Identification of ill-conditioned process using closed-loop data

An ill-conditioned process is one in which there exists equipment with unmeasurable variables between the input and output data to be modeled. The identification of closed-loop systems is investigated using actual closed-loop data. Optimization calculation techniques are used to identify the closed-loop system, and the small gain theorem is used to verify the model. The targeted control loop is the temperature control loop of a TW303 distillation tower. The only measurable process variable which greatly affects the TW303 bottom temperature is the reboiler flow rate. Hence, input and output variables of the heat exchanger cannot be measured. The temperature and reboiler flow rate data has a periodic oscillation of 12 minutes. Even though the periodic oscillation is caused by the equipment, the controllers must be able to control any type of disturbance. We investigate the cause of these problems by focusing on poor PID settings