MOSFETs. Furthermore, the VFD is cooled using the existing engine coolant loop, which operates near 105 deg. C. Eliminating the need for an additional 65 deg. C liquid cooling loop, which are typical of electric vehicles, significantly reducing system complexity, volume, and weight and simplifying integration. A digital sliding-mode-observer (SMO) was developed to drive the machine at a ramp rate of over 68 kRPM/sec. A dead-time compensation algorithm based upon adaptive notch filters was used to eliminate low-order current harmonics, which can degrade the sensorless control algorithm's performance. Experimental results are presented confirming the VFD's efficiency, dynamic control performance, low-THD load current, and high-temperature operation. Lastly, using a previously developed electro-thermal model, the VFD is extended to higher voltage (450 Vac) motors for application in future vehicle traction drives. The results show that the presented drive exceeds the Department of Energy's targets for traction drives in 2020.