Hierarchical Energy Control of MMC-MTDC System Integrated With Offshore Wind Farms for Optimal Frequency Support Provision

This paper proposes an energy coordination control scheme for offshore wind farms (OWFs) integrated modular multilevel converter-based multi-terminal direct current (MMC-MTDC) system towards enhanced grid frequency support. First, a two-layer hierarchical energy control framework is established. At the lower layer, a local energy coordination controller is designed to directly regulate OWF rotor kinetic energy and MMC capacitor energy by using local measurements, eliminating energy utilization errors. At the upper layer, an energy optimization method is developed to dispatch multiple energy for achieving optimal energy utilization and minimizing grid frequency deviations. In addition, a multi-stage energy recovery strategy is designed, ensuring frequency stability during the recovery process and enabling the OWFs-MTDC system to support multiple successive frequency events. Finally, the effectiveness and robustness of the proposed method are verified in a test system jointly built in PSCAD/EMTDC and MATLAB.