Whats the zero compensation effect and theory?

about zero

please,the zero compensation's effect,and theory?

Re: about zero

Ur doubt is not clear.

Re: about zero

in a feedback system,Why we add a zero.what effect of the zero.such as increasing the bandwidth or reponse rate? how does the zero function?

Re: about zero

usually adding a zero in order to increase the phase margin of feedback system.

Re: about zero

Hi:

If the feedback can creat a zero on the left half plane in the s domain, it can be used to cancel some poles, therefore to reduce the overall phase margin to increase the stability of the circuit.

J

Re: about zero

Jenifer_gao said:

Hi:

If the feedback can creat a zero on the left half plane in the s domain, it can be used to cancel some poles, therefore to reduce the overall phase margin to increase the stability of the circuit.

J

Click to expand...

hi J,
how can it be "reduce the overall phase margin to increase the stability of the circuit" ?
I think it should be increasing the overall phase margin to increase the stability of the circuit.

about zero

hi,
-jw is 90 phase margin,jw is -90 phase margin,so left plane zero is reverse to pole,so it can reduce phase margin.rignt?
like that,can we use a zero cancel the dominate pole to boarden bandwidth

Re: about zero

huangjw said:

hi,
-jw is 90 phase margin,jw is -90 phase margin,so left plane zero is reverse to pole,so it can reduce phase margin.rignt?
like that,can we use a zero cancel the dominate pole to boarden bandwidth

Click to expand...

Phase Margin (PM)= ΦH(jωu)-(-180°)=180°+ΦH(jωu),
(1)add a LHP zero in H(jw) , u will get PM=180+Φ[H(jwu)*(jwu/ωz+1)]=180+Φ[H(jwu)]+90°, if wu >> wz, where wu is the unity gain bandwidth
(2)add a RHP zero in H(jw) , u will get PM=180+Φ[H(jwu)*(jwu/ωz-1)]=180+Φ[H(jwu)]-90°, if wu >> wz

so (1) will increase PM, (2) will decrease PM

Re: about zero

Btrend said:

huangjw said:

hi,
-jw is 90 phase margin,jw is -90 phase margin,so left plane zero is reverse to pole,so it can reduce phase margin.rignt?
like that,can we use a zero cancel the dominate pole to boarden bandwidth

Click to expand...

Phase Margin (PM)= ΦH(jωu)-(-180°)=180°+ΦH(jωu),
(1)add a LHP zero in H(jw) , u will get PM=180+Φ[H(jwu)*(jwu/ωz+1)]=180+Φ[H(jwu)]+90°, if wu >> wz, where wu is the unity gain bandwidth
(2)add a RHP zero in H(jw) , u will get PM=180+Φ[H(jwu)*(jwu/ωz-1)]=180+Φ[H(jwu)]-90°, if wu >> wz

so (1) will increase PM, (2) will decrease PM

Click to expand...

I think is's better to use the following way to understand the pole and zero. Considering a transfer function with one zero and pole:

H(s) = Ao(1+s/ωz)/(1+s/ωp), we say this transfer function has a zero at the left half plane, because when the nominator equals to 0, we can get s = -ωz, and we say this transfer function has a pole at the left half plane, because when s = -ωp, the dominator will be 0. But when we calcualte the phase margin, we have to convert this H(s) to the following form:
H(s) = Ao(1+s/ωz)(1-s/ωp)/(1+(s/ωp)^2)
the term of (1+s/ωz) will result in a postive phase, but the term of (1-s/ωp) will lead to a negative phase, so these two can be used to cancel each other. For the right half plane zero, it has the form of (1-s/ωz), which will give a negative phase, therefore will worse the stability. Hope I explain it clearly.

J

Re: about zero

zero eliminate pole to get pm