MATLAB: Related to Matlab Step Comment

steady state error

Hello, I have some question about Step resoponse Comment,
once, I want to plot about open loop system only use Transfer function,
For example for 1/(s+3) sytem, when I plot,
G = tf(1, [1,3])
step(G)
then the Final value of step response is 0.333, So Steady – State error around 0.667
When calculate steadt-state error is fisrt ordher system, We use 1/(1+Kp),
So in this system, Kp = 1/3, So Ess have to be 0.75.
Why is that differenet ??

Best Answer

You are possibly confusing the closed loop response with the open loop. The closed loop gain is 1/4, so the error is 1-1/4 = 3/4. 
>> Gcl = feedback(G,1);
>> step(Gcl)
>> dcgain(Gcl)
ans =
    0.2500
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