PID control is a very effective control method for industry and more than 95% of controllers for process control are of PID type. It is well-known that the performance of a PID controller depends on the tuning of its parameters. For this reason, a lot of tuning methods have been proposed.
Among them, predictive functional control (PFC) has appeared as a better choice to solve different problems. If the control objective is to improve the behavior of low-order processes, PFC is a good choice because of the simplicity of both algorithm calculation and tuning and its easy implementation and capability of constraints handling. In addition, PFC has many advantages over PID control. First, it can control time delay processes and constrain both the manipulated and controlled variables. Second, the tuning parameters have physical meaning, which is helpful for applying algorithms to practice. Therefore, if PID control and PFC are combined, better control performance can be achieved. In many papers, various design methods of PID controllers based on predictive functional control optimization are proposed. But these papers are focused on SISO systems and they do not cover MIMO systems.
Based on the principle of decoupling control, Kang Chung Hyok, a researcher at the Faculty of Metal Engineering, has proposed a new design method of PID controllers by PFC optimization for MIMO systems with time delay.
First, after decoupling, he divided the complex MIMO systems with time delay into independent subsystems. Then, he designed a PID controller based on PFC optimization after simplifying the subsystems into FOPDT models. The proposed controller not only inherits the advantages of PFC, but also has the same structure as a PID controller.
The simulation results show that the proposed controller has more improved control performance and better robustness than traditional PID controllers under the conditions of time delay and model/plant mismatches, and that the actuator’s life can be lengthened as the manipulated variable has no oscillating characteristics. In summary, the proposed controller can meet the requirements of complex industrial processes.
© 2021 Kim Chaek University of Technology