Short circuit output protection of MMC in voltage source control mode

The MMC operated in Current Source Mode (CSM) with branch current control shows excellent fault limiting capability. With proper design, the same capability is achieved in Voltage Source Mode (VSM). The key is combining the VSM and CSM controls and having same state variables. Seamless transition between CSM and VSM is ensured by the change of references triggered either by the user or by internal limiters. Experimental results in the full scale 1.25 MW demonstrator proved that the MMCs can limit short circuit currents without turning off even when it's shorted at its terminals.