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Physical significance of zero (Read 13262 times)
adesign
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Re: Physical significance of zero
Reply #15 - Jan 23rd, 2007, 1:06am
 
Thank you Rajan, Bharat and Croaker for the detailed discussion!!

Best Regards,
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avlsi
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Re: Physical significance of zero
Reply #16 - Jan 23rd, 2007, 3:01am
 
Mr. Rajan,


I have a got a doubt. I have been taught all these days that RHP zero makes system unstable and not LHP zero.

Please clarify me on this.

I liked your practical explanation regaring poles and zeroes.

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Croaker
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Re: Physical significance of zero
Reply #17 - Jan 23rd, 2007, 7:44am
 
A RHZ has the same phase effect as a LHP.  So yes, it could degrade phase margin and make the system unstable.
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bharat
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Re: Physical significance of zero
Reply #18 - Jun 11th, 2007, 10:04pm
 
Thanks for your splendid explaination.
Still I want to ask;
Does this mean that differentiator response time is less as compared to integrator response time for the same unit step?


mg777 wrote on Jan 19th, 2007, 10:55am:
A zero represents differentiation of the input signal, while a pole integrates it. From a control theory perspective, a zero makes for a 'PD' controller which, like the proverbial hare, responds fast but with steady state error. OTOH a pole corresponds to a 'PI' controller that, like the tortoise, is slow to get there but does so with zero steady state error.

Here's a physical picture: say you're designing an elevator for a high rise building. You leverage a zero to get quick response but it won't do for the elevator to stop three feet short of the opening to a particular floor. Likewise you use poles for a slow but precise 'Driving Miss Daisy' ride that will align the door to the opening with millimetric precision (and leave passengers wishing they'd taken the stairs). The golden mean corresponds to a balance between haste and precision - it's called a PID controller and is non-trivial to design.

Non-linear circuits can be very different. A flip-flop regenerating its own input is like a snake chasing its tail. The unstable transient response takes off like a rocket, reaching steady state nirvana by saturating against one of the rails. If you design fighter aircraft you want 'em to whip around like that, but also not spin out of control or make Top Gun pass out. So you do an elaborate balance of linear and non-linear control. Even PID design is kid stuff compared to non-linear aircraft control amidst turbulence and countermeasures.

M.G.Rajan
www.eecalc.com




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