PID controller tuning using Bode´s integrals

A new method for PID controller tuning based on Bode´s integrals is proposed. It is shown that the derivatives of amplitude and phase of a plant model with respect to frequency can be approximated by Bode´s integrals without any model of the plant. This information can be used to design a PID controller for slope adjustment of the Nyquist diagram and improve the closed-loop performance. Besides, the derivatives can be also employed to estimate the gradient and the Hessian of a frequency criterion in an iterative PID controller tuning method. The frequency criterion is defined as the sum of squared errors between the desired and measured gain margin, phase margin and crossover frequency. The method benefits from specific feedback relay tests to determine the gain margin, the phase margin and the crossover frequency of the closed-loop system. Simulation examples and experimental results illustrate the effectiveness and the simplicity of the proposed method to design and tune the PID controllers.