Low Reverse-Recovery Stress in High-Power Converters Achieved by Self-Resetting Saturable Cores

A clamp circuit using nonlinear reactors is proposed for use with high-power inverters. For stable inverter operation under all typical operation conditions, the cores have self-resetting characteristics by the introduction of an air gap. The circuit configurations are investigated using a 6-kA/6-kV gate commutated thyristor (GCT) chopper. The results are compared to those of a traditional GCT clamp-snubber circuit using a linear anode reactor. New simulation models developed for the cores and diodes are tuned by the experimental results and applied to investigate two- and three-level circuits. Using self-resetting saturable reactors, low freewheel-diode reverse-recovery stress is achieved with a very high value of
di/dt
. The benefits of the new circuit also are demonstrated by mixed-mode device simulation.