Junction Temperature Control System to Increase the Lifetime of IGBT-Power-Modules in Synchronous Motor Drives Without Affecting Torque and Speed

Load changes of electrical machines driven by inverters cause temperature swings of the semiconductor devices in IGBT modules of the inverters. These temperature swings lead to mechanical strain in the different material layers of the IGBT-power-modules and limit the numbers of cycles to failure and therefore reduce the lifetime of the IGBTs. This paper presents a temperature control system which is paralleled to the standard torque control system. It aims to reduce the magnitude of temperature swings of the semiconductor devices of IGBT modules caused by load changes of an interior permanent magnet synchronous machine. The principle method is, to increase the temperature of the semiconductor devices of the IGBT-modules by creating higher power losses during low load conditions of the machine without affecting torque and speed. This reduces the magnitude of the load induced temperature swings of the semiconductor devices of IGBT-modules and increases its lifetime at the cost of increased power losses. Three variables have been identified that influence the power losses in inverter modules without necessarily affecting the output power of the permanent synchronous machine. These variables are switching frequency of the inverter, length of the clamping area when a discontinuous modulation is applied and the reactive component of the inverter current. The influence of each variable which regards to the losses in the IGBT-power-modules is explained and the related control methodology is described. The analytic results are verified by experimental results obtained from a test set up.