Design and implementation of a power transistor temperature measurement circuit for a multilevel active-clamped power converter

Abstract

Semiconductor power switches are largely considered the most fragile components in power electronic converters. In order to increase the reliability of power devices, it is important to avoid high junction temperatures and high junction temperature fluctuations, which are basically caused by conduction and switching losses in the devices. The purpose of the thesis is to find and implement a robust method to sense the junction temperature of a power switch and deliver this information to the converter controller. The method will be implemented using a circuit that has to be small, cheap and with low-power consumption, since the circuit will be fed by the same power supply used by the gate-driver circuit of the power device. This method is designed to be applied into the multilevel active-clamped converter. One of the main advantages of this topology is its degree of freedom to select the power switch that concentrates the switching losses in the switching-state transitions. By sensing the switches temperatures, it will be possible to always select the coolest transistor to take the switching losses. This will enable a better distribution of the temperature and a lower cost of the cooling system. In addition to this, an improved reliability of the system can be achieved.