Design of a Novel SiC MOSFET Structure for EV Inverter Efficiency Improvement

Young-Kyun Jung,Jong-Seok Lee,Taewon Lim

doi:10.3390/wevj7020206

Abstract

Inverters for electric vehicle motor drive systems are essential in converting the battery's direct current into alternating current. Si(Silicon) IGBT that is commonly used in inverter modules have large Vce,sat and turn-off time due to p+ drain and tail current. Therefore, inverter modules consist of Si IGBT with relatively low efficiency. If we can use MOSFETs instead of IGBT in inverter modules, it is possible to achieve high efficiency because of short turn-off time and high operating frequency. Yet also has a problem; Si MOSFETs has large on-resistance compared to Si IGBTs. In this study, SiC(Silicon Carbide) was used to make MOSFETs instead of Si. Futhermore, an accumulation channel concept is adapted to a SiC trench MOSFET, namely Trench ACCUFET. Compared with conventional SiC trench MOSFETs, the novel SiC trench ACCUFET structure has not only lower on-resistance but also high breakdown voltage as shown by the simulation results. We fabricated the Trench ACCUFET for verification, and described improvements that is to be made.

Highlights

EVs(Electric Vehicles) must be available to travel long distances with the same battery capacity in terms of battery cell efficiency
We proposed a new structure of a SiC trench MOSFET(or trench ACCUFET) with verified simulation results
We proposed a SiC trench ACCUFET structure that has lower on-resistance and higher breakdown voltage compared to conventional SiC trench MOSFETs

Summary

Introduction

EVs(Electric Vehicles) must be available to travel long distances with the same battery capacity in terms of battery cell efficiency. The inverter used to drive the motor of EVs should have good power conversion efficiency. Breakdown voltage increased by 20% and on-resistance decreased by 23% , compared with a conventional SiC trench MOSFETs. we fabricated a trench ACCUFET in order to verify the results and effects. In Electric Power Train of the EV, the driving force utilizes a motor instead of an internal combustion engine. Considering the torque characteristics, the speed required for the vehicle, and the deceleration characteristics of EV, it is necessary to control the high-speed of the motor until 12,000 rpm. This range is 4 times more than that of the industrial usage. To prove the advantages of our SiC trench ACCUFET, a prototype was manufactured at the Fraunhofer Institute, Germany

Simulation results

Process flow

Fabricated device results

Findings

CONCLUSION