Hierarchical model predictive control of wind farm with energy storage system for frequency regulation during black-start

In high wind power penetration power system, using wind farm equipped with energy storage system (WF-ESS) as black-start (BS) source needs to maintain system frequency stability when starting up ancillary machine or picking up load. A hierarchical model predictive control (HMPC) method of WF-ESS for frequency regulation during BS is proposed in this paper, which consists of two control modes: frequency regulation mode and reserve recovery mode. For the first control mode, a PI controller is used to generate reference power for WF-ESS and to recover system frequency to 50 Hz. The proposed HMPC is divided into WF level and wind turbine (WT) level to accurately track the reference power and guarantee secure operation of each WT. Considering WTs' different operation conditions, WF level MPC distributes reference power to WTs according to the proportion of single WT reserve to total WF reserve. The ESS power is utilized as supplementary when WF output power is insufficient. The rotor speed and pitch angle constraints are included in the WT level MPC while providing frequency response. After frequency deviation is eliminated, WF and ESS are coordinated by the second control mode to avoid a second frequency drop meanwhile reserve a certain proportion of WF available power for managing potential frequency disturbances in the future. A case study is conducted to show the effectiveness of the proposed control method under both low and high wind conditions.