Method for PID-tuning via feedback control system pole placement

Abstract

Pole placement is the only PID-tuning technic that allows one to obtain a control system with desired, and, moreover, highly predictable performance and control quality. Number of controller tuning parameters is equal to number of poles closed-loop poles it can precicely place, so that PID-controller can place exactly three poles, and PI- can place only two. For this reason PI-controller is best used with first-order processes (second-order closed loop system), and PID-controller with second-orded ones (third-order closed loop system). However, many processes have higher order than two, and still are controlled with PID-controllers. To tune it using pole placement techniques, it is necessary to consider only dominant poles, which affect performance of the system to the greatest extent. First, it is necessary to study a PI-controller with a second-order process, which is the most basic case. Tuning is performed using global optimization methods to fit dominant poles of a tuned system to dominant poles of a reference system.