Flyback-type di/dt snubber for 10kV IGCT in MV wind turbines

Converters employing IGCTs usually require di/dt snubber and over voltage protection (OVP) circuit for the protection of IGCTs. In these IGCT-based converters, loss of conventional di/dt snubber and OVP clamp circuit is relatively high. To reduce this loss of conventional di/dt snubber and OVP clamp circuit, this paper proposes a flyback-type di/dt snubber for IGCT-based converters. This flyback-type di/dt snubber simply consists of a flyback-type transformer and a clamp diode. The proposed circuit reduces loss and simplifies conventional di/dt snubber by adopting the flyback-type transformer. The loss analysis of conventional di/dt snubber and OVP clamp circuit is performed for the neutral point clamped (NPC) 3-level back-to-back type voltage source converter (VSC) supplied from grid voltage of 6.9kV. At maximum, the proposed flyback-type di/dt snubber can save the loss (34kW, 0.49%) of conventional snubber circuit in a 7MW back-to-back 3L-NPC VSCs. The proposed snubber has a fewer number of components and improved efficiency.