Jaspreet nyquist Stability Flashcards

1
Q

When will a closed loop system be stable?

A

When the magnitude of G(s) < 1 and the angle = +- 180
OR
Magnitude = 1 and angle > -180

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2
Q

When will a closed loop system be marginally stable?

A

When Magnitude of G(s) = 1 and angle = 180

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3
Q

What do gain and phase margins tell us?

A

They tell us how stable a system is by defining how much variation we have in G(s) before the system comes unstable. It makes use of the Nyquist Stability criteria

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4
Q

What is Gain Margin (Kg)?

A

It is the change in open loop gain that is needed when the phase plot crosses -180 to make the system unstable.

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5
Q

What is Phase Margin(gamma)?

A

it is the change in open loop phase shift that is needed when the gain crosses 0 to make the system unstable.

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6
Q

What is the gain margin frequency?

A

it is the frequency at which the phase plot will cross the -180 degree line.

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7
Q

What is the phase margin frequency?

A

It is the frequency at which the gain plot will cross the 0db line.

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8
Q

If Kg > 0 and gamma > 0 then what does this mean for the stability?

A

The system will be stable when Kg > 0db and gamma > 0 degrees

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9
Q

If Kg < 0 and gamma < 0 then what does this mean for the stability of the system?

A

The system will be unstable when Kg < 0 and gamma < 0

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10
Q

How do we determine if the system is stable when Kg > 0 but gamma < 0 OR Kg < 0 but gamma > 0?

A

We have to resort to the Nyquist Criterion

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