Boost-Cascaded-by-Buck Power Factor Correction
Converter for Universal On-board Battery Charger
in Electric Transportation
A.V.J.S.Praneeth, Student Member, IEEE, Lalit Patnaik, Member, IEEE and
Sheldon S Williamson, Senior Member, IEEE
Advanced Storage Systems and Electric Transportation (ASSET) Laboratory
Smart Transportation Electrification and Energy Research (STEER) Group
UOIT-Automotive Center of Excellence (UOIT-ACE)
Department of Electrical, Computer, and Software Engineering
University of Ontario Institute of Technology,Canada
E-mail ID: Jaya.Av@uoit.net, Sheldon.Williamson@uoit.ca
Abstract—A two-stage battery charger in battery operated
electric vehicles (BEVs) and plug-in-hybrid electric vehicles
(PHEVs) with wide output voltage range of 100–500 V is most
suitable for all vehicle architectures. Existing battery chargers
have a different limited range of output voltages of 36–48 V,
72–150 V and 200–450 V is achieved by varying the output
voltage of DC/DC converters keeping a fixed voltage at DC
link. A universal charger, which can address this wide range
of battery pack voltages is suitable for all vehicle architectures.
The most feasible way to meet this requirement of wide output
voltage range is to vary the voltage at DC link with a fixed
conversion voltage ratio at DC/DC converter. In this paper, we
propose the use of cascaded converter in power factor correction
(PFC) converters to achieve the wide DC link voltages for battery
chargers. The primary focus of the paper is on the analysis and
operation of boost-cascaded by buck (BoCBB) converter. The
control implementation presented in the paper achieves a high
input power quality, wide DC link voltages with universal input
voltage ranges of 85–265 V. It also provides the degree of control
freedom to operate even if the V/Vm (output voltage to the peak
of Input) < 0.5. Simulations of the proposed converter with 1
kW power rating are carried out in PSIM 11.0 software and the
results with wide DC link voltage of 150–400 V are presented in
the paper.
Index Terms—AC–DC power converters, Power Factor
correction (PFC), Plug-in Hybrid Electric Vehicle (PHEV)/ Electric Vehicle (EV)
I. I NTRODUCTION
To reduce the carbon emissions in the environment and
encourage green energy electric vehicles (EVs) and plug-inhybrid vehicles (PHEVs) have gained a lot of interest and
attention worldwide. Battery as a source of power provides an
efficient and smooth drive compared with internal combustion
engines. Efficient on-board or off-board charging of these
battery packs is the most crucial and challenging [1]. Due
to the limitations in the fast charging infrastructure, most of
the electric vehicles are equipped with an on-board battery
charger allowing them to charge from ubiquitous utility socket
[2]. These chargers when connected to grid should adhere
harmonic regulations and standards, such as IEC 61000-
l-)))
Fig. 1: Two stage layout of on-board battery charger
3-2 and IEEE 519 for high power quality [3]. The twostage converter for EV battery charging consists of AC/DC
power factor correction (PFC) stage followed with an isolated
DC/DC converter. The most commonly used PFC converter
in all applications is with boost topology, which maintains
the high power quality for a universal input voltage of 85265 V. At high power levels, it requires a bulky inductor and
output capacitor for operation with universal input voltages
and provides efficient operation only when the required DC
output voltage is greater than peak of the input voltage
[4].Moreover,various control methods emboided using PI, PR,
nonlinear controllers in on-board battery chargers have been
studied [5]–[7].
