the pe 2 feodbuck comer openating at a switching frequency, f-200 KHz, and suppo
ID: 2291173 • Letter: T
Question
the pe 2 feodbuck comer openating at a switching frequency, f-200 KHz, and suppose we wsh to design for this system. The Bode plot of the open loop transfer function, G,(s), of the PWM-switch-filter-load sections of the converter is shown in the following figure. Bode plot of Sw lich-Fher-Load transfer function, Go(s) 30 20 10 -10 -20 -30 G 45 -90 135 10 10 10 Frequency (rad/sec) a) What is the phase margin of the open loop system, G,(s)? b) Using your engineering judgment, please pick a new gain cross-over explain your choice frequency, O,and briefly c) Determine the extra gain and phase angle to be provided by the compensator, G(s), to realize a phase margin of 50Explanation / Answer
a) the crossover frequency is 40khz , at this frequency the phase is around -100 degrees therefore your phase margin is nearly 80 degrees which is quite good.
b)but the cross over frequency should be generally a decade less than switching frequency, this makes your system to track faster references as well the switching harmonics are not allowed to pass. therefore now the crossover frequency should be nearly 20 kHz, P.M here would be around 65-70 degrees which is still very good. Generally P.M above 60 degrees is good.
c) you dont need to provide any extra phase and all. your system already has 50+ P.M for any cut off frequency you want.
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