The Study Of Intelligent Control Method For Superheated Steam Temperature In Ultra-supercritical Unit

The superheated steam temperature is one of the main factors to influence the safety and economy of ultra supercritical unit. The main steam temperature must be strictly controlled in order to make sure that the unit works successfully. The dynamic characteristics of the superheated steam temperature control system are great inertial, time-variant, non-linear and so on, so it is difficult to establish accurate mathematical model. Based on studying the mathematical model of the superheated steam temperature, the three intelligent control methods are proposed to control superheated steam temperature, furthermore, the method that the advanced control is used in DCS is also explored.In view of the properties of a lowpass filter of the superheated steam temperature object and the physical properties and dynamic behavior of superheated steam temperature, the improved formula and its application method are proposed. This method can fit dynamic characteristic analysis and real-time simulation in different conditions, so it has the advantages of simplification, convenience and practicability.By the analysis of the relationship between PID control algorithm and mathematic model of thermotechnical process, it can be showed that the error and its derivatives conclude abundant information about thermotechnical process. The information can be used to improve the performance of PID controller. Algorithm of PID control based on intelligent integral is proposed by introducing a new parameter of the rate of free energy dissipation. The proportional gain and integral parameter can be changed dynamically by the algorithm and the response speed and stability can also be raised up. Simulation test about a main steam process of a power boiler shows that the algorithm is prior to conventional PID control.Based on the characteristics of superheated steam temperature of a boiler, a new adaptive fuzzy-PID controller with variable universe is proposed by analyzing human-simulated intelligent control theory to determine its extension factors, meanwhile, the advantages of the cascade controller can still be retained. The system can adjust the parameters of PID controller in its dynamic process on line and it still has the general rule library, strong robustness, well adaptive ability and high control precision. The simulating results show that when the load changes, the system still has fast adaptability, small overshoot, short oscillating period, well static and dynamic performance.An improved Generalized Predictive Control (GPC) algorithm is proposed, which is easy to be implemented in DCS.A simulation test of the superheated steam temperature object of a boiler has been done to demonstrate the correctness of the algorithm. Then the SIEMENS S7-300PLC is chosen as the controller of the system. The improved GPC is programmed successfully on PLC by using the STL language of STEP7. Based on experimental equipment, the superheated steam temperature closed-loop system is set up, and the ideal control performance of intelligent controller can be received.