Study on adaptive VSG parameters and SOC control strategy for PV-HESS primary frequency regulation

Hybrid energy storage plays a critical role in primary frequency regulation during large-scale renewable energy integration. Rational power distribution between multiple types of energy storage, as well as the use of a VSG control technique, are effective approaches to improving primary frequency regulation capability. To that end, this paper presents an adaptive Virtual Synchronous Generator (VSG) characteristics and state of charge (SOC) management technique for photovoltaic (PV) - hybrid energy storage system (HESS) primary frequency regulation. First, a power distribution mechanism for HESS on the direct current side is implemented. Second, a primary frequency control strategy is proposed based on adaptive rotational inertia and damping coefficient of VSG and SOC regulation of energy storage. Finally, a simulation analysis confirms the feasibility of the proposed primary frequency control strategy under transient conditions. The relevant results are presented as follows. Compared to traditional control strategies, the improved adaptive VSG parameter and energy storage SOC control strategy reduces the overshoot and adjustment time of VSG active power and frequency response by 68.57%, 23.94%, 19.05% and 9.80%, respectively. The decline in SOC of battery energy storage is decreased by 3.18%. The proposed control strategy also limits grid frequency fluctuation within ±0.2 Hz, with a recovery time of less than 0.5 s. The overall root mean square error of frequency f_RMSE is a maximum of 0.02 Hz. The primary frequency regulation capability of the PV-HESS is enhanced, ensuring the operational safety of energy storage systems and effectively improving the stability while also improving grid stability and security.