DC Substation for DC Grid—Part II: Hierarchical Control Strategy and Verifications

DC substation serves as a multiple-input multiple-output system in dc grid for voltage regulation and power dispatching. Based on the dc substation configurations investigated in Part I, a two-layer hierarchical control strategy is proposed with simultaneous terminal voltage/current control aims. The primary layer is implemented on single-input single-output converters, working for voltage regulation and internal current control. The secondary layer serves for current regulation at the output terminals and substation loss optimization. Hierarchical control of ring-type dc substation is taken as an example, with consideration of dynamic coupling among the internal converters. The proposed control strategy is compared with centralized control and verified through numerical simulations. A downscaled experimental dc grid has been built, and the hierarchical control strategy is implemented on a dc substation prototype with a distributed controller.