Shaunak Chakrabartty et al Int. Journal of Engineering Research and Applications www.ijera.com ISSN : 2248-9622, Vol. 4, Issue 5( Version 5), May 2014, pp.13-18 www.ijera.com 13 | Page Performance Analysis Of Various Anti-Reset Windup Algorithms For A Flow Process Station Shaunak Chakrabartty 1 , Dr.I.Thirunavukkarasu 2 And Mukul Kumar Shahi 3 1 Department of Instrumentation and Control Engg., Manipal Institute of Technology, Manipal, Karnataka, India, 2 Associate Professor, Department of Instrumentation and Control Engg., Manipal Institute of Technology, Manipal University, Manipal-576104, Karnataka, India. 3 Department of Instrumentation and Control Engg., Manipal Institute of Technology, Manipal, Karnataka, India, Abstract The study was aimed to develop the various aspects of Anti reset windup or Integral windup and also the different algorithms available to eliminate the phenomenon of windup. Different open loop responses were obtained from a Flow process Station using MATLAB and SIMULINK and VI Microsystems process control software. The open loop responses were evaluated and different system models were generated using the two point method. The system models were found to follow a decreasing order of Gain values and an increasing order of T d and T values. A SIMULINK model was obtained to implement Back calculation combined with Conditional Integration. The models for the system obtained were simulated using the SIMULINK model and a PID controller and the closed loop responses were generated. The closed loop responses using a PID controller with Back calculation and Conditional integration were found to follow the set point as expected. Keywords—Anti reset windup, Integral windup, back-calculation, conditional integration, flow process, tracking time constant, PID controller, SIMULINK. I. INTRODUCTION In practice all control loops and processes contain nonlinearities. Examples are saturation in actuators, gain or parameter variations due to changes in operating point of the process, and backlashes in valves and gears. The influence of nonlinearities is often eliminated by keeping the process close to a desired operating point. A linearized model is then often valid and can be used for the design of the controller. A control system which operates over a wide range of operating conditions, windup phenomena may happen as the manipulated variable reaches the actuator limits. When windup happens the feedback loop is assumed as broken and the system runs in open loop because the actuator will lock in saturation as its limit independent of the error dynamics. The controller output then becomes very large. The control signal then remains saturated even the error changes its direction and it may take a long time before the integrator and the controller output comes inside the saturation range. The consequence is that there are large transients. Generally when a large set point change is given and the PID controller produces a control signal (as the integral of the larger error) which the maximal effort is taken by the controller for regulation of the process variable. Then the control signal lets the actuator immediately go to its saturation limits, thus the process variable overshoots and continues to increase as this error being accumulated by the controller itself. This is known as Integral Windup in control systems. The project aims at eliminating windup problem using various techniques available in literature. II. ANTI RESET WINDUP Bohn. C, and D.P. Atherton [3], represented additional actuator dynamics rather than the saturation in the first position of system to be controlled. A lower limit for the actuator output leads to higher integrator output and higher settling time. The effect of integrator windup can be explained by the fact that when the control signal saturates the actuator, a further increase of the control signal will not lead to a faster response of the system. If integration of error continues in this case it becomes very large compared to the linear system it winds up, without having any effect on the plant output. The control error then has to be of the opposite sign for a long time to bring the integrator back to its steady state value. This results in a large overshoot and a high settling time. In order to effectively employ a PID controller in practical cases, implementation of some additional functionalities are needed. The derivative action is often applied directly to the process variable instead of to the error in order to avoid the so-called derivative kick when a step signal is applied to the set-point. Suitable techniques should be implemented properly in order to avoid the windup effect of the RESEARCH ARTICLE OPEN ACCESS