Iranian Research Organization for Science and Technology (IROST) Hydrogen, Fuel Cell & Energy Storage 2980-8537 13 1 2026 01 03 Analysis of the Impact of Energy Storage Units on Frequency Regulation Stability in Hydrothermal Power Plant Using State Space Modeling 1 16 1542 10.22104/hfe.2025.7384.1342 EN Mahnaz Hashemi Department of Electrical Engineering, Na.C., Islamic Azad University, Najafabad, Iran Digital Processing and Machine Vision Research Center, Na.C., Islamic Azad University, Najafabad, Iran 0000-0002-7454-6423 Ghazanfar Shahgholian Department of Electrical Engineering, Na.C., Islamic Azad University, Najafabad, Iran Smart Microgrid Research Center, Na.C., Islamic Azad University, Najafabad, Iran 0000-0003-2774-4694 Mehdi Riahinasab Department of Electrical Engineering, Na.C., Islamic Azad University, Najafabad, Iran Smart Microgrid Research Center, Na.C., Islamic Azad University, Najafabad, Iran 0000-0003-1059-0510 Ehsan Hosseini Department of Electrical Engineering, Na.C., Islamic Azad University, Najafabad, Iran Department of Electrical Engineering, Cadiz University, Cadiz, Spain 0000-0003-4693-9008 Journal Article 2025 07 11 Energy storage systems have been considered in the last few years to improve the performance of energy grids. In a typical power system, an instantaneous balance between generated and consumed power must be maintained, without storing energy. As a result, the power generation must follow the load curve, and due to the variability of electrical demand, the operation of the energy grid may not be economically efficient. Balancing total generated power with total demand, while accounting for losses, requires optimal performance of the electric power system. Consequently, one of the critical components in any energy network is its ability to regulate load frequency effectively. This study investigates the effect of an energy storage system on enhancing load frequency regulation performance in an interconnected energy network comprising two-area steam and hydropower plants. Initially, the energy grid model, incorporating a superconducting magnetic energy storage (SMES) unit, is expressed in state space using first-order differential equations. Subsequently, the effect of the energy storage system on the power network is explored through system mode analysis. Results from time-domain simulations conducted in MATLAB demonstrate the effectiveness of the system mode investigation and its responsiveness to load fluctuations, confirming the reliability of the approach. https://hfe.irost.ir/article_1542_d010396ca8abf6ead8cacc2c2f2f26c7.pdf