Abstract
With the recent structural change of electric power supply and demand system, designers of thermal power plants have put much emphasis on their control characteristics such as quick startup and load following in a middle load operation.
In general, fast transient operations tend to speed up life consumption of a turbine rotor metal due to thermal stresses. It is one of the most important subjects for a designer of turbine control systems to reduce the time required for startup and load following. From a viewpoint of the control theory, this kind of subject falls on the minimum-time control problem with constraints in process variables and controls. But it is extremely hard to find real time optimum controls for the processes that have a large degree of nonlinearities and many state variables.
We developed a new computer control method for a turbine with which the following functions are provided.
(1) an estimation of boiler outlet steam conditions by means of autoregressive modeles.
(2) a prediction of turbine inner steam conditions, heat transfer coefficients of rotor surface, and thermal stresses, based on the estimated steam conditions.
(3) a minimization of the time required for startup and load following by determining the desirable rate of speedup and load variation.
And we evaluated the control characteristics of the newly developed method through computer simulations. The results showed a high accuracy of stress control within allowable limits, and proved that the method will reduce the startup time by 25% and the load following time by 30% compared with a conventional off-line scheduled control method. The control system may answer a need of future power plants for safety and high reliability.
