Primary frequency regulation (PFR) is a crucial operating condition for PSPs to realise frequency modulation, and the effectiveness of PFR is significant to the stability of power system frequency. Several challenges and risks have been presented in the PFR process for conventional PSPs, especially for those which run in the isolated grid, such as water inertia, negative damping of speed governor and ultra-low frequency oscillation (ULFO). Variable-speed pumped storage plants (VSPSPs) have the potential to overcome the negative impacts on regulation performance caused by hydraulic factors, due to the advantages of rapid power regulation and independent active power control from turbine output. In this paper, the primary task is to conduct a comprehensive assessment for PFR performance of VSPSPs in isolated power systems. Initially, the hydraulic–mechanical–electrical numerical models are established. Secondly, the rotational speed stability of the pump-turbine is quantified and the advantages of VSUs in suppressing ULFO are assessed. Relevant results reveal that the performance of VSUs is better than that of FSUs in the regulation process. Finally, assessments of frequency regulation performance under various scenarios are conducted with four indicators (standard deviation of power differences, power regulation time delay, settling time and overshoot).

The increase of renewable energy generation penetration rate exerts a passive impact on the power system. A pumped‐storage plant (PSP) is a proper technology to depress power fluctuation and regulate the frequency of the power system. Variable‐speed PSP (VSPSP) is a relatively novel technology and has unique advantages when participating in power and frequency regulation. This study focuses on the generating phase modulation of VSPSP and fixed‐speed PSP (FSPSP). The integrated hydraulic‐mechanical‐electrical models of FSPSP and VSPSP are built and vector control theory is introduced in the model of VSPSP. Based on these two models, this study analyses operational performance and power response under generating phase‐modulation mode. The results reveal that the power regulation ability of VSPSP is more accurate and rapid. In addition, the operation of VSPSP is not restricted by a stability limit and the range of power regulation is expanded. Eventually, it could be observed that weak coupling between the mechanical and electrical system in VSPSP helps to increase efficiency and prolong life‐span of pumped‐turbine. The results and conclusions obtained from this study help to mitigate power fluctuation and improve strategies of power regulation of hybrid power systems with PSP.