effect of addition of poles and zeroes

[mahe]

addition of poles in a system

In control system what is the effect of addition of poles and zeroes in stability

 

[vcrl82]

addition of poles and zeroes

if the poles and zeros lie inside the unit circle the system is said to be stable,
if it lies on the unit circle it is said to be marginally stable
if it lies outside the unit circle it is said to be unstable

 

[sridhara]

addition of poles

when a zero is added...the root locus of the system ...moves to left of s=jw plane...hence stability increases....
when a pole is added the root locus of the system moves closer to s=jw plane...(assuming pole is not added far away from origin.....)hence stability decreases.....
any control system book can be referred for detail if necessary

 

[vcrl82]

try reading CONTROL SYSTEMS BY GOYAL and bakshi ..................MORE THAN SUFFICIENT

 

[cesare]

Poles and zeroes introduce phase shift frequency dependant. So at some frequencies the negative feedback can turn to positive feedback

 

[laktronics]

Hi,
From a Bode plot point of view, each pole will roll off the gain at the rate of -6 db per octave and give a phase lag of max.90°, at corner frequencies the gain falls by 3db and the phase will be - 45°. A zero works as a complement of pole in that it provides a phase lead of max. 90° and a gain increase rate of +6 db per octave. In a closed loop control system if you plot Aβ and phase ange vs frequency in a single chart, then in the region of Aβ≥1, if the phase angle is kept below 180°, the system will be stable, the amount of stability depends on the phase margin of the system from 180°. The phase margin is especially critical at the point when Aβ=1, low phase margin at this point will easily tend to make the system unstable. Compared to Bode plot, root locus plot is considered better to assess stability of a system.
Regards,
Laktronics