Nonlinear-backstepping-based Coordinated Control For Boiler-turbine Units

A boiler-turbine coordinated control system is the control center of a power generation unit, and is the core of a modern power plant. This dissertation studies the design and implementation of the boiler-tubine unit coordinated control system for a classic nonlinear model of boiler-turbine units via nonlinear backstepping control theories and methods, with the motivation to apply advanced control strategies to engineering practice and to improve the adaptability of the coordinated control system to the process multi-variable coupling, nonlinearities and uncertainty of parameters.The main contributions of this dissertation are summarized as follows:â‘ The nonlinear model of boiler-turbine units is linearized, and is decomposed to get the core of the control. The controller of the core is designed by using backstepping method, and is changed into PID form for engineering purpose. Then the backstepping coordinated controller is obtained by using the relationship between the core and the whole linearized model. Simulation studies of the backstepping coordinated control system based on the linearized model are done on a 500MW boliler-burbine unit, the results of which demonstrate that this control strategy has good ability to overcome the object coupling.â‘¡Retaining all the nonlinear information of the nonlinear model of boiler-turbine units and in accordance with the characteristics of the model and the using conditions of backstepping, the model is pretreated. After pretreatment, the system is divided into two subsystems. Then nonlinear backstepping controllers are designed for the subsystems separately, and the nonlinear backstepping coordinated control law is obtained and changed into PID form for engineering purpose. The designed nonlinear backstepping controller is applied to the 500MW nonlinear model. Simulation results show that this kind of control strategy can well overcome the coupling and nonlinear of the object.â‘¢Based on the design of nonlinear backstepping coordinated control system, and taking into account the impact of system ajust quality caused by uncertain parameters, the nonlinear adaptive backstepping coordinated controller is designed and changed into PID form. Simulations on the nonlinear model of the 500MW boiler-turbine unit show that the addition of adaptive link effectively offset the impact of uncertain parameters on the system.â‘£Through time series analysis methods, time series models is fitted to the routine operation data of the designed boiler-turbine unit backstepping coordinated control systems. From these models the feedback-invariant forms of the control systems are extracted, which are used for estimating minimum variances. Then based on the benchmark of practical minimum variance, the control performances of the designed three coordinated control systems are evaluated and compared.