Research on Snubber Circuits for Power Electronic Switch in DC Current Breaking

The research on snubber circuits for power electronic switch (PE switch) in DC current breaking is introduced in this paper. During the turn-off of PE switch, the voltage of power electronic devices rises quickly due to the high di/dt and system inductance. MOV is connected in parallel with PE switch to absorb the fault energy and suppress overvoltage. However, the voltage across PE switch would surpass the nominal voltage of MOV because of the stray inductance existed in the loop of PE switch and MOV. J.Magnusson proposed a method without snubber by the use of parallel varistors. By analyzing the transient power shock during turn-off, it is concluded that the method achieves the ability of overvoltage suppression at the sacrifice of current turn-off capability. Thus, snubber circuits are indispensable for PE switch in DC current breaking. Through the analysis on principles of snubber function during turn-off operation, the electrical features and parameter of snubber circuits are obtained and two different snubber circuits suitable for PE switch are specifically introduced. Then, a test platform is set up and experimental comparisons are carried out. The turn-off results show that RC snubber has lower overvoltage peak while bringing stronger switch-off power shock than RCD. The further analysis indicates that RCD is more suitable for turn-off capability promotion and RC has advantages in overvoltage spike suppression.