The Research On The IGBT Driving Strategy And Simulation

With the constant improvement of IGBT power level, the IGBT driving strategy is faced with new challenges, such as the contradiction between withstand-voltage and switching speed, the conflict between slower turn-on process and earlier detection of short-circuit and the higher turn-off voltage spike caused by the larger rate of decrease of current, and so on. Therefore, it is of vital significance to research on the IGBT driving strategy which can optimize the switching process and enhance the performance of short-circuit protection.In this thesis, the mechanism and characteristics of IGBT are introduced. The Hefner mathematical model is deduced in detail and the turn-off transient model is amended by defining the depletion layer capacitance as a function of time. Based on the conclusions, the IGBT driving and protecting strategies are researched, which include the closed-loop variable gate resistance switching strategy, the dic/dt detecting short-circuit strategy combined with collector-emitter voltage and the soft turn-off strategy based on variable gate voltage. The IGBT model is established in Saber, and the static characteristic test and double pulse test are simulated. The IGBT driving strategy simulation platform is built by using the model and a seris of simulations are carried out. The closed-loop variable, open-loop variable and constant gate resistance switching strategies are simulated and contrasted. The short-circuit detecting strategy simulation is done in different short circuit conditions. The hard turn-off and soft turn-off short-ciucuit protecting strategies are simulated and contrasted under different short-circuit circumstances.The results of the static and dynamic characteristic simulations on the IGBT model are compared with the datasheet and similar simulation result, showing the high accuracy of it. Then, the driving and protecting strategy simulations are carried out based on the model and the superiorities of the strategies proposed in this thesis are indicated by the results. The closed-loop variable gate resistance switching strategy has such advantages, the automatic switching time determination, the faster switching speed and the less power dissipation. Different short circuit conditions could be deteceted comprehensively by dic/dt detecting short circuit strategy combined with collector-emitter voltage, and the detecting time is earlier in large dic/dt situation. With the soft turn-off strategy based on variable gate voltage, the turn-off voltage spike under short circuit is reduced significantly and it is unnecessary to wait until the collector-emitter voltage reachs busbar voltage.