pgpi

  PGPI(NUM,DEN,W,FI,A) plots the stability boundary locus L(KP,KI,W)in the (KP,KI)-plane for an LTI system with transfer function defined by its NUM, DEN coefficients and driven by a PI controller with transfer function, C(s)=kp+(ki/s). Frequency (W) gridding becomes important. Phase Margin, FI, and Gain Margin, A, can be defined. The method works for open loop stable or unstable, minimum or nonminimum phase systems. With Examples. Method and examples used are form "Computation of Stabilizing PI and PID Controllers" by Nusret Tan, Ibrahim Kaya and Dereck P. Atherton. MATLAB release MATLAB 7.5 (R2007b)