A dynamic nonlinear model for a once-through boiler-turbine unit in low load

Under the background of serious wind and solar energy curtailment in China, flexibility modification of coal-fired supercritical units is selected as an effective technical path to provide space for renewable energy into the grid. Modeling of coordinated control system in low load has yet to be conducted to date. In this work, a simplified dynamic model for coal-fired once-through boiler-turbine unit aimed at low load working condition is built up. First, the major model structure is established mainly based on mass and energy balance laws as well as thermodynamic equilibrium of important parameters combined with the analysis of operation characteristics. Then, the unknown parameters in the model are estimated by regression analysis, statistical analysis, and nonlinear optimization algorithm. Comparison results between measurement and simulation results show that the model has acceptable accuracy and, importantly, also captures the essential dynamic characteristics of units.