Research Of Series Connection Of IGBTs With Voltage Balancing

The development of power electronics requires higher voltage power electronic devices. IGBT has become a very broadly used device in application of power electronic because of its good switching performance. However, the maximum rated voltage of IGBT is 6.5 kV. The series connection of IGBTs not only can obtain higher rated voltage, but also obtain better switching performance under the same voltage level. But the voltage on series connection of IGBTs is easy to be imbalanced, and causes overvoltage on the devices. The imbalanced voltage problem is urgent to be solved.This paper expounds the internal mechanism of IGBT, and builds the physical simulation model in PSPICE software. The model built in this paper is compared with SPICE library model in same simulation circuit, and simulation results verify validity of physical simulation model built in this paper.The dynamic process of IGBT in stages of switching on period and switching off period is analyzed in this paper, the possible reasons for the series voltage imbalance in the switching periods is given. The existing voltage balancing schemes is summarized. The advantages and disadvantages of two typical method, which is active clamping method and magnetic core synchronization method, is researched, A hybrid voltage balancing method which combine above two methods is proposed in this paper, the hybrid method applies effective control over the whole switching dynamics.Based on theoretical analysis and simulation by the PSPICE software, the hybrid control of series IGBTs is researched under different possible conditions which could cause voltage imbalance. A high voltage Boost DC/DC converter with series connected IGBTs was built. The experimental results fit the theoretical analysis and simulation well. The experimental results showed good performance of the hybrid method in voltage balancing, against several factors which may cause unbalance in series connected IGBTs. The feasibility of the hybrid method in balancing the voltage of 4 series connected IGBTs was also verified by the experimental results.