DC voltage control and power dispatch study of a five-terminal DC grid based on average-value VSC model

DC grids based on voltage source converters (VSCs) are proposed for integrating large windfarms and delivering remote energy source power through long distance. A number of DC voltage control and power dispatch strategies are presented by researchers to guarantee the power transmission flexibility and capacity of such DC grids. Various options for ensuring satisfactory steady-state and dynamic-state system characteristics are discussed in the paper. A novel control strategy is proposed to achieve the goal of both precise DC voltage tracking under normal operation and steady control mode conversion after slack-bus terminal loss. PSCAD/EMTDC simulations on a five-terminal DC grid with four onshore VSC terminals and one offshore VSC terminal during wind power variation and onshore VSC terminal loss are presented to show the robust performance of the proposed control strategy. Further studies on the loss of master terminal during severe fault are provided to validate the positive effect of dynamic braking resistor (DBR).