Low Reverse Recovery Stress in High Power Converters achieved by Self-Resetting Saturable Reactors

A clamp circuit using non-linear reactors is proposed for the application with high power inverters. For stable inverter operation under all typical operation conditions the cores receive self-resetting characteristics by implementation of a base inductance value in the non-saturated state through air-gap or inductor paralleling. Various circuit configurations investigated by a 6 kA-6 kV-GCT chopper setup are compared to a traditional clamp using a linear anode reactor. New simulation models developed for the cores and diodes are tuned by the experimental results and applied to investigate 2-level and 3-level circuits. Using self-resetting saturable reactors, low freewheel diode reverse recovery stress is achieved especially at small load current even at a very high value of dl/dt.