A Distributed Cooperative Control Based on Consensus Protocol for VSC-MTDC Systems

A distributed cooperative control (DCC) strategy based on the consensus protocol is proposed for providing frequency support through voltage source converter based multi-terminal direct current transmission (VSC-MTDC) systems. The DCC consists of a local P-V droop controller and a cooperative agent network for cooperation control. Each agent controller is composed of a frequency regulation subagent (FRA) for frequency support and a load ratio subagent (LRA) for balancing the power sharing amongst the stations connected to the same ac grid. Moreover, to reduce the impact of the communication link failure, a topology evaluating method is proposed to select the suitable topology of the communication network via graph theory. The small signal stability analysis and the steady-state analysis are performed to investigate the stability and the consensus performance of the VSC-MTDC systems with DCC. Compared with decentralized control, the DCC can simultaneously achieve better frequency support and power sharing without leading to a large dc voltage deviation. The effectiveness of the DCC is verified by simulations on a hybrid ac/dc grid with a 7-terminal VSC-MTDC in DIgSILENT/PowerFactory under the load step change event and communication failure event.