T. Govindaraj et al. / IJAIR
ISSN: 2278-7844
Hybrid Electric Vehicle Energy Storage System
1
1
Dr.T.Govindaraj, 2 V.Prabakaran
Head of the Department,EEE, 2 M.E.PED Scholar,
Muthayammal Engineering college,India
prabakaran.be.eee@gmail.com,
Abstract— This paper presents the modeling, design,
and novel control strategy development for a hybrid
switched-capacitor bidirectional dc/dc converter,
applicable for a hybrid electric vehicle energy
storage system. The proposed control strategy is
based on the power profile of the traction motor and
the gradient of battery current. Features of voltage
step-down, voltage step-up, and bidirectional power
are integrated into a single circuit, and are verified
on an experimental prototype. The developed
control strategy enables simpler dynamics,
compared to a standard buck converter with input
filter, good regulation capability, low EMI lower
source current ripple, ease of control, and
continuous input current waveform in both buck
and boost modes of operation.
In the boost mode, the voltage lift technique presents
an excellent method to practically implement the
proposed control strategy. Hence, by using a suitable
combination of the SCC and voltage lift technique, a
new converter with high voltage gain, high power
density, high efficiency, low EMI, ease of control and
small size can be easily constructed
This paper initially discusses the novel controller
design for 4-quadrant SC converter. Furthermore, the
paper provides a detailed insight into the operating
modes of the developed SC converter, followed by
detailed energy transfer efficiency modeling and
analyses[1]-[11]. The modeling and simulation claims
are backed up and verified by experimental test results,
in order to prove the effectiveness of the proposed
control strategy.
List of Abbreviation
II. CONTROLLER DESIGN FOR 4-Q SC CONVERTER
OPERATION
SCC
ESS
HEV
PHEV
UC
PL
POUT
Switched capacitor converter
Energy storage system
Hybrid electric vehicle
Plug-in hybrid electric vehicle
Ultracapacitor
Load power
Output power of motor
I. INTRODUCTION
A SWITCHED CAPACITOR (SC) bidirectional
dc/dc converter is a nonmagnetic converter that simply
utilizes capacitors and switches in its power stage. The
switches are controlled by capacitors, which are
charged and discharged through different paths, and
transfer their stored energy to either the high voltage
(HV) battery side, or the low voltage (LV) ultra
capacitor (UC) side. Furthermore, an SCC enables good
regulation capability, low electromagnetic interference
(EMI), lower source current ripple, ease of control, and
continuous input current waveform, in both buck and
boost modes of operation, which are critical aspects
when dealing with sensitive current applications, such
as an electric vehicle (EV) energy storage system.
A typical bidirectional SC converter consists of six
switches and two capacitors, and .Fig.1shows an SC
converter that operates in all four quadrants. Each
switch consists of two MOSFETs, for current flow in
both directions. For an HEV hybrid energy storage
system, the high voltage (HV) side typically consists of
battery modules and the low voltage (LV) side could
consist of UC modules. In this case, the high voltage dc
is set at 86 V, while the low voltage side is set at 43 V.
It must be noted here that the UC initial voltage is set at
22 V. Fig. 2 shows the complete system schematic
When the converter operates in motoring mode ,two
conditions are chosen: If the battery current gradient is
between -2 mA/sec and 2 mA/sec, battery modules
supply their energy to the load and motor side.
Otherwise, UC modules supply their power to load and
motor side. Secondly, during motoring mode, output
power of motor is compared with load power Load
power is a small rotating mechanical disk with mass500
g and length 12 mm and radius 35 mm. If , with
attention given to battery current gradient, UC or
battery modules supply their power to the motor.
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T. Govindaraj et al. / IJAIR
Otherwise, if the battery modules need energy, and fully
discharge, the UC modules transfer their energy to
battery or HV side. If the UC modules need energy, and
fully discharge, the battery modules deliver their energy
to UC or LV side. On the other hand, when the
converter operates in generating mode , only the first
condition is considered. In generating mode, the motor
tends to give up its power; thus, it is not compared with
load power. The converter and its modes of operation
are explained in the next section.
Fig. 1. Circuit schematic with hybrid energy sources and traction motor
Fig. 2. Forward motoring; capacitors and are charged by LV side (S16 is
on and current flows in motor).
III. SC CONVERTEROPERATING CHARACTERISTIC AND
MODES
In the forward motoring (Quadrant I) mode, both
voltage and current are positive. At the same time, if,
the UC or battery modules supply their power to motor
side, with attention given to the gradient of battery
current. Otherwise, battery or UC modules deliver their
energy between each other. For better understanding of
the controller, each operation mode is denoted by a
specific code.
