Gain adaptation and compensation for deadtime processes with on-line applications to a heat exchanger

Abstract

The proposed gain adaptive deadtime compensation (GADC) algorithm and observer forms of compensation are developed for controlling a process with deadtime and varying characteristics. The GADC algorithm utilizes a gain adaptor to detect variations caused by changes in process characteristics and automatically compensates for these changes. The observer form of compensation employs a model to produce an estimated output along with a model controller to drive the deviation between the process response and estimated output to zero. Simulations were implemented with a digital computer to test the utility of these control algorithms for first and second order process. Frequency response analysis is used for providing the initial specifications of the parameters for the gain adaptor and model controller. The GADC algorithm and observer forms of compensation are shown to be superior to the simple PI control and the Smith method for controlling processes when a drastic process static gain change and small process time constant and deadtime changes occur simultaneously. These proposed control algorithms were also tested for actual "on-line" control of an industrial size heat exchanger with first and second order plus deadtime reference models. The main tests are for step decrease in coolant (water) flow rate. The decrease in water flow rate causes the process gain to change in combination with deadtime and time constant changes. However, the GADC algorithm and observer forms of compensation provide convergent and stable responses for the controlled outlet water temperature as the water flow rate decreases....