It is an attractive solution to provide a step-up or step-down
voltage of DC output voltage for a universal input voltage
applied to the converter. However, the conventional singleswitch topologies with buck-boost configurations like conventional buck-boost, single-ended primary inductance converter
(SEPIC), flyback and Cuk converters can fulfill the operation [8]–[9] but have high component sizes and stress on
devices compared with boost PFC converters[10]–[14]. This
conventional buck-boost and Cuk converters have inverting
output voltages and provide zero direct energy transfer from
the input source to load. The minimum direct energy transfer
will increase the size of components for energy storage, which
increases the stress on the devices. The ability of direct energy
transfer path leads to lower component stress, high efficiency
of the converter and reduces the role of storage elements
for a given voltage conversion ratio [15]. The single switch
buck-boost topologies are therefore unsuitable for high voltage
applications. To mitigate the issues on stress, component
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Fig. 2: Topology of boost-cascaded by buck (BoCBB) converter
size independent controlled two-switch buck-boost converter
topologies have been proposed in literature [16]–[18]. These
converters have a non-inverting output voltage and can operate
in buck as well as boost converter based on the input voltage
applied and the desired output voltage. The challenge in these
converters is to provide a smooth transition in the change
of mode. The researchers have investigated many ways of
smooth transition implementation by providing an additional
mode between buck and boost, providing a pseudo-continuous
conduction mode state and adding a compensated duty ratio
in between the modes (pre and post buck-boost) of operations
[19]–[21]. The drawback of the topologies is complicated
control structures and less efficient due to minimum direct
energy paths. The review of topologies involved in PFC
applications are analysed with drawbacks before proposing the
control strategies[22].
This paper proposes the use of a two-switch boostcascaded-by-buck as a PFC converter is been analyzed and
the parameters are derived. The two operating modes of the
converter are explained in detail. Moreover, the design and
implementation of a control loop for the converter are also
pictured which is able to vary the PFC output voltage to a value
above and below the maximum value of the input voltage. This
variable DC-link voltage provides a smooth transition between
the buck and boost mode of operation and improves the power
quality of the converter. A 1 kW system is simulated in PSIM
and the results obtained with wide PFC voltages are presented
and discussed.
II. OPERATION OF THE PFC STAGE
In single switch buck-boost and Cuk converter topologies,
most of the power transfer from source to load happens
through the passive components which results in high voltage
and current stresses, low efficiencies. The circuit in Fig.
1 shows a two-switch boost cascaded by buck (BoCBB)
converter which consists of two switches, S1 and S2 .The total
number of switching states possible with the two switches is
four. In BoCBB converter, the converter operation is comprised
Fig. 3: Operationg modes of the BoCBB converter a) Boost mode
of operation b) Buck mode of operation
of S1 and D1 switches in boost mode of operation and the
buck mode of converter comprises of S2 and D2 . If the dc
output voltage (VDC ) is higher than the peak of the input
voltage (Vmax ), then the circuit will operate in only boost
mode and the switch S2 is turned-on continuously. If the dc
output voltage is less than the peak of the input voltage (Vmax ),
then the mode of operation of the converter will depend on the
switching states shown in Table.1 and Fig. 2. To perform the
analysis of this BoCBB converter, the following simplifying
assumptions are made:
1 All the components are ideal; ESR of the components
and forward on-state voltage drops are neglected.
2 The rectified sinewave is considered ideally same as input
sinewave, i.e.,V1 = Vm |sinωt| where Vm is the peak of
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the input voltage and ω is the angular frequency
3 The selection of the inductors (L1 and L2 ) are such that
the converter always operates in continuous conduction
mode (CCM).
4 The output capacitance of the boost converter is very
high, to which it is considered and placed across the load
to have small twice line frequency ripple and provide a
stiff output voltage Vdc .
The BoCBB converter mainly has two modes: buck mode
and the boost mode of operation. The controlling of switchS1
and diode D1 corresponds to the boost mode as shown in
Fig.3(a) and the switch S2 and D2 to buck mode as shown
in Fig.3(b).Let us define the duty ratio of the switch in
boost mode is d1 and that of in buck mode is d2 . The
BoCBB converter is a cascaded combination of two converters
(boost,buck) the overall gain (M1 ) of the converter is given in
(1)
d2
(1)
M1 =
1 − d1
which is the product of individual gains in buck and boost
mode. For analysis the forward voltage drop of the diodes is
neglected and the rectified voltage is same as the input voltage
which is given as
V1 (t) = Vm |sinωt|
(2)
where Vm is √
the maximum value of input voltage and is
given as Vm = 2Vac,rms .For a ideal PFC rectifier (neglecting
losses) the power at input and output is assumed to be constant.
