Research On Voltage Balancing Techniques Of Series Connected Insulated Gate Bipolar Transistors

The Insulated Gate Bipolar Transistor(IGBT) has distinct advantages as the powersemiconductor switch. It has fast switching speed, high through-flow capacity, simpledrive and a wide safe operation area, etc. However, due to the low withstand voltagerating of a single IGBT device, its wide range of application in the high voltageoccasions is restricted, especially in the ultra-high voltage and high voltage directcurrent transmission system. Series connection of IGBTs is a direct and effectivesolution. The unbalancing voltage among the series connected IGBTs is a key problemduring static and dynamic transient states, which causes the breakdown of the devicesand series fail. Therefore, it is greatly significant to do research on the voltage balancingtechniques of series connected IGBTs.According to the basic theory of IGBT, the basic structure of the IGBT, theworking principle and the basic characteristics are elaborated in detail. Especially, thedynamic characteristics of the IGBT are carefully analysed. Meanwhile, the commonlyused IGBT drive and protection circuits are briefly described.Secondly, in order to research the mechanism of unbalancing voltage among theseries connected IGBTs, the simulation model for the series connected IGBTs isestablished by Saber software. Voltage distribution among the series connected IGBTswhich is affected by different parameters of the IGBTs, the peripheral circuits, thedistributed capacitors and so on, is discussed emphatically. The relationship betweenchanging parameters and voltage distribution is depicted through adopting themaximum voltage unbalancing rate during switching transient.Thirdly, based on analyzing and summarizing the existing voltage balancingmethods, the technique which minish the slope of collector-emitter voltage for seriesconnected IGBTs, extend the duration of its switching transient, to reduce the maximumvoltage unbalancing rate is a feasible way.Finally, aim to the unbalancing voltage among the series connected IGBTs, the twokinds of improved voltage balancing circuits are presented in this paper, afterresearching the power and gate terminal voltage balancing technology respectively.Then, the slope of collector-emitter voltage changed circuit with energy recovery isproposed based on the power terminal voltage balancing technology. And the activevoltage balancing circuit based on enhancing Miller effect is proposed based on the gate terminal voltage balancing technology. Those circuits can achieve to adjust the slope ofcollector-emitter voltage for series connected IGBTs. So, the good effect for balancingvoltage among the series connected IGBTs is verified by simulation and experiment.