When Pout < PL the UC modules transfer their power
to motor side. As a first step, switches S2, S10, S14 and
S7 are on D1, D9, D13 and D6 start conducting.
Capacitors C1 and C2 are charged by the LV side. At
this time, the voltage across the two capacitors
ISSN: 2278-7844
increases. Also, in this operation mode, S16 is on,
because motor does not stop, and current flows through
the armature. This mode is represented by code 3. The
operation mode is shown in Fig.3.
After this operating stage S6, S11and S4 are on, and D7
D12 and D3 start conducting. Capacitors C1 and C2 are
disconnected from LV side and transfer their stored
energy to motor side. At this time, the voltage across
the two capacitors de creases. This mode is shown by
code 1. This operation mode is depicted in fig 4.
However, when battery modules deliver their energy to
motor side, switch S5 is closed, and D8 starts
Conducting. This mode is shown by code 2, and is
Depicted in Fig.4.
Now, if, and battery modules are fully discharged LV
side or UC modules transfer their energy to HV side.
As a first step, switchesS2, S10, S14, and S7 are on, and
D1, D9, D13 and D6 start conducting. This mode is
Represented by code 3 and is depicted in Fig.2. Also, in
both buck as well as boost modes switch is on, because
motor does not stop, and current flows through the
armature. After this operating stage, S6, S11, S4, and
S8 are onD7, D12, D3and D5 starts conducting.
Capacitor and are disconnected from LV side and
transfer their stored energy to the HV side. Also, the
voltage across two capacitors decreases. This mode is
shown by code 4.
The boost mode implements the voltage-lift technique
Because the capacitor s are charged in parallel During
the on-state the input voltage appears Across the
capacitors. The capacitors are discharged in series
during the Off-state. Hence, through this simple
technique, output voltage can be boosted by the
capacitors. This operation mode is depicted in Fig. 5.
Now, if, and UC modules are fully discharged battery
modules transfer their energy to the LV side. As a first
Switches S5, S3, S12, and S7 are on, and D8, D4,
D11andD6 start conducting. Now, capacitors C1 and
C2 are charged by HV side. At this time the voltage
across the two capacitor increases. This mode is
Representation by code 10 and is shown in fig.6
After this operating stage switches S6, S9, S13,
and S1 are on and D7, D10, D14, and D2 start
conducting. Capacitor C1 and C2 are Disconnected
from HV side and transfer their Stored energy to the
LV side. At this time the Voltage across the two
capacitor decreases. This Mode is shown by code
11.the buck mode uses the current amplication
technique, because the Capacitors are charged
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T. Govindaraj et al. / IJAIR
ISSN: 2278-7844
Fig.3. Forward motoring; capacitors are discharged and are disconnected
from LV side
Fig. 7. Capacitors are discharged and are disconnected from HV side ( is
on and current flows in motor).
Fig. 4. Forward motoring; battery modules supply energy to motor.
Fig. 8. Forward motoring; hybrid energy sources are fully discharged (
and is on).
Fig. 5. Capacitors are discharged and are disconnected from LV side ( is
on and current flows in motor).
Fig. 9. Forward regenerative operation; capacitors and are charged by
Motor
Fig. 6. Capacitors and are charged by HV side (is on and current
Flows in motor).
in series during on state. The input current flows
through capacitors these Capacitors are discharged in
parallel during off-state. The output current is amplified
by these capacitors this operation mode is depicted in
Fig. 7.
If UC or battery modules are fully discharged, and
turns on, because current flows through the motor. This
mode is represented by code 9. This operation mode is
shown in Fig. 8.
In forward regenerative (Quadrant II) mode, voltage is
positive and current is negative. In this operating mode,
only battery current gradient is considered. When
Motor supplies power to the UC side, and UC modules
are fully discharged (or half charged), then the mo tor
transfers its power to the LV side. As a first step,
switches S3, S12, and S7 are on, and D4, D11, and D6
start conducting. Capacitors and are charged by motor
Power. At this time, the voltage across the two
capacitors increases. This mode is represented by code
zero, and is shown in Fig.9.
After this operating stage, switches S6, S9, S13, and
S1 are on, and D7, D10, D14 start conducting.
Capacitors C1 and C2 stored are disconnected from
motor side and transfer their energy to the LV side. At
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T. Govindaraj et al. / IJAIR
this time, the voltage across the two capacitors
decreases. At the same time, switch is on, because
motor does not stop. This mode is shown by code 12,
ISSN: 2278-7844
However, if UC or battery modules are fully charged
Switch is on, because current flows through the motor.
This mode is shown by code 8, and is depicted in
Fig. 12.
