Control System Toolbox™

allmargin

All crossover frequencies and corresponding stability margins

Syntax

S = allmargin(sys)
s = allmargin(mag,phase,w,ts)

Description

S = allmargin(sys)

allmargin computes the gain, phase, and delay margins and the corresponding crossover frequencies of the SISO open-loop model sys. allmargin is applicable to any SISO model, including models with delays.

The output S is a structure with the following fields:

• GMFrequency — All -180 degree crossover frequencies (in rad/s)

• GainMargin — Corresponding gain margins, defined as 1/G where G is the gain at crossover

• PMFrequency — All 0 dB crossover frequencies in rad/s

• PhaseMargin — Corresponding phase margins in degrees

• DMFrequency and DelayMargin — Critical frequencies and the corresponding delay margins. Delay margins are given in seconds for continuous-time systems and multiples of the sample time for discrete-time systems.

• Stable — 1 if the nominal closed-loop system is stable, 0 otherwise.

In general, stability cannot be assessed for FRD system. In any case when stability cannot be assessed, S is set to NaN.

s = allmargin(mag,phase,w,ts) computes the stability margins from the frequency response data mag, phase, w, and the sampling time, ts. allmargin expects frequency values w in rad/s, magnitude values mag in linear scale, and phase values phase in degrees. Interpolation is used between frequency points to approximate the true stability margins.

See Also

ltimodels, ltiview, margin

acker

append