On the loading of power modules in a three phase voltage source converter

The loading of free wheel diodes (FWD) and IGBTs in the power modules of a voltage source power converter (VSC) are investigated. In converter duty, the FWD are utilized more then the IGBTs. Presently, most FWD in power modules are optimized for inverter duty. This practice tends to undersize the FWD from a converter viewpoint. This design philosophy is examined in the paper. For this purpose, the original dynamic thermal model of IGBTs and FWD were developed. Model parameters were identified from the manufacturers' catalogue data. A mathematical model of the entire VSC was developed to compute current, voltage, power and thermal conditions for the power module and other components in converter operation.