QUICKTUNE - A RELIABLE AUTOMATIC STRATEGY FOR DETERMINING PI AND PPI CONTROLLER PARAMETERS USING A FOPDT MODEL

It is well known that many complex processes are often satisfactorily controlled by means of simple two-term (PI) and three-term (PID) contr ollers. However, for those processes which use PI and PID loops, the t ask of 'tuning' can be a very time-consuming and expensive operation. Consequently, any help offered to the process operator to ease this te dious task and at the same time produce consistent behaviour is very d esirable. This paper presents a CAD software package that automaticall y determines the necessary PI parameters for two-term operation, ident ifies those situations where PI is not appropriate, and in these cases designs an alternative pPI strategy. The original software used the Z iegler-Nichols empirical settings, but this paper considers a range of options which (in theory) should realise a less oscillatory response. All of the strategies considered are based on a first-order-plus-dead time (FOPDT) plant model. The paper also introduces a new set of tunin g relationships which, despite their simplicity, appear to realise a c onsistent, sensibly damped step response, much superior to the Ziegler -Nichols values. The paper concludes by considering two 'real applicat ions', namely, flow and pH control, which illustrate the quality of th e performance achievable using the CAD software. Copyright (C) 1997 El sevier Science Ltd.