Estimation and control of power electronic device temperature during operation with variable conducting current

Frequent variations in device power loss cause corresponding changes in operating temperature, which may adversely affect device reliability. A method for reducing the device temperature variations is introduced. A simplified third-order thermal model of the device is evaluated in real-time to estimate the instantaneous device temperature. The estimated temperature is used in a temperature control loop to reduce temperature variations by adjusting the device switching frequency. In this way, changes in device conduction loss are counteracted by varying the switching losses, so that the overall losses are substantially constant. The principle is applied to a MOSFET switching a dc load current at random intervals.