Dynamic modeling and evaluation of coordinated control system extension for coal-fired power units coupled with a high-pressure steam accumulator

With the increasing penetration of renewable energy in power systems, enhancing operational flexibility of coal-fired power units (CFPUs) is essential for accommodating renewable energy fluctuations and increasing renewable generation share. In this context, integrating energy storage systems with coupled structural and control strategies enabling cooperative operation between CFPUs and storage systems has become an effective retrofit approach to enhance flexibility of conventional CFPUs. Therefore, in this paper, a cost-effective extension of the coordinated control system (CCS) is proposed through integration of a high-pressure small-capacity steam accumulator (SA). A detailed dynamic multi-domain model of a 660 MW ultra-supercritical CFPU is developed and validated in Dymola, and the corresponding CCS is constructed and tuned for various operational scenarios. Based on this model, a coupled energy-supply structure considering regeneration system dynamics is established, and step-response characteristics of the SA under the proposed configuration are analyzed. A multivariable control system enabling SA participation in CCS regulation is further proposed. On this basis, cooperative control algorithms between the CFPU and SA control systems are developed for dynamic and steady-state operations while ensuring turbine safety. Simulation results show that the proposed structure and control framework improve load ramp rate from 1.2 to 1.3 to 2.0 %Pe/min in turbine-following mode and from 1.8 to 5.2 %Pe/min in boiler-following mode, while also significantly improve main steam pressure regulation. Moreover, the cooperative algorithm effectively reduces SA steam consumption and internal thermal fluctuations without compromising flexibility improvement, while also mitigating disturbances to turbine system and reheated steam temperature.