Input filter design for CPM controlled converters

• Reference paper:

Y.Jang, R.W.Erickson, "Physical origins of input filter oscillations in current programmed converters," IEEE Transactions on Power Electronics, Vol.7, No.5, Oct.1992.

Physical origins of input-filter oscillations

Design objective: Gvc should not be affected by the input filter:

• Effects of input filter on Gvd

• Effects of input filter on Gid

• Additional “feed-forward” loop though vg

Effects of input filter on Gvd

Effects of input filter on Gid

Additional loop through vg

Additional loop through vg

Computation of Ggd

Effects of Ggd

vFvFGiGF

Fd vggigcidm

m ˆˆˆ1

ˆ

Design objective: Gvc should not be affected by the input filter:

• Effects of input filter on Gvd

• Effects of input filter on Gid

• Additional “feed-forward” loop though vg

Design criteria

Do ZZ No ZZ

Nfo ZZ

Typical buck converter impedance criteria (see the reference paper)

Experimental example (see the reference paper)

Input filter oscillations: ZN and ZD

L=2.5mH

Ma=3 M2

D=0.35

R=10

L=0.275mH

Ma=0

D=0.47

R=25

Close to DCM

Input filter oscillations: ZNf