DC voltage droop gain for a five-terminal DC grid using a detailed dynamic model

Droop gains in direct current (DC) transmission grids are commonly studied using static indicators like V-I curves and power-sharing calculations. The dynamic studies of voltage source converters high-voltage DC have been challenging because of numerous control loops and complexities in DC-alternating current interactions, which is becoming even more challenging with converter to converter interactions in DC grids. This paper firstly presents a 126th-order multiple-input multiple-output small-signal dynamic linearized model of a five-terminal DC network, which includes all converter dynamics and controls in detail. The model accuracy is verified against a detailed benchmark model in PSCAD. The model is then employed to design DC voltage droop control at each of the four terminals considering the dynamics and transient behavior of the DC network. A root-locus study is used to find the optimum values of the droop gains and the cutoff frequency of the DC voltage feedback filters. The PSCAD model is employed to verify the design results and also to test large disturbances like converter tripping in the test DC grid. The study highlights the benefits of DC droop control and also points the possible dynamics instabilities with incorrectly tuned droop parameters.