Studies on fractional order control system

Abstract

A tank is an important unit of almost all chemical process industries. newlineAn ideal tank should occupy less space for a definite volume and should be newlineable to drain all the stored material when ever needed. A spherical tank is a newlinegood choice which will satisfy both of the above requirements because of its newlinestructure. So many of the process industries use spherical tanks as storage newlinetanks of cryogenic liquids, fuels and other liquids and as surge tanks between newlinetwo consecutive stages of processes. newlineIn many processes the liquid will undergo either a chemical or newlinemixing treatment in the tanks. Due to gravity, liquid settles down in these newlinetanks where because of presence of different rates of inlet and outlet streams newlinethe height of stored liquid changes with time. A too high level may upset newlinereaction equilibria, cause damage to equipment or result in spillage of newlinevaluable or hazardous material. A too low level may have bad consequences for the sequential operations. Hence control of liquid level is an important and newlinecommon task in process industries. newlineControl of liquid level in a spherical tank is a challenging problem newlinebecause of its nonlinearity due to the variation in the area of cross section. newlineHence, the spherical tank process is taken up for study here. Most of the newlinechemical processes exhibit an open loop response which can be approximated by a first order system with dead time. In this research work, first the newlinespherical tank is modeled as first order plus dead time (FOPDT) system about newlinedifferent operating points. Dead time is a principal source of destabilizing newlineeffects in chemical process control systems. It is clear that the possibility for newlineclosed loop instability will almost and always be present. Therefore the newlineselection and tuning of feedback controller becomes a crucial task. In this newlineresearch work instead of conventional feedback controller fractional newlinecontrollers are designed for the rationalized FOPDT models. Fractional order PI and fractional order PID controllers are designed newlinefor the developed FOPDT models. newline newline