Research And Application Of Advanced Control Strategy In Power Plant Thermal Processes

Advanced DCS (Distributed Control Systems) have been used in large scale thermal dynamic facility's automatic control system. It provides good conditions for the application of the advanced control theory. However, because almost all of the large scale thermal facilities are still using conventional linear PID control system, it is very difficult to acquire excellent controlling performance in the global load varying range. Almost all of the critical control systems of the large scale power plant cannot acquire satisfying control quality when unit load varies in great ranges, it threatens the secure and economical operation of thermal dynamic facility severely.Most of the reheat steam temperature and superheat steam temperature control systems are the common cascade control system. But many of the controlled objects have large inertia and lag characteristic, and the spray valve have great nonlinearity. The steam temperature will deviate 8～10℃from the set-point when unit load changes, and always exceeds the steam temperature limits. Because the steam temperature usually exceeds the setpoint, the accident of blowing out the pipeline happened frequently. It threatens the unit's security and economy severely. So it is necessary to research new style steam temperature control strategy based on the modern control theory.Load system of the large scale power plant's unit as well, is a multi-variable nonlinear dynamic system, and the dynamic characteristic will change with the different operating condition. The traditional boiler-turbine coordinated control system is based on PID. This kind of coordinated control system is designed on a specific load condition. When the unit load varies in a large range, the unit's characteristic would also change significantly. The characteristic of the unit's load system has great nonlinearity, so it is impossible that the common PID control system have the global optimization in the whole load varying range. And it is difficult that the unit load tracking ability and the unit's stability have good control performance.Because the PID controlling law is linear while the controlled object is nonlinear, if we still use the traditional PID control theory to optimize the thermal power plant control system, we are using the linear controller to control the nonlinear object. Then the control performance would be confined. In order to improve the control performance, we must change the conventional control strategy thoroughly. We can research the global nonlinear optimizing control system which based on the power plant's global nonlinear model.In order to resolve the practical problem in the thermal process control of power plant, aimed at the large inertia and lag characteristics of the steam temperature object, and the time-variant and nonlinearity of the load system, combine with the nonlinear fuzzy model and predictive control, state variable control methods, this paper put forwards a series of advanced control strategies based on nonlinear fuzzy model state variable control theory, state feedback control theory and predictive control theory. It is a new idea for the controlling of the complex thermal-dynamical systems.The purpose of the selected researching aspect and the background of this paper are introduced in the first part of the paper. It also introduces the researching status of the state variable control, predictive control and Linear Matrix Inequality, and analyzes the existing...