Part load efficiency improvement of electric vehicle traction inverters

This work deals with resent research activities regarding electric drives for automotive applications. Special focus lies on improving the drive's efficiency especially the power electronics inverter. At part load operation, which is most relevant for electric vehicles, considerable potential for efficiency optimization and reduction of power dissipation in the electric drive components exists. Various approaches to improve inverter efficiency are introduced: reducing the switching frequency, changing system parameters such as DC-link voltage and adapting the active chip area. Focusing on the latter method a new approach to changing the active chip area of semiconductor devices (IGBTs) during inverter operation is introduced. In order to analyze this approach a unique prototype has been designed which uses several individually-controlled half-bridges in parallel per phase. When the drive is operated at part load not all half-bridges are required to drive the electric machine current thus deactivating unnecessary IGBTs can lead to an efficiency benefit by reducing switching losses in inactive chips. In order to investigate this method and compare various driving cycles several simulation models are presented to estimate drive resistances, the electric machine and electric as well as thermal behavior of the drive inverter. Using these simulation tools driving cycles are analyzed and the impacts of different optimization approaches are evaluated regarding drive efficiency and inverter life time. In addition to simulating driving cycles experiments using the aforementioned prototype have been conducted and measurement data on inverter efficiency and semiconductor temperature has been obtained.