Stable Equilibrium Control Strategy for Multi-energy Storage SOC Considering Time-varying Linear Resistance

In DC microgrids, it is difficult to ensure the state of charge (SOC) balance among energy storage units due to the complexity of line impedance. Therefore, an improved SOC equalization control strategy considering time-varying linear resistance is proposed. Firstly, the control coefficient is modified by the balance factor which is constructed by line impedance and SOC power index to improve the identification of SOC. At the same time, the output current is used to constrain the balance factor and improve the anti-disturbance ability of the system. After SOC equalization, G becomes 1. At this time, the current distribution can be maintained smoothly by relying on the line impedance information without being affected by line impedance changes. The contradiction between bus voltage quality and SOC equalization control effect is solved by voltage compensation link combined with output current. Secondly, for the problem that the improved control strategy based on SOC balancing is susceptible to constant power load, the mixed potential function theory is used for modeling to obtain the stability criterion, which is conducive to ensuring the stable operation of the system. Finally, the simulation results show that the improved drooping control proposed in this paper can effectively eliminate the influence of line impedance, improve the accuracy of current distribution, achieve the balance of SOC, and verify the effectiveness and correctness of the proposed control strategy under various sudden disturbances and extreme conditions. © 2024 Science Press. All rights reserved.