Interpret disk gain and phase margins

dmplot dmplot(diskgm)

`[dgm,dpm] = dmplot`

`dmplot`

brings up a plot
that illustrates the disk gain margin (`dgm`

) and
disk phase margin (`dpm`

) for a sample system. Both
margins are derived from the largest disk that

Contains the critical point (–1,0)

Does not intersect the Nyquist plot of the open-loop response

*L*

`diskgm`

is the radius of this disk and a lower
bound on the classical gain margin.

`dmplot(diskgm)`

plots the
maximum allowable phase variation as a function of the actual gain
variation for a given disk gain margin `diskgm`

(the
maximum gain variation being `diskgm`

). The closed-loop
system is guaranteed to remain stable for all combined gain/phase
variations inside the plotted ellipse.

`[dgm,dpm] = dmplot`

returns
the data used to plot the gain/phase variation ellipse.

Barrett, M.F., Conservatism with robustness tests for linear feedback control systems, Ph.D. Thesis. Control Science and Dynamical Systems, University of Minnesota, 1980.

Blight, J.D., R.L. Dailey, and Gangsass, D., "Practical
control law design for aircraft using multivariable techniques," *International
Journal of Control*, Vol. 59, No. 1, 1994, 93-137.

Bates, D., and I. Postlethwaite, Robust Multivariable Control of Aerospace Systems, Delft University Press, Delft, The Netherlands, ISBN: 90-407-2317-6, 2002.

Was this topic helpful?