A Dynamic Nonlinear Model of Once-Through Boiler Turbine Units with Superheated Steam Temperature

With recent development of renewable energy, the once-through boiler-turbine (OTBT) units in China are required to improve operating flexibility in order to absorb more renewable energy integrated into power grid. However, it is a challenge for control systems to provide load following capability while maintaining safe operation. To this end, this paper proposes a dynamic nonlinear model of OTBT units by incorporating superheated steam temperature dynamics. Model structure is derived from mass and energy conservation laws by using a lumped parameter method, and parameters and functions in the structure are identified by using an optimization algorithm with running data. Besides, the model proposed contains the influence of total spray water flow on steam enthalpy in separator and on superheated steam temperature. Validation results show that the proposed model has acceptable steady-state and dynamic accuracies as well as a proper physical structure, and it can be used for controller design to improve control performance.