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From what I have studied so far, gain margin is defined as how much additional gain the system can be given before it becomes unstable, and this can be measured from the bode magnitude plot corresponding to the frequency at which the phase crosses -180 degrees.

  • What if the phase plot is such that it becomes flat-looking at say -75 degrees, and never goes below that? Then how is the gain margin calculated? (i.e then will the phase crossover frequency be infinite?)

  • If an open loop system's bode plot says that it has negative gain margin but positive phase margin, is the system unstable (and cannot be stabilized)?

EDIT: How would the -180 degree phase crossover frequency point be determined here? For example, just by a Google search I got a few instances,

  1. Paper1 enter image description here

  2. Paper 2 Boost

From what I have studied so far, gain margin is defined as how much additional gain the system can be given before it becomes unstable, and this can be measured from the bode magnitude plot corresponding to the frequency at which the phase crosses -180 degrees.

  • What if the phase plot is such that it becomes flat-looking at say -75 degrees, and never goes below that? Then how is the gain margin calculated? (i.e then will the phase crossover frequency be infinite?)

  • If an open loop system's bode plot says that it has negative gain margin but positive phase margin, is the system unstable (and cannot be stabilized)?

From what I have studied so far, gain margin is defined as how much additional gain the system can be given before it becomes unstable, and this can be measured from the bode magnitude plot corresponding to the frequency at which the phase crosses -180 degrees.

  • What if the phase plot is such that it becomes flat-looking at say -75 degrees, and never goes below that? Then how is the gain margin calculated? (i.e then will the phase crossover frequency be infinite?)

  • If an open loop system's bode plot says that it has negative gain margin but positive phase margin, is the system unstable (and cannot be stabilized)?

EDIT: How would the -180 degree phase crossover frequency point be determined here? For example, just by a Google search I got a few instances,

  1. Paper1 enter image description here

  2. Paper 2 Boost

Source Link
SM32
SM32
  • 450
  • 4
  • 19

Bode phase plot phase margin

From what I have studied so far, gain margin is defined as how much additional gain the system can be given before it becomes unstable, and this can be measured from the bode magnitude plot corresponding to the frequency at which the phase crosses -180 degrees.

  • What if the phase plot is such that it becomes flat-looking at say -75 degrees, and never goes below that? Then how is the gain margin calculated? (i.e then will the phase crossover frequency be infinite?)

  • If an open loop system's bode plot says that it has negative gain margin but positive phase margin, is the system unstable (and cannot be stabilized)?