Bi-level robust scheduling for multi-terminal DC distribution networks considering uncertainties of loads and renewable energies

Abstract

The randomness of loads and renewable energies affects the security of DC distribution networks. In this paper, a bi-level robust scheduling method is proposed to improve the security and economy of droop-controlled DC distribution networks. The upper-level scheduling aims to minimize the variance of node voltage deviation from rated value with the optimization of voltage source converter (VSC) operation reference power. The lower-level scheduling aims to minimize the power purchase cost with the optimization of energy storage systems (ESSs). Based on the linear power flow model of droop-controlled DC distribution networks, the upper-level scheduling model is converted to a least square programming model and the lower-level scheduling model is converted to a linear programming model, which can be solved with high computation efficiency. In the scheduling model of VSC operation reference power, the uncertain scenarios are directly established based on the linear power flow model of droop-controlled DC distribution networks to improve the calculation speed of robust algorithm. The adjustable confidence intervals of load variations are used to coordinate the robustness and conservatism. The VSC operation reference power and ESS charging/discharging power are coordinated through iterative optimization. The simulation results of two DC distribution networks show that the proposed scheduling method can effectively improve the security and economy of DC distribution networks.