抄録
Almost all industrial plants have nonlinear properties. Therefore, when an output of the system is controlled to be constant, the equiliblium point is varied by the mean value of the unregulatable inputs (disturbances) and the system parameters. If the changes of the equiliblium points can be detected, they are useful information for setting of controllers to the linearlized system at the equilibrium point or for detecting the abnormalities of the system. In actual plants PID controllers are widely used for feedback controls and for feedforward controls to feedback controls. The reason for this is due to the ease of their parameter setting even in the case that the equilibrium points vary between some bounds. The adaptability of PID is principally depending on the effect of I-element used in a feedback controller.
In this paper one detection method of equilibrium changes is presented. This is based on the observation of the output value of an I-element in a PID controller used for set point control. For the two cases, one with known statistical properties of the disturbances and the other with real time observation of them, the properties of the proposed method are discussed. For the numerical example, some results obtained from the simulation of a rolling process of a steal mill are presented.
