Recently, widespread adoption of renewable energy significantly impacts the security and stability of power grid. Utilizing coal-fired units in real-time load figuration remains a primary method to ensure grid stability. Therefore, supercritical Once-Through Boiler-Turbine (OTBT) units continuously enhance flexibility to meet the evolving needs of the grid. To broaden the load boundary and achieve fully automated control from unit start-up to rated load, establishing a dynamic mathematical model used for controller design of OTBT units in all load conditions is a necessary prerequisite. This model should accurately predict model outputs in both once-through mode (OTM) and recirculation mode (RCM) while also reflecting the dynamic transition processes between modes. In this study, we first conducted a detailed analysis of the characteristics of recirculation system. Mass and energy conservation equations are established separately for economizer-waterwall system and superheater system, including a level model for storage tank in RCM. Subsequently, through reasonable assumptions and analysis of the transition process, the modified steam dryness is identified as a crucial indicator to distinguish between RCM and OTM. This approach unified the model structures in RCM and OTM, avoiding issues related to model switching during mode transitions. Following this, model parameters were identified based on an improved dynamic search fireworks algorithm. Finally, multiple sets of comparative simulation experiments demonstrated that the established model exhibits high accuracy throughout the unit operation. Results from open-loop simulations indicated that this model can serve as a foundation for controller design of coordinated control system in all load conditions.

中文翻译：

---

全负荷工况超临界直流锅炉机组控制器设计的动态数学模型

近年来，可再生能源的广泛应用极大地影响了电网的安全稳定。利用燃煤机组进行实时负荷配置仍然是确保电网稳定的主要方法。因此，超临界直流锅炉汽轮机 (OTBT) 装置不断增强灵活性，以满足电网不断变化的需求。为了拓宽负荷边界，实现从机组启动到额定负荷的全自动化控制，建立用于OTBT机组全负荷工况控制器设计的动态数学模型是必要的前提。该模型应准确预测直流模式（OTM）和再循环模式（RCM）下的模型输出，同时反映模式之间的动态转换过程。在本研究中，我们首先对再循环系统的特点进行了详细的分析。分别建立了省煤器-水冷壁系统和过热器系统的质量和能量守恒方程，包括RCM储罐的液位模型。随后，通过合理的假设和对转变过程的分析，将修正后的蒸汽干度确定为区分RCM和OTM的关键指标。这种方法统一了RCM和OTM中的模型结构，避免了模式转换期间与模型切换相关的问题。随后，基于改进的动态搜索烟花算法来识别模型参数。最后，多组对比仿真实验表明，所建立的模型在整个机组运行过程中表现出较高的准确性。开环仿真结果表明，该模型可以作为所有负载条件下协调控制系统控制器设计的基础。