Two-Time-Scale Coordinated Energy Management for Medium-Voltage DC Systems

In medium-voltage DC (MVDC) systems, to manage the impacts of uncertainty and variability brought by the high-penetrated renewable energy sources (RES), this paper proposes a two-time-scale coordinated energy management method. Based on a hierarchical control framework, the droop control is used and its two key factors, operating point and droop coefficient, are co-optimized. To improve operational benefits, operating points are determined in the reference optimization, considering the long-term cooperative operation of various integrated units. To enhance system security, droop coefficients are optimized in the coefficient optimization, where controllers' responses to the system unbalanced power and changes of system voltage profile within the dispatch interval are both considered. Since these two optimizations are performed in different time scales, a two-time-scale coordinated strategy is designed to balance long-term economic benefits and short-term security performance. The proposed approach is verified on a typical MVDC system which has a meshed network topology. Conventional and renewable energy sources as well as schedulable and unschedulable load demands are considered. Numerical experiments indicate that, the proposed approach is capable of providing economical and reliable dispatch, such that the forecast errors and fluctuations brought by the high-penetrated RESs and other unschedulable units can be adapted to.