On line thermal model and thermal management strategy of a three phase voltage source inverter

Abstract

A third order dynamical thermal model suitable for modeling diodes and IGBTs is proposed. The method for deriving model parameters from manufacturers data sheets is derived and verified. Models of the power circuit devices, IGBTs and diodes, together with a heat sink model are combined into a dynamical thermal model of 3-phase inverter bridge. The model, together with thermal management strategy is implemented in a microprocessor. The instantaneous values of junction temperatures of IGBTs and free wheeling diodes (FWDs) are estimated on-line with a one step ahead prediction algorithm. If the temperature on any of the power devices reaches a critical value, the PWM frequency is reduced or the PWM method changed in order to reduce losses. If switching losses are still too high and minimum allowable switching frequency is reached; the thermal model starts to reduce inverter current in order to keep the junction temperature of the hottest device of the power circuit below a critical level. The dynamical model with thermal management strategy becomes most useful at low frequency, i.e. stall speed like operation of the drive with high instantaneous loading on particular devices in the power circuit.