Impact of droop coefficient on dynamic voltage stability of DC Grid

Coordinating control strategies of DC grid include master slave control, voltage margin control and voltage droop control, etc. Droop control could achieve several DC voltage control of DC grid, but the droop coefficients would impact on the dynamic voltage stability of the system. In this paper, modular multilevel converters (MMCs) based DC grid is the main study object. Firstly, the DC side voltage control system model and its transfer functions of the MMCs with droop control are derived. Then, a reasonable value range of droop coefficients that would maintain the system stability is presented by Routh criterion. And the influences of selection of droop coefficients in different ranges on voltage stability are analyzed. Finally, a four-terminal DC grid model is established on PSCAD/EMTDC, and the influence on voltage adjustment and stability of DC grid under different droop coefficients is simulated and analyzed. The simulation results verified the correctness of the theoretical analysis.