
282 Shipboard Electrical Power Systems
11.4.2 Parallel resonanCe with soUrCe
A concern in placing the pf improvement capacitor C
pf
is the parallel resonance with
the Thevenin source inductance L
source
at natural undamped resonance frequency
f
L C
r
source pf
=
1
2π
Hz
(11.15)
On a bus with a power electronics load drawing harmonic currents, this concern is
amplied if any of the current harmonic frequencies match with this resonance fre-
quency. For example, the 6-pulse power electronics converter draws harmonic cur-
rents of the order 5, 7, 11, 13 …, which have frequencies 300, 420, 660, 780 …Hz,
respectively, in 60 Hz systems. If the resonance f