Abstract
One of the emerging research topics in the propulsion drive of the electric vehicles is the improvement in the efficiency of its component parts, namely, the propulsion motor and the associated inverter. This paper is focused on the efficiency of the inverter and analyzes the improvement that follows from the replacement of the silicon (Si) IGBT devices with silicon carbide (SiC) MOSFETs. To this end, the paper starts by deriving the voltage-current solicitations of the inverter over the working torque-speed plane of the propulsion motor. Then, a proper model of the power losses in the inverter over a supply period of the motor is formulated for the two types of device, including the integrated freewheeling diode. By putting together the voltage-current solicitations and the device power losses, the efficiency maps of the Si IGBT and SiC MOSFET inverters are calculated and compared over the torque-speed plane. The results for the Si IGBT inverter are supported by measurements executed on a marketed C-segment compact electric car, while the SiC MOSFET loss model is validated by an on-purpose built test bench. Finally, the overall efficiency of the propulsion drive is calculated by accounting for the motor efficiency. Main outcomes of the paper is a quantitative evaluation of both the improvement in the efficiency achievable with the SiC MOSFETs and the ensuing increase in the electric car range.
Highlights
It is well known that the main drawbacks of today’s electric vehicles (EVs) are the limited range and the long recharging time of the batteries
Putting together the results found above, it can be concluded that the silicon carbide (SiC) MOSFET propulsion drive outperforms the efficiency of the Si IGBT one of a few percent over most of the regions of the torque-speed plane, whereby the exact amount of the improvement, like in any engineering approach, should account for the measurement errors and data tolerances
The paper has explored the improvement in the efficiency of a propulsion inverter for EV, achievable by replacing the Si IGBTs of the propulsion inverter with SiC MOSFETs
Summary
It is well known that the main drawbacks of today’s electric vehicles (EVs) are the limited range and the long recharging time of the batteries. A few papers have investigated the efficiency of SiC MOSFET inverters [12, 13] By expanding their investigation, this paper provides the efficiency map of a SiC MOSFET inverter over the working torque-speed plane of a propulsion motor. This paper provides the efficiency map of a SiC MOSFET inverter over the working torque-speed plane of a propulsion motor For the latter one, a permanent magnet synchronous motor is selected because of its large use in today’s EVs. The same investigation is accomplished for a Si IGBT inverter for comparison purposes. The efficiency is calculated in two steps: by deriving the amplitude of the inverter current-voltage solicitations for given values of motor torque and speed and by arranging a suitable model for the losses in Si IGBTs, SiC MOSFETs, and freewheeling diodes. Appendix describes the experimental activities performed to validate the loss model of the SiC MOSFETs
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