Dynamic modeling and active disturbance rejection control for the flue gas-molten salt thermal energy storage system

Integrating molten salt thermal energy storage (TES) is an effective approach to enhance the operational flexibility of coal-fired power plants. To reveal the dynamic characteristics of the flue gas-molten salt TES system, this study develops a four-input and three-output control-oriented dynamic model that captures the energy transfer and coupling mechanisms between flue gas and molten salt. Based on this basis, a composite control strategy integrating linear active disturbance rejection control (LADRC) with feedforward compensation (FF) is proposed. In this strategy, LADRC performs online estimation of total disturbances and implements feedback regulation, while the feedforward compensation counteracts partially known disturbances, thereby mitigating the adverse effects of large thermal inertia and time delay. Simulation results demonstrate that when the thermal storage power setpoint changes by 25%, the settling time of the FF-LADRC scheme is reduced by 5.6% and 55.8% compared with LADRC and PID, respectively. When the outlet molten salt temperature is step-increased from 390 °C to 400 °C, the maximum dynamic deviation of thermal storage power under the proposed strategy is reduced by 40.8% and 94.5%, respectively, compared with the other two schemes. Under flue gas mass flow disturbances, the settling times of system output variables are significantly shortened with the FF-LADRC scheme. Under inlet molten salt temperature disturbances (a step increase from 220 °C to 230 °C), the mean absolute error of the thermal storage power is reduced by 7.40% and 81.4%, respectively. The proposed control strategy significantly improves the dynamic performance and disturbance rejection capability of the flue gas-molten salt TES system, demonstrating strong potential for engineering applications.