Frequency regulation optimization for thermal-wind-storage systems considering unit characteristics and energy storage state of charge recovery

With the continuous rise of renewable energy penetration in China's power system, thermal-wind-storage systems need to carry out joint frequency regulation response according to their unit characteristics. To improve the automatic generation control (AGC) response capability and economy of units, a joint frequency regulation optimization method for thermal-wind-storage systems is proposed, which considers the output characteristics of thermal-wind units and the state of charge (SOC) recovery of energy storage. Firstly, the boundary conditions for initiating SOC recovery at each energy storage station are defined based on operating conditions including the predicted output of wind turbines and the available capacity of energy storage. Secondly, based on this boundary and real-time frequency regulation commands, a multi-objective optimization model is established with three objectives: minimizing the output deviation of thermal units, minimizing the response cost, and maximizing the SOC recovery efficiency of energy storage. A combination scheme of fuzzy preference selection method and weighted sum method is applied to the objective function values of the solution set from the model, and the optimal scheduling strategy is obtained through scoring and ranking. Finally, a case study on a typical regional power grid verifies that the proposed model can effectively reduce the output deviation caused by thermal units, improve frequency regulation stability, decrease frequency regulation response cost, enhance frequency regulation economy, improve frequency regulation sustainability of energy storage resources, and strengthen overall system frequency regulation capability.