Open-loop frequency response locus

The closer the open-loop frequency response locus G(ja )//(ja ) is to the (—l,j0) point, the nearer the closed-loop system is to instability. In practice, all control... 

The Nichols chart shown in Figure 6.26 is a rectangular plot of open-loop phase on the x-axis against open-loop modulus (dB) on the jr-axis. M and N contours are superimposed so that open-loop and closed-loop frequency response characteristics can be evaluated simultaneously. Like the Bode diagram, the effect of increasing the open-loop gain constant K is to move the open-loop frequency response locus in the y-direction. The Nichols chart is one of the most useful tools in frequency domain analysis. 

From Figure 6.27 it can be seen that the peak modulus Mp is 4dB, occurring at ujp = 1.63rad/s. The bandwidth is 2.2rad/s. For the best flatband response, the open-loop frequency response locus should follow the 0 dB M contour for as wide... 

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