Low loss Motor Terminal Filter crushing du/dt Limitations

Abstract:
Shielded motor cables are used in many applications for traction purposes. The cables connect the voltage source inverter and the electrical machine. Due to the commonly known reflection phenomenon, explained by the traveling wave theory, the motor terminal input voltage can reach twice the DC-link voltage or in some cases even higher values. The wider implementation of SiC MOSFET with its capability for high switching speed forces the reconsideration of reflection phenomenon for applications that are affected by high voltage stress due to voltage reflection. This paper shows a deep investigation of one method to reduce the machine terminal voltage without restricting the MOSFET voltage slope. A simple RC Filter at the motor terminal reduces, with proper design, the motor terminal voltage to a desired value. In this work several parameters as cable length and different values for the filter elements are varied to point out the optimal filter configuration which is able to limit the terminal voltage to a required maximum. Furthermore, the effect of the filter on the voltage distribution in the stator is examined. The proper implementation of the filter crushes eventual du/dt limitations for the inverter and allows fast switching and therefore enables low switching losses.