Efficient modelling of a modular multilevel converter

Looking at the near future, we see that offshore wind penetration into the electrical grid will continue increasing rapidly. Until very recently, the trend has been to place the offshore wind farms close to shore within the reach for transmission using HVAC cables but for larger distances HVDC solutions need to be considered. In the present work are presented methods to simulate the converter without using any kind of semiconductors in order to reduce the simulation time. The model consists only of passive components representing the sub modules in different states. For each state, new values are calculated for the converter. Time-domain simulations on a MMC HVDC test system are performed in the PSCAD/EMTDC software environment based on the new model. The results demonstrate that the modeled MMC-HVDC system with or without converter transformer is able to operate under specific fault conditions.