For a particular value of the output voltage Vdc the input
current i1 (t) is proportional to the input voltage V1 (t)
√
⎧
⎪
⎪ i1 (t) = 2Vac,rms |sinωt|
⎨
Ri
(3)
⎪
(t)
V
⎪
⎩ i1 (t) = 1
Ri
where Ri is the emulated resistance related to active power
P demanded by the load. As shown in Fig. 4, the reference
voltage is applied to BoCBB converter with an input voltage.
For analysis one half cycle of line period with half wave
symmetry is considered. In the boost converter, the reference
voltage selected should always be higher than the peak of the
input voltage and for the buck converter, the reference voltage
should be less than the input voltage. In the interval [0, t1 ]
the converter operates in boost mode as the reference voltage
is higher than the input voltage. In [t1 , T4s ] the converter
operates in buck mode which has the input voltage is higher
than reference voltage and it repeats for [ T4s -t2 , t2 - T2s ] in
buck and boost modes. The switchover from boost to buck
mode and vice versa is taken care by the controller to provide
smooth transitions in every quarter of a cycle.
Fig. 3(a)
shows the operation of BoCBB converter in boost mode. The
boost switch cell S1 ,D1 are conducting and the buck switch S2
always on, d2 =1 and the converter is operated in continuous
conduction mode. It has the continuous load current with
low ripple current. The dc voltage gain of boost mode is
determined by the inductance volt-sec balance relation to L1 ,
Fig. 4: Waveform of the rectified input voltage and reference dc
output
L2 during on and off of the boost switch S1 over a cycle is
given as,
V1 d1 Ts + (V1 + Vc1 )(1 − d1 )Ts = 0
(4)
V1 + Vc1 (1 − d1 ) = 0
(5)
On the similar way, the volt-sec balance on ``L2 ´´gives
(V1 − Vc1 − Vdc )d1 Ts + (V1 − Vdc )(1 − d1 )Ts = 0
V1 − Vdc = Vc1 d1
(6)
(7)
The voltage gain with boost mode of operation obtained by
solving the equations (5) and (7) which is given as
1
Vdc
=
(8)
M1 =
V1
1 − d1
In the steady state operation the duty ratios are defined in
terms of the varying nature of input voltage.
⎧
⎨ d = 1 − V1 (t)
1
Vdc
(9)
⎩
d2 = 1
Fig. 3(b) shows the operation of BoCBB converter in buck
mode. The buck switch cell S2 , D2 are conducting and the
boost switch S1 always off, d1 =0 and the converter is operated
in continuous conduction mode.It also provides continuous
load current with low ripple current. The LC filter is formed
with circuit parameters L2 and C2 .The dc voltage gain of buck
mode is determined by the inductance volt-sec balance relation
L1 , L2 during on and off of the buck switch S2 over a cycle
which is given as
(V1 − Vc1 )d2 Ts + (V1 − Vc1 )(1 − d2 )Ts = 0
(10)
V1 = Vc1
(11)
(V1 − Vdc )d2 Ts + (−V1 − Vdc + Vc1 )(1 − d2 )Ts = 0 (12)
V1 d2 = Vdc
(13)
The voltage gain with boost mode of operation obtained by
solving the equations (11) and (13) which is given as
Vdc
= d2
(14)
M2 =
V1
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Fig. 5: Control loop implementation of BoCBB Converter
Fig. 6: Two loop Control implementation of converter
Fig. 8: Output voltage waveform for 400 V
Fig. 7: Input voltage and current waveforms at 400 V
In the steady state operation the duty ratios are defined in
terms of the varying nature of input voltage.
