A novel control method to improve the reliability of traction inverters for permanent magnet synchronous machines

In automotive applications system reliability is of major importance. The Voltage Source Inverter (VSI) of a traction system is a reliability and lifetime limiting factor due to the limited temperature cycle capability of its switching devices, commonly IGBT-modules. Temperature swings caused by varying load conditions on the motor cause mechanical stress in the switching modules due to change in power dissipation. This paper presents a novel control method, which achieves a reduction of temperature swing during low load conditions by increasing the conduction losses of the switching devices. A temperature controller increases the motor current without affecting the mechanical output power of the supplied motor. This is possible, as a specific motor torque and power can be achieved with different current values as long as certain lower and upper current limits are observed which are defined by system parameters and operation conditions.