Frequency Consensus Control for Two-area Flexible DC Interconnected System

In order to improve frequency stability of two-area flexible DC interconnected system, a frequency consensus control based on ‘local control’ and ‘upper coordination’ is proposed in this paper. 1) ‘upper coordination’ generates DC voltage reference for ‘local control’ in order to realize frequency consensus control by collecting local voltages and designing DC voltage control law reasonably. 2) ‘local control’: local controllers of voltage terminal VSCs and power terminal VSCs can respond to frequency fluctuations of local grid simultaneously while achieving corresponding control targets (voltage control or power control). No matter which grid suffers power disturbance, frequency dynamic of the disturbed grid can be improved, frequency deviation can be shared by all AC grids and spinning reserves sharing can be realized of the whole system with the proposed control method. Moreover, the proposed method has less dependence on communication, and even when communication system fails, the DC system can still provide frequency supporting for the disturb grid to a certain extent only with local information. The effectiveness of the proposed control was verified by simulation in PSCAD/EMTDC.