⎧
⎨ d1 = 0
(15)
V
⎩ d2 = dc
V1 (t)
The mode of operation repeats for [ T4s , T2s ]. The controller is
to be designed to provide the smooth transitions between the
modes and to have a wide DC output voltages with reduced
ripple.
Fig. 9: Input voltage and current waveforms at 250 V
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TABLE I: Parameters of the BoCBB converter
Item
Buck Mode
Boost Mode
Input Voltage Vin (rms)
Output Voltage Vdc
Power Rating
Switching frequency fs
Inductor L1
Inductor L2
Capacitor C1
CapacitorC2
Duty cycle D
Output Load Resistance R
85-265 V
250 V
1 kW
20 kHz
6 mH
2.52 mH
8 μF
950 μF
0.266
62.5Ω
85-265 V
400 V
1 kW
20 kHz
6 mH
2.52 mH
8 μF
950 μF
0.7175
160Ω
III. C ONTROL I MPLEMENTATION
Fig. 10: Output voltage waveform for 250 V reference
The layout for control implementation with the plant transfer functions is shown in Fig.6. G2 (s) is the transfer function
of current to duty ratio and G1 (s) is the transfer function
of voltage to duty ratio. The BoCBB PFC converter uses
two loop control for maintaining the wide output voltage of
converter and high input power quality. The control loop needs
to operate in boost and buck modes of operation. The detail
control structure is shown in Fig.5. Two PI control loops for
the voltage and control loops are used in boost and buck mode
to generate the duty cycle d1 andd2 . GV Bu (s) represents the
voltage controller in buck mode and GIBu (s) represents the
current controller in buck mode. Similarly,GV Bo (s) represents
the voltage controller in buck mode and GIBo (s) represents
the current controller in boost mode.
IV. R ESULTS AND D ISCUSSION
Fig. 11: Input voltage and current waveforms at 150 V
Fig. 12: Output voltage waveform for 150 V
A 1 kW BoCBB Converter model with the proposed control
has been simulated in PSIM (11.0) software with parameters
from Table I. The simulation results in Fig. 7 shows the input
voltage of 230 V(rms) applied to converter whose reference
value is greater than the peak of the input voltage. The top
waveform contains the input voltage and the reference voltage
need to be followed by the PFC converter and bottom is
the current wave which is in-phase with the input voltage
giving high power factor of 0.996. Fig. 8 shows the waveform
of output voltage of the PFC converter which is same as
reference 400 V. similarly, Fig. 9 shows the waveforms for
input voltage and current of PFC converter with the reference
voltage of 250 V. As we see the top figure contains the
reference voltage is slightly less than the peak of input voltage
making the converter to toggle between in buck and boost
modes of operation. The input current during this mode also
maintains high power quality as seen in the bottom waveform.
Fig.10 shows the waveform of output voltage of the PFC
converter which is same as reference 250 V. Fig.11, shows
the waveforms input voltage and current of PFC converter in
a buck-boost mode with a reference voltage of 150 V and Fig.
12 shows the output voltage obtained at PFC converter which
is same as a reference voltage. This fulfills the requirements of
wide output voltage control of the PFC converter maintaining
high power quality at the input side.
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V. C ONCLUSION
A non-inverting boost-cascaded-by-buck (BoCBB) PFC
converter for the universal battery charger is been simulated
to attain wide output voltages. The output voltage of PFC
converter is varied for a value greater than the peak of the
input voltage and lesser than the peak of the input voltage.
The above results show that a high power factor of 0.996 is
been achieved with the converter topology and the designed
control loops will attain universal output voltages. This wide
output voltage range at PFC converter with a DC-DC converter
can attain a wide range of battery output voltages maintaining
the high power quality at the input.
ACKNOWLEDGMENT
The authors would like to thank Natural Sciences and Engineering Research Council(NSERC), Canada Research Chairs
(CRC) Program for funding this project.
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