<p>To solve the power fluctuation and system stability problems caused by large-scale wind power grid connection, this study proposes a capacity optimization configuration and stability improvement strategy for wind power generation and battery-supercapacitor hybrid energy storage systems. In view of the shortcomings of traditional energy storage configuration methods that fail to take into account full life cycle economics and dynamic stability, this study established a two-layer optimization model with the goal of lowest annual average cost throughout the life cycle and minimal grid-connected power fluctuations, and designed a set of power allocation strategies based on frequency decoupling. The results revealed that the model proposed in the study was better than four advanced algorithms in optimization performance, and the Pareto front obtained reached the highest 0.782 in the hypervolume index. The optimized configuration achieves a minimum annual average cost of 1.887 million yuan and limits the grid-connected power fluctuation standard deviation to 124.6&#xa0;kW. Compared with a single battery energy storage solution, the optimally configured hybrid energy storage system could not only further reduce the standard deviation of grid-connected power by 6.7%, but also reduce the average daily equivalent number of battery cycles by 38.5%. Stability analysis verified that the hybrid energy storage system solution could increase the damping ratio of the system’s dominant oscillation mode from 0.058 for a single battery to 0.124, and shorten the voltage recovery time by 21.2% under a three-phase short-circuit fault. The method proposed in the study provides a systematic solution that takes into account both economy and safety for energy storage system planning under high-proportion wind power access, and has important theoretical value and engineering application prospects.</p>