Base on All-pole Approximation a New Internal Model PID Control Method for the System with Time Delays

Nowadays IMC-PID is widely used in industrial field, but time delay problem is an unavoidable problem existing in IMC-PID design. First order Pade approximation, second order symmetric Pade approximation and second asymmetric Pade approximation are usually adopted to approximate time delay item, but these three approximation methods may bring zero-points to the system during approximation, and bring new pole-points to IMC-PID design, especially when they are used in second order process with time delay or high-order process with time delay, the calculation is quite complicated. In order to solve these problems, based on All-pole approximation, an new IMC-PID control method was proposed for the system with time delay. By using McLaughlin expansion, a general calculation formula of IMC-PID controller parameters was deduced. This new approach has advantages of few control parameters, slight overshoot, quick response, and it can be used in the system with great tau/T (delay time/time constant).