In reverse motoring (Quadrant III) mode, both voltage
And current are negative. This operation mode and
Its codes are same as forward motoring mode. In
reverse regenerative (Quadrant IV) mode, voltage is
Negative and current is positive. This operation mode.
And its codes are same as forward regenerative mode.
The next section focuses on critical energy transfer
Efficiency modeling and analysis of the SC converter.
and is depicted in Fig.10.
Fig. 10. Forward regenerative operation; capacitors and are disconnected from motor side and transfer their stored energy to the LV side
(is on and current flows in motor).
Fig. 11. Forward regenerative operation; battery modules are fully
discharged or half charged
IV.ENERGY TRANSFER EFFICIENCY MODEL
AND DESIGN
As aforementioned, the SC converter has two main
modes of operation, the buck mode and boost mode.
The buck modes use the current-amplification
technique Capacitors and are charged during on-state in
series and input current flows through them. These
capacitors are discharged during off-state in parallel.
Therefore, the output current is amplified by these
capacitors. If the switching period T, is small enough
(compared to the circuit time constant), an average
current can be used to replace its instantaneous value,
for the purpose of integration. Also, it must be noted
that capacitors and are of equal sizes, so that the voltage
across each of them is equal. Therefore, the voltage
across capacitor can be expressed as shown in (1) at the
bottom of the page. If the switching period, is small
enough (compared to the circuit time constant), initial
values can be used, while ignoring trivial variations.
Therefore, the current flowing through capacitor can be
written.
Fig. 12. Forward regenerative operation; UC or battery modules are
fully charged and current flows in motor
When the motor supplies power to battery side, and
battery modules are fully discharged (or half charged)
motor transfers its power to HV side, and switch turns
On. Diode starts conducting, and this mode is
represented by code 5, as showninFig.11.
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T. Govindaraj et al. / IJAIR
ISSN: 2278-7844
the scenario when battery modules supply their energy
to motor side (code2). Consider codes 3 and 1, Pout<PL
and UC modules transfer their power to motor side. Fig.
16 depicts the voltage across of each capacitor, voltage
across the dc motor (armature voltage), and operation
(gate-to-source voltage) of switches and during codes 3
and 1, respectively. under code 3 operation, when
switch is on, capacitors and are charged by LV side in
parallel, and voltage across, of each capacitor increases.
Also during this interval, is on because motor does not
stop. After this operating stage, during operation in
code 1, when switch is on, capacitors and are
disconnected from LV side,C1 and C2 transfer their
stored energy to motor side. At this time, the voltage
across each capacitor decreases.
TABLE-1
Fig. 15 shows UC module voltage that gradually
decreases and supplies power to motor. Fig. 14
represents UC module current and gate-to-source
voltage of S2.depicts motor voltage, current, and
operation of switch S4.Operation of switches S2, S10,
S7, S11, S4 and S16 are shown in Fig. 21. As is clear,
when the converter is operated under code 3. S2, S10,
S14, S7 and S16 are on, and D1, D9, D13and D6 start
conducting (capacitors C1 and C2 are charged by the
LV side). Under code 1 Operation, S6, S11and S4 are
on, and D7, D12 and D3 and start conducting.
Capacitors C1 and C2 are discharged and transfer their
stored energy to motor Side.
Fig. 17 shows the overall computed energy transfer
Efficiency versus varying conduction duty cycle, k
Fig. 13. Experimental setup for implementing the SC converter
V. EXPERIMENTAL SETUP AND TEST VALIDATION
This section focuses on the experimental
implementation and controller verification for the
proposed 4Q SC converter. Fig.13. Shows the
experimental setup, which is used for practical
implementation of the SC converter. The experimental
test setup consists of 24 cells Li-ion polymer battery
cells (10 Ah, 16 cells, BCAP 120 0 P270) and a 1 HP
permanent-magnet dc machine (PMDC).
A micro controller is used to implement the control
strategy. Micro controller is a digital controller for
rapid prototyping .which can be directly programmed
with the Simulink file used
Average transfer efficiency in this mode is calculated
to be about 87%. Thus, it is evident that conduction
duty does not affect the transfer efficiency significantly.
However, does affect Pi (input power) and Pout (output
power) in a diminutive region.
Considering code 2, when battery modules are fully
Or half charged, UC modules are fully discharged and
Pout<PL.When the motor demands power, battery
modules Supply their power to the motor, and LV side
is fully Discharged. In this case, battery modules,
instead of the LV side (UC modules), supply their
energy their energy to the motor in both operating
modes (forward motoring and reverse motoring). Fig.
14 show motor as well as battery voltage and current,
B. Experimental Test Results and Discussion
This section focuses on the experimental test results of
codes3 and 1. Additional test results include testing of
© 2012 IJAIR. ALL RIGHTS RESERVED
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T. Govindaraj et al. / IJAIR
ISSN: 2278-7844
Fig:16
while depicts operation of switch .Table II shows the
efficiency comparison between the conventional 4-Q SC
converter and proposed 4-Q SC converter.
