Designing and Testing of Modern Tools for Control Systems Prototyping

The main contribution of this paper is the use of a new tuning rule that gives a new relationship for PID controller in stead the modified Ziegler-Nichols method. We propose to add an extra condition that the phase Bode plot at a specified frequency w_c at the point where sensitivity circle touches Nyquist curve is locally flat which implies that the system will be more robust to gain variations. Several relay feedback tests used to identify the plant gain and phase at the tangent frequency in an iterative way. The identified plant gain and phase at the desired tangent frequency used to estimate the derivatives of amplitude and phase of the plant with respect to frequency at the same frequency point by Bode's integral relationship. No plant model assumed during the PID controller design. Only several relay tests needed. Experimental results with DC motor illustrate the effectiveness.