Multi-Objective Optimization-Based Frequency Regulation Control of Grid-Forming Wind-Storage Systems
Liu Huiqiang1,2, Ren Yongfeng1, Meng Qingtian1,2, Zhang Yan3, Li Shubao3
1. School of Energy and Power Engineering Inner Mongolia University of Technology Hohhot 010080 China; 2. Inner Mongolia Electric Power Research Institute Hohhot 010020 China; 3. School of Electrical Engineering Xi’an Jiaotong University Xi’an 710049 China>
Abstract:Grid-forming wind-storage systems can provide active power support and are applicable to improving grid stability and system dynamic performance in new-type power systems. Their frequency response is highly sensitive to operating states and dynamic conditions, while existing frequency regulation strategies exhibit three main limitations: (1) during transient frequency support, the bidirectional dynamic coupling constraints between the energy storage state of charge (SOC) and wind-turbine rotor kinetic energy are not sufficiently modeled or enforced; (2) the storage droop coefficient and charge/discharge depth are not adaptively coordinated with SOC; and (3) a unified modeling-and-control framework that links wind-storage coupling mechanisms with multi-objective performance optimization remains unavailable. These issues motivate the development of multi-objective, multi-constraint cooperative control strategies to strengthen active power support capability. A hierarchical coordinated frequency regulation method is developed for grid-forming wind-storage systems. At the wind-turbine layer, an adaptive control strategy is formulated by explicitly incorporating both SOC constraints and rotor kinetic-energy constraints. Active power is regulated according to grid operating requirements, enabling frequency support while limiting excessive kinetic-energy extraction and avoiding storage over-discharge, thereby reducing wind curtailment and improving the available reserve margin of the wind-storage system. At the energy-storage layer, an adaptive frequency regulation strategy is designed by jointly considering SOC and charge/discharge depth constraints. The droop coefficient and the allowable power command are adjusted online to comply with storage safety boundaries and to maintain controllability across different SOC levels, so that storage power can be modulated safely and efficiently under varying operating conditions. At the coordination layer, a rolling multi-objective explicit model predictive control (MO-EMPC) strategy is constructed. The rolling optimization explicitly accounts for wind power reserve constraints, rotor speed stability requirements, and energy-storage safety limits, and coordinates the wind-storage power allocation through multi-objective optimization. The coordinated strategy aims to improve frequency response performance while maintaining feasible operating margins for both the wind turbine and the storage system under diverse operating points. Numerical simulations are performed to evaluate the proposed control scheme under multiple operating conditions. The results show that the wind-turbine dynamic adaptive control method with dual SOC-rotor kinetic-energy constraints can reshape turbine operating characteristics in real time, effectively reducing wind curtailment and increasing the reserve margin of the wind-storage system. The SOC and depth-aware storage adaptive frequency regulation strategy enables dynamic and flexible storage power regulation, improving the safe operating capability of the energy storage system and increasing power utilization efficiency by preventing excessive charge/discharge depth at unfavorable SOC levels. The rolling MO-EMPC-based multi-objective coordinated control further enhances fast frequency response capability and frequency stability across different operating conditions. Compared with conventional methods, rotor-speed recovery is smoother, the maximum storage depth of discharge under low-wind-speed conditions is reduced by 22.64%, and the steady-state frequency deviation is reduced by 7.04%. These results indicate that coordinated consideration of wind power reserve constraints, rotor speed stability, and storage safety limits can improve operational reliability and achieve coordinated enhancement of dynamic power support capability and frequency response performance in grid-forming wind-storage joint frequency regulation systems.
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