Fig:17
Fig:14
VI-Conclusion
Fig:15
This paper presented the design and experimental
verification of a novel control technique for a hybrid SC
bidirectional dc/dc
converter,
applicable
for
HEV/PHEV energy storage system application. The
developed SCC offers essential features of voltage stepdown, voltage step-up, an d bidirectional power flow,
associated with two or more HEV energy storage
devices Furthermore, this paper also presented detailed
efficiency modeling and analyses using the proposed
SCC control strategy. Experimental tests conducted on
the proposed topology depict the following major
advantages: a) lower source current ripple b) simpler
dynamics; and c) control simplicity. The verification
tests were satisfactory from the point of view of
Modeling simulation, and experimental verification.
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509
T. Govindaraj et al. / IJAIR
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ISSN: 2278-7844
system Engineering and Intelligent controllers.He is a Fellow of
Institution of Engineers India(FIE) and Chartered Engineer
(India).Senior Member of International Association of Computer
Science and Information. Technology (IACSIT). Member of
International Association of Engineers(IAENG), Life Member of Indian
Society for Technical Education(MISTE). Ph.D. Recognized Research
Supervisor for Anna University,Satyabama University Chennai and CMJ
University Meghalaya. Editorial Board Member for journals like
International
Journal
of
Computer
and
Electrical
Engineering,International
Journal
of
Engineering
and
Technology,International Journal of Engineering and Advanced
Technology (IJEAT).International Journal Peer Reviewer for Taylor &
Francis International Journal “Electrical Power Components & System”
United Kingdom,Journal of Electrical and Electronics Engineering
Research,Journal of Engineering and Technology Research
(JETR),International Journal of the Physical Sciences,Association for
the Advancement of Modelling and Simulation Techniques in
Enterprises,International Journal of Engineering & Computer Science
(IJECS),Scientific Research and Essays,Journal of Engineering and
Computer Innovation,E3 Journal of Energy Oil and Gas Research,World
Academy of Science, Engineering and Technology,Journal of Electrical
and
Control
Engineering（JECE),Applied
Computational
Electromagnetics Society etc.. He has published Seventy Six research
papers in International/National Conferences and Journals. Organized 20
National / International Conferences/Seminars. Received Best paper
award for ICEESPEEE 09 conference paper. Coordinator for AICTE
Sponsored SDP on Soft Computing Techniques In Advanced Special
Electric Drives,2011.Coordinator for AICTE Sponsored National
Seminar on Computational Intelligence Techniques in Green Energy,
2011.Chief Coordinator and Investigator for AICTE sponsored
MODROBS - Modernization of Electrical Machines Laboratory.
.
[7] F. L. Luo and H. Ye, Advanced DC/DC Converters. Boca Raton,
FL: CRC, 2004.
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converter,” in Proc. IEEE Annu. Conf. Ind. Electron. Society, Paris,
France, Nov. 2006, pp. 2073–2076.
[9] M. Veerachary and S. B. Sudhakar, “Peak-current mode control of
hybridswitched capacitor converter,” in Proc. IEEE Int. Conf. Power
Electron., Drives, Energy Syst., New Delhi, India, Dec. 2006, pp. 1–
6.
[10] F. L. Luo, “Luo converters, voltage lift technique,” in Proc. IEEE
Power Electron. Specialists Conf., Fukuoka, J Japan, May 1998, pp.
[11] Govindaraj Thangavel,” Finite Element Analysis of the Direct
Drive PMLOM” In book: Finite Element Analysis - New Trends and
Developments, Chapter: 6, InTech online Publisher,10 Oct 2012.
Dr.Govindaraj Thangavel born in Tiruppur , India
, in 1964. He received the B.E. degree from
Coimbatore Institute of Technology, M.E. degree
from PSG College of Technology and Ph.D.
from Jadavpur University, Kolkatta,India in 1987,
1993 and 2010 respectively. His Biography is
included in Who's Who in Science and
Engineering 2011-2012 (11th Edition). Scientific
Award of Excellence 2011 from American
Biographical Institute (ABI). Outstanding Scientist of the
21st century by International Biographical centre of
Cambridge, England 2011.
Since July 2009 he has been Professor and Head of the Department of
Electrical and Electronics Engineering, Muthayammal Engineering
College affiliated to Anna University, Chennai, India. His Current
research interests includes Permanent magnet machines, Axial flux
Linear oscillating Motor, Advanced Embedded power electronics
controllers,finite element analysis of special electrical machines,Power
.
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