www.gusucode.com > control 案例程序 matlab源码代码 > control/UnityGainCrossoverExample.m

    %% Unity Gain Crossover  
% Find the 0dB crossover frequencies of a single-loop control system with plant given
% by:
% 
% $$G\left( s \right) = {1 \over {{{\left( {s + 1} \right)}^3}}},$$
% 
% and PI controller given by:
% 
% $$C\left( s \right) = 1.14 + {{0.454} \over s}.$$
% 
%%  
G = zpk([],[-1,-1,-1],1);
C = pid(1.14,0.454);
sys = G*C;
wc = getGainCrossover(sys,1) 

%%
% The 0 dB crossover frequencies are the frequencies at which the open-loop response
% |sys = G*C| has unity gain. Because this system only crosses unity gain
% once, |getGainCrossover| returns a single value.