Task 4.2.1: Fault Management in Fault Current Limited MVDC Systems

The characteristic of the rotating machines, which normally dominate the system behavior under fault conditions in AC systems, can be completely decoupled from the MVDC distribution system if certain converter topologies such as full bridge modular multi cell (MMC) converters or “active power distribution nodes” are employed. Note, that while SCR-type converters can interrupt fault currents at the next zero crossing of the AC current significant transients remain on the DC side. Moreover, fast interruption may not leave enough time to identify the fault location in meshed systems. However, employing converters which limit the fault current on the DC side to levels around nominal current values open up the opportunity to essentially eliminate the impact of high transient fault currents on the MVDC side. This in turn is expected to have substantial impact on the overall MVDC system design (no DC breakers, substantially reduced bracing against dynamic forces, etc.). Therefore, building upon work conducted previously at USC, this subtask seeks to develop and demonstrate a complete "fault current free" MVDC system.