Temperature Control of Deionized (DI) Water Heater by Combination of PID Control and Modern Control Theory

Combination of proportional-integral-derivative (PID) control and modern control theory such as observer can control more difficult application than PID control only. We proposed combined control technique of PID control and disturbance observer for the temperature control of deionized (DI) water heater that is used for semiconductor processing equipment. The result of both simulation and actual equipment experiment verified that the proposed method enabled not only to use fewer temperature sensors than conventional system that leads to a cost reduction but also to have robustness against model uncertainty of a lamp heater such as a nonlinearity of input-output relationship, power variation, and sudden burnout.