Despite the rapid growth of wind energy, its inherent variability and uncertainty introduce significant challenges for power system operation. Power fluctuations, reduced power quality, and difficulties in meeting grid code requirements become more pronounced at higher penetration levels. Energy storage systems (ESS) have therefore gained increasing attention as an effective solution, enabling power smoothing, improving system stability, and supporting grid services such as frequency regulation and low-voltage ride-through (LVRT).

In this context, this work focuses on the selection of hybrid energy storage system (HESS) technology, its integration architecture, and the development of a unified framework that simultaneously considers power smoothing, LVRT, and frequency support requirements. A modified mean-value dispatch strategy with a predefined regulation band is introduced to reduce power fluctuations while minimizing storage capacity. In addition, a hierarchical control framework is developed to enable coordinated power allocation between storage units while incorporating state-of-charge (SOC) constraints.

The study utilizes one hour of wind data to evaluate power smoothing performance. Dispatched power references are generated using mean-value, min–max, and ramp-rate-limited methods for comparison. The proposed band-limited mean-value strategy aims to reduce ESS size while satisfying grid code requirements. The HESS sizing is carried out using a multi-objective approach that considers power smoothing, LVRT conditions, and frequency support requirements.

A coordinated control framework is implemented for different operating modes, including normal operation, voltage disturbances, and frequency events. During normal operation, power is allocated between storage units using low-pass and high-pass filters. During voltage disturbances, the HESS absorbs excess energy at the DC link, with the supercapacitor providing fast dynamic response and the battery contributing when required. During frequency events, the supercapacitor provides inertial response, while the battery supplies sustained frequency support, considering SOC constraints.

The results demonstrate that the proposed framework effectively determines the required HESS capacity for a 7 MW PMSG-based wind turbine system. For power smoothing under a ±5% regulation band, a HESS capacity of 154 kWh and a rated power of 2.7 MW are obtained, operating within a 0.6 SOC window.

During LVRT conditions, the HESS maintains the DC-link voltage at 1200 V while the generator continues operating at maximum power point tracking (MPPT). The required energy absorption is approximately 1.47 kWh over a 1.5 s recovery period, significantly reducing the dependence on braking choppers.

Furthermore, the HESS successfully provides inertial response and frequency support without affecting MPPT operation. To emulate a virtual inertia of 3 s under the German worst-case scenario (RoCoF = −2 Hz/s, Δf = 1 Hz), a peak inertial power of 1.68 MW and an energy of 0.233 kWh are required. The corresponding frequency-support power is 2.8 MW, with energy requirements of 7.78 kWh and 23.33 kWh for 10 s and 30 s durations, respectively.