Novel protection strategy for current interruptions in IGBT current source inverters

A novel protection strategy against dc link overvoltages in IGBT current source inverters caused by current interruptions is presented. The proposed concept consists of two steps-a fast passive voltage clamp and actively turned on freewheeling paths across the dc link terminals. To implement this strategy, an electronic circuit was developed and successfully tested. The protection circuit is completely independent from normal inverter operation, has no effect on the CSI behaviour and can be realized at low cost.