一种用于V形钳位多电平变换器的IGBT吸收电路方案

Research on an IGBT Snubber Circuit for the V-clamp Multilevel Converter

只有公共直流侧电容的V形钳位多电平变换器(VMC)在中压、大功率电能变换的场合具备良好的应用价值。但当VMC电平数较高时,其换流回路电感不可避免地增大,使IGBT开关器件的关断过电压问题凸显。为此,该文提出一种简单的VMC吸收电路方案。依据VMC的运行原理,将其开关器件区分为主开关器件和辅助开关器件。主开关器件动作并切换电流通路,在每一对互补的主开关器件两端添加吸收电容(构成类似半桥开关能量缓冲单元),以抑制其关断过电压。而主开关器件相对应的辅助开关器件则先开通、后关断,仅提供静态电压支撑的功能,因此无需吸收电路保护。该文以七电平VMC为例,对所提的吸收电路方案进行了分析和研究。实验结果表明,所提的VMC吸收电路方案能够显著抑制开关器件的关断电压尖峰。并且,该方案仅需少量吸收电容与主开关一起构成类似半桥开关能量缓冲单元的形式即可实现所有开关器件的关断过电压保护,其成本低、可靠性高,具有良好的工程实用性。

V-clamp multilevel converter(VMC)with the energy buffer capacitor only in common DC bank is suitable for the medium-voltage and high-power applications.However,stray inductance in the current transition loop of VMC may result in the turn-off over-voltage of the IGBT.To address this problem,this paper proposes a simple and practical snubber for VMC.Based on the operation modes of VMC,the switches are classified into main switches and auxiliary switches.The main switch operates and switches the current path,and a snubber capacitor is added across each pair of complementary main switches(i.e.half-bridge switching buffer alike unit)to suppress the turn-off transient over-voltage.The auxiliary switch is turned on first and then turned off after the switching time of the corresponding main switch,and only provides the static blocking voltage and does not need dynamic over-voltage protection.A seven-level VMC is taken as an example to verify this strategy.The experimental results show that the proposed snubber circuit can effectively reduce the turn-off transient voltage of the IGBT in VMC,and only needs a small amount of snubber capacitors for main switches to form half-bridge switching buffer alike units.It has low cost,high reliability and good engineering practicability.