IEEE Electrification Magazine - December 2013 - 50

f
CC

MCC
t

(a)

(b)

Figure 3. The Li-ion battery charging techniques: (a) CC-CV and (b)
MCC-CV.

(a)

the typical power architecture of an oBc is shown in
Figure 5. typically, an isolated oBc consists of two stages:
1) the first stage for ac/dc conversion and power factor
correction (pFc) and 2) the second stage for dc/dc conversion and galvanic isolation.
the first-stage ac/dc pFc converter typically consists of
an electromagnetic interference (eMi) input filter, rectifier,
pFc converter, and dc link capacitor.
the pFc converter is controlled by a
high-frequency signal to regulate the
ac line current to follow the ac line
voltage and frequency. ideally, the
ac/dc pFc stage should be equivalent
to a resistive load to eliminate the
total harmonic distortion (thD) and
maximize the power transfer.
Boost and its derivative topologies
are commonly used in the pFc stage.
this is because of their simple circuit
configurations, continuous input current, and low thD. to be compatible
with universal grid voltages (85-265 V,
47-70 hz), typically the output voltage of the boost-type pFc
stage is regulated at 390 V. there are three operation modes
for boost-type pFc converters: 1) continuous conduction
mode (ccM), 2) discontinuous conduction mode, and 3)
boundary conduction mode (BcM). For high-power onboard
charging applications, ccM is preferable because of its low
peak current and low current ratings.
Six commonly used boost-type pFc stages are shown in
Figure 6. Figure 6(a) shows the conventional single-phase

negative pulse and (b) variable frequency pulse charge (Khaligh and
Dusmez).

boost pFc converter, where a full-bridge diode rectifier is
followed by a boost converter. pFc is achieved by controlling
the duty cycle of the MoSFet to shape the inductor current
to be sinusoidal and in phase with the grid voltage. a single-phase pFc performs well for level 1 charging. however,
for level 2 charging, the inductor
becomes bulky and the components'
current stress becomes high. an interleaved boost pFc converter is preferable in level 2 chargers. Figure 6(b)
provides the schematic of a two-phase
interleaved boost pFc converter, whose
interleaving legs are operated with 180°
phase difference. the interleaved boost
pFc converter has less current stress in
each individual leg. With the ripple
cancellation effect, both the input current ripple and output capacitor root
mean square current can be reduced.
the typical experimental waveforms of
an interleaved boost pFc stage design by the power electronics energy harvesting and renewable energies Laboratory (pehreL) at the University of Maryland are
demonstrated in Figure 7. in comparison to the current ripples in each individual inductor, the current ripple in the
input side is significantly reduced.
as an alternative, the diode bridge and boost converter
can be integrated into one stage. Figure 6(c) shows a bridgeless boost pFc converter, where S1 and S2 are controlled
with the same gate signal. Figure 6(d)
is a bridgeless version of a two-phase
interleaved boost pFc converter. in
Figure 6(d), S1 and S2 are controlled
Onboard
with one gate signal and S3 and S4 are
Battery
Pack
controlled with a second gate signal.
the two channels are shifted with a
180° phase difference. Using the
bridgeless structure, the input diode
bridge can be eliminated. Fewer semiconductor devices mean less power

Bidirectional power
flow between the
grid and the vehicle
has gained interest
from academia and
industry.

Input
Filter

ac/dc
PFC
Converter

OBC
Figure 5. A block diagram of an isolated OBC.

(b)

Figure 4. The advanced fast-charging techniques: (a) CC-CV with a

Isolated Onboard PeV chargers

1Φ Grid

I E E E E l e c t r i f i c ati o n M agaz ine / december 2013

Isolated
dc/dc
Converter

Table of Contents for the Digital Edition of IEEE Electrification Magazine - December 2013