压接型高压IGBT门极驱动信号演化规律及失效形式研究

Study on Evolution and Failure Mode of Gate Drive Signals of High Voltage Press⁃pack IGBT

压接型高压IGBT是柔性直流输电用模块化多电平换流器(modular multilevel converter,MMC)中的核心器件,其在长期运行中逐渐发生热老化并最终失效,影响着MMC的运行性能。利用压接型高压IGBT的门极驱动信号演化规律监测器件状态对于是实现MMC子模块状态监测的重要手段。文中首先搭建了压接型IGBT功率循环试验平台,并在功率循环试验过程中定期测试器件门极驱动信号波形。结果表明随着老化循环次数的增加,压接型IGBT门极驱动电压上升沿米勒平台时间长度增大,门极驱动电流下降沿凹槽位置滞后。其次,对热老化失效以后的压接型IGBT芯片表面进行观测,发现芯片发射极门极氧化层附件出现裂纹,这一热老化失效形式是门极驱动信号变化的主要原因。最后,根据压接型IGBT内部多物理场耦合关系建立了有限元仿真模型,计算结果表明热应力在附加金属层与下钼层接触界面的边缘区域数值较大,在长期交变的应力疲劳后造成门极氧化层裂纹萌发,逐渐导致门极失效。文中研究结果说明了利用压接型高压IGBT门极驱动信号演化规律在线监测其门极老化状态具有一定意义。

Press⁃pack high voltage IGBT(PPIs)is the core element of modular multilevel converter(MMC)for volt⁃age sourced converter⁃high voltage direct current(VSC⁃HVDC)transmission systems.Its gradual thermal aging and resulting failure during the long term operation affects operation performance of MMC.Utilizing the evolution rule of gate drive signals of PPIs to monitor condition of the elements is the important means to achieve condition monitoring of MMC sub⁃model.Firstly,a power cycling test platform for PPIs is set up to measure periodically the gate drive sig⁃nal waveform during power cycling test period.The results show that with the increase of aging cycling number,the length of the Miller Plateau of the PPIs gate voltage increases and the gate drive current drops and lags along the groove position.Then,it is found after the microscopic observation of the thermal aged and failed chip surface of PPIs that the gate⁃oxidization layer accessories cracks occur on surface of chip emitter side.This thermal aging fail⁃ure mode is the main reason of variation of the gate drive signal.Finally,based on the fully coupled multi⁃physical fields relationship inside PPIs,a finite element model of PPI is set up to calculate the temperature and pressure distri⁃bution of chip emitter surface.The calculation result shows that the thermal stress on the boundary area between addi⁃tional metal layer and the underlying molybdenum layer is lager which,after a long period of alternating stress fa⁃tigue,causes crack germination of the gate⁃oxide layer and gradually leads to gate failure.The research result in this paper shows it is of certain significance to use the evolution rule of gate drive signals of PPI for the on⁃line monitoring of gate deterioration condition of PPIs.