A PLC-based system for advanced control

Abstract

The chapter presents a PLC-based system for advanced control called ASPECT. The ASPECT controller was designed to be an efficient and user-friendly engineering tool for the implementation of parameter-scheduling nonlinear control in the process industry, which is achieved by partial automation of the commissioning procedure. The key to the concept is the self-tuning mechanism. The controller parameters are automatically tuned from a nonlinear process model. The model is determined on the basis of operating process signals by experimental modelling, where an online-learning procedure is used. This procedure is based on model identification using the local learning approach. The two main components of the ASPECT system are the Run-time Module (RTM) and the Configuration Tool (CT). The RTM runs on a PLC or an embedded controller, performing all the main functionality of real-time control, online learning, and control performance monitoring. The CT, used on a personal computer (PC) only during the initial configuration phase, simplifies the commissioning procedure by providing guidance and default parameter values. The performance of the system is demonstrated with simulation experiments on a pH control process and with experimental application to an industrial valve-testing apparatus. In the conclusion, the lessons learned during the development and implementation of the system are discussed.