A study on the significance of backlash width values to the performance of the MIQP-based design of MPC

• Main Authors: H., Zabiri, Y., Samyudia
• Format: Conference or Workshop Item
• Published: 2005
• Subjects: TP Chemical technology
• Online Access: http://eprints.utp.edu.my/3767/1/haslinda_icis2005.pdf; http://eprints.utp.edu.my/3767/

One of the main contributors to the serious degradation in any control loop performance is the existence of actuator backlash. Most techniques in compensating the backlash effect includes the utilization of backlash nonlinear inverse, which is normally inserted prior to the control valves such that the net effect is a pure input/output gain. Though this technique proved efficient, one of the main disadvantages is when the control valve is operating near its saturation limits. As such, total compensation is not possible and the backlash effect may not be eliminated. An approach that has been recently developed involved the integration of the actuator backlash within the framework of Model Predictive Control (MPC) controller algorithm itself. This method, so-called the Mixed-Integer Quadratic Programming (MIQP)-based design of MPC, has been shown through extensive simulation on industrial case studies to be able to handle efficiently actuator saturation and actuator backlash nonlinearities simultaneously. In most cases, superior performance is achieved by the MIQP-based MPC in comparison to other existing backlash compensation methods. The simulation studies so far, however, assumed that the actual value of the backlash width is known exactly. In this paper, the performance of the MIQP-based MPC design is investigated against under- and over-estimation of the backlash width values. Simulation results via an industrial Fluidized Catalytic Cracking Unit (FCCU) case study are presented to show the significance of precise estimation of the backlash width in ensuring successful implementation of the MIQP-based design of MPC.