Online Tuning of PI Controller for Spherical Tank System Using Root Locus Technique with Regulatory Operation

The closed-loop control system plays an important role in modern process control industries. Many challenging control problems arise in the chemical process industries, due to nonlinear dynamic behavior, uncertainty time varying parameters, unmeasured frequency disturbance and dead time. In chemical process industries, the control of water level for a spherical tank system (STS) is a difficult task, due to variations present in the cross sectional area with respect to height. The research work, the entire operating region of STS is categorized into three approximate linear regions and their open-loop responses transfer function models are derived by using the process reaction curve method. The Proportional Integral (PI) controller has been designed to control the water level in the spherical tank system. The PI controller parameters are tuned by using the conventional Ziegler-Nichols Tuning (ZNT) method and proposed Root Locus Technique (RLT). The real-time experimental regulatory responses of the STS for PI controller parameter tuned by ZNT method and RLT are compared based on performance indices such as IAE and ISE.