A novel test method for minimising energy costs in IGBT power cycling studies

摘要

Insulated Gate Bipolar Transistors (IGBTs) are popular power electronicudswitching devices with several advantages. However, they have been known toudfail in the field when subjected to significant variations in power dissipation –udknown as power cycling. In the work presented here, a novel alternating-currentud(AC) power cycling test method for IGBTs together with their free-wheelinguddiodes is proposed and verified.udA review of previous work revealed that the parameter that most affects IGBTudlifetime under power cycling conditions is the variation in its junction-caseudtemperature difference. Through simulation, the behaviour of audconventional single phase inverter (H-bridge) using simple pulse widthudmodulation (PWM) control was quantified, and the effect of switching frequencyudand load power factor was studied.udResults of the simulations and literature review were used to develop designudcriteria for a new AC test circuit. The new AC test circuit (a modified version ofudthe conventional H-bridge) was then designed and its performance compared toudthe criteria and to the simulation results of the conventional circuit. The circuitudwas then built and its performance was validated. The circuit complied with theudperformance criteria, in particular the desired variation in 7jc, to an adequateuddegree of accuracy.udThe proposed test circuit is novel for several reasons. The stresses on devices usedudin a conventional H-bridge using a high power factor inductive load areudreproduced using a low power factor inductive load, considerably reducing theudenergy cost of running such a test. IGBT switching losses are not activelyudreduced, as is normal practice, but instead are actively increased to generate theudrequired losses. Free-wheeling diodes are also tested, but do not have significant udswitching losses, as the nature of the test circuit dictates that these be transferredudto the IGBTs.udThe main drawback of the proposed test circuit is that a larger number of devicesudare needed; however, this tradeoff is necessary to obtain the energy cost savingsudprovided by this circuit.