Energy Efficiency of an Electric Vehicle Propulsion Inverter Using Various Semiconductor Technologies

In this Licentiate thesis, various solutions to improve the efficiency in the electrical vehicle drive drive line such as in the propulsion inverter and in the electric machine, are proposed and their benefits are quantified from an energy efficiency point of view. The efficiency analysis is based on modeling of a power electronics inverter, an electric machine and a battery in various drive cycles of an electric vehicle. A solution to improve the efficiency in the electric machine is proposed. A loss minimizing optimized current vector control is suggested for a PMSM which minimizes the total machine losses. The solution has for the investigated electric machine up to 8% efficiency improvement or 1.5% improvement in average efficiency of various drive cycles such as ECE, EUDC and US06. Several solutions are studied for the propulsion inverter. It is shown that by replacing the ordinary silicon pn freewheeling diodes in the propulsion inverter with SiC diodes, an average efficiency improvement of about 0.5 percent can be expected in various drive cycles. Furthermore by replacing the Silicon IGBTs in the inverter with SiC MOSFETs, the drive cycle efficiency in various drive cycles can be increased between 4 to 6 percents. Finally a controllable dc-link voltage for the propulsion inverter is investigated in order to qualify the energy efficiency gain for the inverter and the motor. Their drive cycle energy efficiency improvement is 0.5 to 1 percent when using a SiC based inverter and 4 to 6 percents for an IGBT based inverter.