Coordinated Voltage-Power Control for DC Distribution Networks Based on an Uncertainty and Disturbance Estimator

Abstract

DC distribution networks are low-inertia systems with a range of uncertainties and disturbances. The traditional droop control widely used in DC distribution networks has a contradiction between the accurate power sharing of power units and voltage deviation due to the presence of line impedance. To overcome this contradiction and enhance the immunity and tracking performance of voltage-source converter (VSC) current inner loop PI control, this paper proposes a coordinated voltage-power control strategy based on an uncertainty and disturbance estimator (UDE) for DC distribution networks. Firstly, the improved droop control strategy based on the UDE is proposed, which not only avoids the influence of line impedance on the load current sharing, but also achieves voltage stabilization at the set value. Secondly, an improved VSC current inner loop controller based on the UDE is designed to improve the VSC’s tracking performance for the droop output reference value. The UDE control theory is applied to estimate and compensate for the uncertainties and disturbances of the VSC current inner loop control, in order to improve the tracking and immunity of the VSC current inner loop and enhance the DC voltage robustness. Finally, a three-terminal DC distribution network is taken as an example to verify the effectiveness of the proposed strategy.