Blog for students taking ECEN5807 Modeling and Control of Power Electronics, ECEE Department, University of Colorado at Boulder, Spring 2013
Wednesday, March 23, 2011
HW8 Prob 2
At the risk of coming across as a simpleton, how do you go about calculating the steady state duty cycle for differing loads in part a? Every time I try a different approach I come up with the same duty cycle for all loads which cannot be the case.
I think you are correct when you calculate identical D for different load currents. D determines the DC voltage conversion ratio for a buck converter, this is no different in CPM, even at different load currents. What changes with the load current is the DC current through the inductor. The ripple current is determined by D, L, Vg, V and Ts; all should also remain the same in steady state, if the output voltage is regulated to the correct value. d_hat will be non-zero during transients to facilitate build up/down of the inductor current as the load current changes.
I think you are correct when you calculate identical D for different load currents. D determines the DC voltage conversion ratio for a buck converter, this is no different in CPM, even at different load currents. What changes with the load current is the DC current through the inductor. The ripple current is determined by D, L, Vg, V and Ts; all should also remain the same in steady state, if the output voltage is regulated to the correct value. d_hat will be non-zero during transients to facilitate build up/down of the inductor current as the load current changes.
ReplyDeleteI agree with Toby. I would also add that D does not depend on the load resistance in CCM; however, it does, in DCM.
ReplyDeleteThanks guys.
ReplyDelete