StepInfo Outputting NaN for my Transfer Function

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Omar
Omar 2011-9-16
I am trying to find the overshoot of a transfer function for a step response but the stepinfo command does not display anything useful. This is the code.
sys=tf(280*[1 1.5 .5], [100 215 30.5 1 0]);
stepinfo(sys)
ans =
RiseTime: NaN
SettlingTime: NaN
SettlingMin: NaN
SettlingMax: NaN
Overshoot: NaN
Undershoot: NaN
Peak: Inf
PeakTime: Inf

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回答（2 个）

Fangjun Jiang
Fangjun Jiang 2011-9-16
a=step(sys);
b=stepinfo(a)
Craig
Craig 2011-11-18
Hi Omar,
The system you specified has an integrator and is therefore unstable. This is the reason why NaN's are being returned by stepinfo.
You can see the response by doing
>> step(sys)
-craig
  1 个评论
Fangjun Jiang
Fangjun Jiang 2011-11-19
That is the point of my answer. It needs to run step() first to get the step response and then run stepinfo() using the step response as the input.
The existence of an integrator in the system increases the chance of making the system stable. It's usually the derivative that makes the system un-stable.

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