Research On Dynamic Voltage Balancing Technique Of High-voltage Large-capacity IGBT In Series

IGBT (Insulated Gate Bipolar Transistor) is widely used in the field of HVDC flexible and power drives as a kind of full-controlled electronic devices which has superior performance. However, its utilization is limited in the high and ultrahigh voltage industrial application because of its low withstanding voltage of single device. For solving this problem effectively, the serial use of IGBTs is proposed. There are many factors which will cause voltage unbalance, so researching on the influence factors and the techniques of IGBT series connection has great significance.The key work of this paper includes:the modeling method for high voltage IGBT in Saber software is proposed; influence factors are analyzed in details and the quantitative method of influence degree on the voltage balance in series-connected circuit is posed.First, the application status of high voltage IGBT and the modeling methods of IGBT are summarized, and the properties of voltage balance methods in series-connected circuits are analyzed. Based on the physical structure of IGBT, the operation characteristic and working process of IGBT are described and the main parameters of IGBT which may affect voltage balance are introduced. The requirement of gate driving circuit is also analyzed.Next, the simulation environment and the application scope of Saber software are introduced; the modeling method of high voltage IGBT in Saber is proposed. The parameters selection strategies and validation methods are investigated in details. Characteristics of turn-on and turn-off of IGBT are analyzed based on this behaviour model.Then, the influence factors of unbalanced voltage in the series-connected circuit are studied through simulation on the behavior model of IGBT in the Saber software. The influences can be divided into two main aspects:the the outside circuit parameters which include the un-synchronous of gate drive signals, the stray parameters of gate circuit and the parameters of parallel-connected diode with IGBTs; the inconsistent parameters of IGBT itself which include the capacitance among three poles, the different resistors of gate pole, the stray inductance of the lead wires and so on.Finally, the parameter selection strategy of voltage balance circuit are posed according to the analysis of influence factors in the series-connected circuit. The effectiveness of the selection strategy is validated though simulation results.