Double First-Order Plus Time Delay Models to Tune Proportional-Integral Controllers

The first-order plus time delay (FOPTD) model-based method is a standard approach to tune proportional-integral (PI) controllers in plants. The FOPTD model can be obtained easily from step responses. However, because of their structural limitations, FOPTD models suffer from difficulties in approximating step responses for some processes including processes with overshoot, resulting in PI controllers with unacceptable performance. To remove these drawbacks, models combining two FOPTD models that can be obtained easily from step responses are proposed to tune PI controllers. Several simulations and experimental examples are given, illustrating the improved performance of the proposed method.