Temperature Control ofDeionized (DI)Water Heater byCombination ofPIDControl and ModernControl Theory

Combination ofproportional-integral-derivative (PID)control andmoderncontrol theory suchasobserver cancontrol moredifficult application thanPIDcontrol only. We proposed combined control technique ofPIDcontrol and disturbance observerforthetemperature controlof deionized (DI)waterheater thatisusedforsemiconductor processing equipment. Theresult ofbothsimulation and actualequipment experiment verified thattheproposed methodenabled notonlytousefewertemperature sensors thanconventional system thatleads toacostreduction but alsotohaverobustness against modeluncertainty ofalamp heater suchasa nonlinearity ofinput-output relationship, powervariation, andsuddenburnout.