Hierarchical control system of modular multilevel converter used in high-voltage direct current transmission

Based on cascade of MMC power units, the simple topology of Modular Multilevel Converter (MMC) tends to meet the need of High voltage direct current transmission (HVDC) more easily than other topologies. However, following the rising of voltage level, the number of MMC power unit increases and put forward high performance request for the control system. In these cases, using traditional centralized control system may seriously affect the feasibility and reliability of MMC system. This paper proposes a novel hierarchical control system constituted by a main controller, valve controllers and unit controllers. Relevant hierarchical control method was designed and has been verified by simulation and experiments.