Research On DCS-base Three-impulse Level Control Of Thermal Power Boiler

Boiler drum water level is key monitoring parameters of the thermal power plant.High drum water level will affect the separation of water and steam.On the one hand it will cause the superheater scaling,on the other hand,the steam with water will cause damage to the turbine blades after entering the turbine.Low drum water level will cause damage to the water wall,even it can cause an explosion.It is an essential condition to ensure the boiler operating safely and stably that maintaining the drum water level within a certain range.Therefore,an internal model control method is introduced into the control system of boiler drum water level with three impulses in this thesis.The steam flow signal is imported by a fuzzy feedforward controller in order to control the boiler drum water level.The main work is as following:Researching the dynamic characteristics of boiler drum water level and analyzing the impact on the boiler drum water level of each factor.The difference between boiler drum water level control system and normal control system in water tank is that the water in boiler drum is in the environment of high temperature and high pressure.There are a large number of bubbles under the water surface.The sizes of these bubbles will affect the water level.It means a phenomenon of "false water level" exists in the boiler drum.So a specific control method must be adopted to solve the problem.The internal model control system is proposed.The characteristics and nature of the internal model control are analyzed in this paper.Then the method to design internal model controller are introduced.Due to the three impulses control system need to introduce the steam flow signal,fuzzy controller is adopted as a feedforward controller.Then fuzzy logic and the method of designing fuzzy controller are analyzed in this paper.An internal model controller and a fuzzy feedforward controller are designed in this dissertation.So a three impulses control system based on internal model with a fuzzy feedforward controller is built.Analyzing the control effect through simulation with Matlab/Simulink software and comparing the result with traditional PID control system.Then,changing the model of controlled plant and analyzing the result when the model mismatch.The simulation result shows that internal model control system with fuzzy feedforward is more quickly and more accurate than PID control system.Its overshoot is also less than PID control system.When the model mismatch,the system can also achieve good control effect.It indicates that the system is of good robustness.