Coordinated Control Of Unit Plant Based On Backstepping Design Method

As a kind of energy driven by electric energy,electric power is closely related to the development of national economy.According to the data of China Electricity Council,most of Chinese electricity is generated by coal-fired power generation.In China,Unit plant composed of a boiler and a steam turbine is widely used in coal-fired power generation.The start and stop of each equipment and the coupling between equipments greatly reduce the operation performance of Unit plant.Therefore,it is an unremitting pursuit to make the coal-fired power generation production process more efficient.Furthermore,Unit plant is multivariable and strongly coupled,and it has uncertain parameters as well as obvious nonlinearity.As the operating conditions of Unit plant change,the dynamic and static characteristics of each equipment change significantly.A large number of uncertain disturbances and delays are concentrated on the boiler side,which results in serious structural asymmetry between equipments.These complex system characteristics bring challenges to the control of Unit plant.In this thesis,the coordinated control scheme is adopted with the consideration of the asymmetry between boiler and steam turbine.The instructions of load command and main steam pressure act on the boiler controller and steam turbine controller at the same time,and change the boiler fuel input and the opening degree of steam turbine valve in parallel.The scheme not only makes the output power and main steam pressure equal to the set value as soon as possible,but also maintains the dynamic energy balance between the boiler input side and the steam turbine output side.Based on the above idea of coordinated control,the research content of the thesis is divided into the following two aspects:(1)Backstepping coordinated control of actuator saturated nonlinear Unit plantBased on a typical nonlinear Unit plant with actuator saturation,the nonlinear backstepping coordinated controllers are constructed based on the backstepping design method in chapter 3 firstly.The main operating parameters of Unit plant can remain stable while the output power of Unit plant tracks the load signal of the external power grid.Secondly,the coordinated control strategy of Unit plant based on static gain method is proposed to overcome the "differential explosion" resulted from the continuous derivation of the virtual controller in this chapter.At last,simulation verification on a 500MW nonlinear Unit plant model is conducted to prove the effectiveness.From the simulation results,it can be seen that nonlinear backstepping coordinated controllers designed in this chapter can successfully overcome the adverse impact of the essential nonlinear characteristics of Unit plant and the coupling between variables on the operating.And it also can be concluded that the controllers have good output tracking ability and disturbance rejection performance.Different from previous studies,the opening degree of the steam turbine valve is limited with the actual operation of Unit plant changes is considered.Therefore,the auxiliary system is introduced to handle input saturation and restrain the adverse effect on the Unit plant operating in this chapter.The opening degree of the steam turbine valve can be limited to a reasonable range.(2)Adaptive backstepping coordinated control of uncertain nonlinear Unit plantAimed at a typical nonlinear Unit plant with uncertain parameters,the controllers of boiler and steam turbine and the update rates of uncertain parameters are constructed based on the adaptive backstepping design method in chapter 4 firstly.Unit plant can not only have good performance near the fixed load point,but also can track the load signal of external power grid.The Laplace transform is introduced to convert the form of controllers and update rates of uncertain parameters into PID form in order to enhance the practicability of engineering in this chapter.Secondly,an improved backstepping design method is proposed to overcome the"differential explosion" problem resulted from the continuous derivation of backstepping design method in this chapter.Finally,Simulation verification on a 500MW nonlinear Unit plant model is conducted to verify the effectiveness.From the simulation results,it can be proved the controllers designed in chapter 4 has certain disturbance rejection performance,which greatly improves the control performance of the system when the model parameters of Unit plant are mismatched and the ability of Unit plant to operate in a wide range and under variable conditions.Different from previous studies,the uncertain parameters affecting the operation performance of the system is fully considered in this chapter.Based on the nonlinear adaptive backstepping PID method,the controllers and the update rates of uncertain parameters of Unit plant coordination system are proposed,which can well offset the adverse impact of uncertain parameters on the actual operation of the system.