International Conference on Power Control and Optimization, Bali, Indonesia, 1-3, June 2009 THE EFFECT OF SIMULATED FEEDBACK ON THE STARTING DYNAMIC CHARACTERISTICS OF WATER PUMPING SYSTEMS WITH PLC CONTROL Salah Abdallah and Riyad Abu-Mallouh salahabdalah@asu.edu.jo , mallouh@maktoob.com Department of Mechanical and Industrial Engineering, Applied Science University, Amman 11931 Jordan. 1. Abstract In this work, PLC (Programmable Logic Controller) and frequency controlled water pumping system were modeled, designed and constructed. The open loop and simulated feedback control methods were employed, where the simulated feedback was suggested instead of real feedback. A test rig was built. An experimental study was performed to investigate the effect of using simulated negative feedback on the starting dynamic characteristics of water pumping systems driven by AC motor. From the analysis of the starting dynamic characteristics of water pumping systems with open loop control and with simulated feedback, it was noticed that, the systems with simulated feedback have clearly a better performance than systems with open loop control. Key Words: Simulated feedback, water pumping, PLC, frequency control, dynamic characteristics 2. Introduction Pumping equipment in the modern manufacturing systems may be used as main parts in many industrial activities, like chemical industries, food industries, etc. The use of modern control systems in these industries will certainly lead to improve there performance [Abdalah,2004]. Programmable logic controllers (PLC’s) present a vast improvement in capability and performance over other controllers. The rapid development in PLC technologies, which has allowed their applications to grow in size, was motivated by the progress of microelectronics and programming technologies [Mandado, 1996]. A number of studies used the PLC unit to control industrial processes [Abdalah, 2002a, 2002b and Kolokotsa, 2002]. Some of the studies used the frequency method of control, which depends on the existence of frequency inverter, to control three phase induction motor [Abdalah, 2004, Manz, 1997 and Jung, 1999]. There have been several research works aiming to develop the methods of controlling electrical motors driven centrifugal pumps, in order to improve their performance. From the analysis of the working conditions of water pumping systems, it can be seen that there are many problems, facing the work of such systems, such as hydraulic hummer, dynamic stresses in mechanical parts and high starting current in the three phase motor [Rossman,1998,Lingji,1996 and Kamalov,1994]. A large number of investigations have been conducted in theoretical design and mathematical modeling of induction motors with frequency control, [Abdalah,2002 and Kolokotsa,2002]. This study seeks to evaluate the effect of simulated feedback on the performance of starting dynamic characteristics in water pumping systems. In this work, the simulated feedback was suggested instead of real feedback. This would improve the performance of these systems especially during transient conditions. This would enable building such systems without using transducers or their co- elements. The simulated feedback represents a programmed negative feedback and not a real feedback, where the feedback values can be programmed and sent by PLC system. In this work, the electromechanical system “ PLC – Frequency inverter – Three phase induction motor – Centrifugal pump – Pipeline “ were modeled, designed, constructed and tested in two cases, first case, with open loop control, and second case with simulated feedback control. 3. Theoretical Model of Water Pumping System with PlC and Frequency Control: The mathematical description of water pumping system with PLC and frequency control will be based on the expressions given in [Manz, 1997, Jung, 1999, Lingji, 1996 and Kamalov, 1994]. A) Modeling of Electromagnetic Processes of Frequency Controlled AC Motor The main equations of common two phase wound rotor AC motor using coordinate system, rotating with random angular velocity ω k in vector form are: 1 1 1 1 k d u iR j dt ψ ωψ = + + (1) ( ) 2 2 2 2 0 k d iR j p dt ψ ω ωψ ′ = + + - (2) where: ω: The angular velocity of the rotor p: Number of pairs of poles ū, ī 1 and 1 ψ : The resulting vectors of voltage, current and magnetic flux of stator.