Phase and gain margins

I am seleeting the bandwidth of the elosed loop (fxo) power supply to be 6 kHz. It eould be as high as 15 to 20 kHz, but there is a double pole at one-half the switehing frequency which, if approached too closely, would ruin the phase and gain margin of the closed loop. 

The Bode plot of is given in Fig. 13.20 for D = 0.5. The ultimate gain is 3.9 (11.6 dB), and the ultimate frequency is 3.7 radians per minute. The ZN controller settings for P and PI controllers and the corresponding phase and gain margins and log moduli are shown in Table 13.2 for several values of deadtime D. Also shown are the values for a proportional controller that give +2-dB maximum closedloop log modulus. 

The phase and gain margins were measured using an average model of the SG1524 buck regulator. The schematic of the average model is shown in Fig. 4.34. 

Figure 4.57 Simulated low drop-out regulator phase and gain margins. Note the...

IV.64 Compute the phase and gain margins for the feedback systems with the open-loop transfer functions given in Problem IV. 58. On the basis of these values, find which systems are stable and which are not. 

Define the phase and gain margins and show how you can compute them from Bode or Nyquist plots. 

Explain in your own words what we mean when we say that phase and gain margins constitute safety margins (safety factors) in tuning a feedback controller. Why do we need a safety margin in tuning a feedback controller ... 

The discussion in Section 18.2 and Examples 18.2 and 18.3 has indicated that we could use very large phase and gain margins to guarantee closed-... 

Determine graphically the phase and gain margins wfren these settings are used. 

The specification of phase and gain margins requires a compromise between performance and robustness. In general, large values of GM and PM correspond to sluggish closed-loop responses, whereas smaller values result in less sluggish, more oscillatory responses. The... 

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