Distributing PID controllers applied in water-mixing process

Abstract

In a process control system influenced by several parameters, which are usually located and separated in a large area, the one-central controller is not effective anymore. It is computationally hard for the controller hardware to do many tasks at the same time, therefore, they are considered to distribute in Local Control Units (LCUs). This research investigates the distributed PID controllers in the water-mixing process. The main controlled variables (SVG) are the level and temperature influenced by three parameters (flow-in of cold water, flow-in of hot water, and flow-out of the main tank), which are then distributed to LCU-1 to LCU-3. To maintain the SVG, the master controller is then designed based on the difference between SVG and feedback of the main-tank (PVG) so that it will deliver SV for each LCU. The results show that with control parameters in LCU-1 (Kp, Ti, Td are 2, 10, 0.46, respectively), LCU-2 (Kp, Ti, Td are 8, 6, 0.6), and LCU-3 (Kp, Ti, Td are 3, 70, 20), the response of water temperature (measured based on settling-time [Ts], % overshoot [OS], and rise-time [Tr]) are 42s, 0%, 45.3s. In the water level control, the response can be maintained with the 60s, 0%, 62s, for Ts, %OS, Tr, respectively.