Disturbance Management in a DC Grid using a Hierarchical Control Structure

DC grids will play a key role in the future, interconnecting generation and load centers as well as energy markets. Large multi-terminal VSC-HVDC systems of high capacity will require automated coordination for several operation scenarios especially when operating under disturbances. With this in mind, and considering the dynamics of a DC system, communication loss events are considered severe disturbances in the operation of the multi-terminal system along with major electrical faults such as 3-phase faults on the AC sides of the converters that require considerable coordination efforts. This work aims at enabling the multi-terminal system with communication loss ride-through and automatic post-fault rescheduling capabilities. This is achieved within a hierarchical control structure whose features are briefly described. A 3-terminal VSC-HVDC system is modelled for the needs of demonstration under different operation scenarios. Communication loss ride-through capability is demonstrated by comparing the behavior of the 3-terminal system during a normal operation scenario and a worst-case scenario where communications with all-three terminals fail. Its behavior does not change but since communications fail, the operation is uncoordinated greatly reducing the security of the system regarding upcoming events. During 3-phase faults DC droop performs the primary control stabilizing the system. Secondary control is performed by the overall control after the system state is identified. Automatic, post-fault rescheduling takes place in an effort to follow the power flow schedule where possible without exceeding substation limits. (Less)