Research On Characteristic And Voltage-sharing Control Of Series-connected IGBTs

The insulated gate bipolar transistors(IGBTs),with good overall performance in the high-voltage applications,have become the most widely used power devices.However,it is difficult for single IGBT to meet the high-voltage requirements due to the manufacture technology limitation.The direct series connection of multiple IGBTs is one of the effective approaches to realize high voltage power conversion,but the static and dynamic voltage sharing is the core issue to ensure stable operation of the IGBTs.Based on the analysis of internal structure and working principle of IGBT,the switch process of IGBT can be divided into different stages.A mathematical simplification Hefner model,is introduced to simplify the understanding of IGBTs.This model theory helps to analyze the model parameters and the external characteristics of each stage in turn-off process detailedly.And the physical relationship between the external characteristics and the model parameters is established.A set of parameter extraction scheme based on switch characteristic test is proposed.The accuracy and feasibility of the parameter extraction scheme are verified by comparing the simulation results with the experimental results.For the series IGBTs dynamic process,the causes of voltage difference during turn-on and turn-off process are analyzed respectively.The influence mechanism of the internal and external parameters is given based on the mathematical model theory.The simulation analysis and experimental tests verify the analysis of the effect of each parameter.It is found experimentally that proper driving delay setting can counteract the influence of other parameters in the series process,which provides the basis for the proposal of driving delay adjustment voltage sharing control strategy.With the positive correlation between the clamp current of the traditional zener active clamp circuit and the IGBT voltage spike,the drive delay adjustment strategy is proposed.And the square proportional regulation scheme is proposed through the fitting curve between the working time of the clamp circuit and the driving delay time.The effects of the fixed step,variable step,proportional and square proportional adjustment of the drive edge control are compared experimentally,which shows that the square proportional regulation scheme can get better rapidity and stability.