Study On Fuzzy Control Method Applied To Time Delay System

Nowadays, many countries in the world are paying more and more attention to the subject of energy's sustainable development. Corresponding measures have been established to improve environmental protection level and control of pollution effluent standard is more and more strict. So, for power industry, it's necessary and urgent to develop clear and high efficient electric power generation technology. Considering present energy condition and level of power technique in our country, it's necessary to actively develop supercritical technology, one of clear coal electric power generation technology.At present, our government has put forward develop plans of relative projects to support and promote application of supercritical technology in our country.But with the unit capacity augmented and parameters increased, constituent systems have to been more effective to meet unit's higher expectation. For boiler operation's security and economy, power plant control method is one of important subject to develop.Systems in power plant always represent typical time-delay, inertia characteristic. And in practical production, because of changes of work condition, they also display obvious time-varying and indeterminacy characteristics.Generally, PID control is adopted in power plant. These control method can get satisfied control result under normal work condition. But conventional PID control requires controlled device has exact mathematic model, which exposes this method's shortage when subject's character changes. In fact, conventional control method is based on exact mathematic model and adopts inaccurate model and fixed control algorithm. So the control system lacks of adaptability and is difficult to match the expectation of complex system control.So people hope to combine intelligent control and conventional control to make full use of favorable factors. The new method is expected that it can get satisfied result even meeting delay and indeterminate subject.Fuzzy control is a branch of intelligent control. Fuzzy algorithmic is quite proper to apply to system whose model is uncertain. But common fuzzy controller still cannot meet the expectation when used in time-delay, inertance system. So it's necessary to unite other algorithm to improve control performance. This paper designs two kinds offuzzy controller for time-delay system based on analyses of fuzzy control and other control methods, that is modified Smith controller for delay process and fuzzy increment based on history(FIBH).Modified Smith controller is based on analyses of traditional Smith predicted control system's disadvantage in practice control. This kind of controller tries to eliminate difference between the object and predicting model by thinking the difference is due to gain difference and introducing a fuzzy controller. Simulation result shows that this kind of controller is valid to get satisfied control quality.FIBH method is a modification for conventional fuzzy control theory and structure. The main feature of this method is that history control data of time-delay system is taken into consideration of output decision. Simulation result shows that this method can improve dynamic and static characteristic of time-delay system control process and can get better result than conventional fuzzy controller.