Research Of A Method Based On Three Impulses In Drum Water Level Controlling In Heat-engine Plant

Boiler drum water level is an important monitoring parameters of the thermalpower plant. High drum water level will affect the separation of water and steam. Onthe one hand it will cause the superheater scaling, on the other hand the steam withwater will cause damage to the turbine blades after entering the turbine. Low drumwater level will cause damage to the water wall, even it can cause an explosion.Therefore maintain the drum water level within a certain range is necessary to ensurethe boiler operate safely and stably. Maintain the drum water level within a certainrange is also an important guarantee for the national economic construction. Internalmodel control method is introduced into the control system of boiler drum water levelwith three impulses in this dissertation. The steam flow signal is imported throw a fuzzyfeedforward controller in order to control the boiler drum water level. The main work isas follows:①Researching the dynamic characteristics of boiler drum water level andAnalysing the impact on the boiler drum water level of each factor. The differencebetween boiler drum water level control system and normal control system in water tankis that the water in boiler drum is in the environment of high temperature and highpressure. There are a large number of bubbles under the water surface. The size of thesebubbles will affect the water level. It means a phenomenon of “false water level” existsin the boiler drum. So a specific control method must be adopted to solve the problem.②The internal model control system is proposed. The characteristics and nature ofthe internal model control are analysed in this dissertation. Then the method to designinternal model controller are introduced. Due to the three impulses control system needto introduce the steam flow signal, fuzzy controller is adopted as a feedforwardcontroller. Then fuzzy logic and the method of designing fuzzy controller are analysedin this dissertation.③A n internal model controller and a fuzzy feedforward controllerare designed inthis dissertation. So a three impulses control system based on internal model with afuzzy feedforward controller is built. Analysis the control effect through simulation withSimulink software and compare the result with dual PID control system. Then changethe model of controlled plant and analysis 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 dual PID control system. Itsovershoot is also less than dual PID control system. When the model mismatch, thesystem can also achieve good control effect. It indicates that the system is of goodrobustness.