ISSN 2319-8885
Vol.03,Issue.11
June-2014,
Pages:2364-2369
www.semargroup.org,
www.ijsetr.com
Non-Inverting Buck–Boost Converter for Charging Lithium-Ion Battery
using Solar Array
A. SRILATHA1, M. KONDALU2, S. ANANTHASAI3
1
Assoc Prof, Joginapally BR Engineering College, Hyderabad, Andhrapradesh, India, Email: a.srilatha11@gmail.com.
Prof & HOD, Joginapally BR Engineering College, Hyderabad, Andhrapradesh, India, Email: kondalu_m@yahoo.com.
3
Asst Prof, Joginapally BR Engineering College, Hyderabad, Andhrapradesh, India, Email: ananthasai.somasi@gmail.com.
2
Abstract: As the demand for rechargeable batteries increases, so does the demand for battery chargers. There are different
kinds of design solutions available for implementing battery chargers. Generally the Buck converter topology [5] is used as a
DC- DC converter to provide the controlled output power supply to the batteries. But in this case a problem may arise, for
example, if you want to charge 5.2V Li-ion batteries from a 6V supply due to the presence of the protection diode and other
small drops across other components. This drop is generally about 1V which makes it very difficult to provide 5.2V to the Liion batteries [3] using the buck converter topology. This application note describes a simple technique for implementing a noninverting buck-boost converter [2] which requires only one inductor. This converter is basically the result of cascading a Buck
converter with a Boost converter. This converter can be controlled by two PWM signals from the PWM controller [10] and can
be used as a Buck converter or Boost converter whenever required.
Keywords: Non-Inverting Buck-Boost Converter, Lithium-Ion Battery, Constant Current And Voltage Charging.
I. INTRODUCTION
Non-inverting Buck-Boost converter can be used to charge
a wide range of the batteries using the same hardware, which
uses rechargeable batteries. The Batteries are charged in a
constant current mode till they reach full charge voltage [3].
Once the Battery reaches the full voltage, charging current
has to be reduced in order to maintain the voltage constant.
Also for Li-ion battery [3], charging has to be stopped once
the battery is fully charged. Solar array is a constant current
source; this is simple and reliable but involves a lot of
hardware. An Electronic charger can reduce the hardware in
addition to providing superior charge control characteristics.
This work describes the Design and Implementation of Noninverting Buck Boost Converter [2] which performs the task
of Efficient Battery charge regulator [1], during sun lit
conditions. This configuration can be considered as an
optimized model as it saves space, weight, cost, and which
are significantly high, in the existing method of battery
charging string switching method.
II.BATTERY CHARGING METHODS
There are several battery charging methods namely [3]
Constant current chargers vary the voltage to maintain a
constant current flow, switching off when the voltage reaches
the level of a full charge [3]. A Constant voltage charger
sources current into the battery in an attempt to force the
battery voltage up to a pre-set value (usually referred to as
the Set-point voltage or set voltage).Once this voltage is
reached, the charger will Source enough current to hold the
voltage of the battery at this constant Voltage [3] .Constant
Current-Constant Voltage charging. Used for charging
Lithium–ion batteries [3] which are vulnerable to damage if
the upper voltage limit is exceeded, Special precautions are
needed to ensure the Battery is fully charged while at the
same time avoiding overcharging. For this reason it is
recommended that the charging method switches to constant
voltage before the cell voltage reaches its upper limit. In
PWM Type the generated output voltage is less than the input
voltage. Used for most of the battery charging applications
due to single inductor topology and low complexity. [4].Buck
converter cannot be used since the input current is pulsating
so we require high input filter. In Buck Boost converter the
generated output voltage is less than or greater than the input
voltage.[5]Buck Boost converter cannot be used due to the
following limitations: The output voltage generated is
opposite in polarity to the input which is not suitable for
charging the battery as battery needs positive voltage for
charging, Polarity inverting circuitry must be employed to get
positive output, which increases the cost of the circuit.
III.PROPOSED SCHEME
Fig1. Non-Inverting Buck-Boost converter.
Copyright @ 2014 SEMAR GROUPS TECHNICAL SOCIETY. All rights reserved.
A. SRILATHA, M. KONDALU, S. ANANTHASAI
Non-inverting Buck-Boost converter as charger [1] is shown
SW1 and SW2 driven by the PWM1 and PWM2[2] signals
in Fig 1:
output by the SG1524B PWM IC[10].
IV. PRINCIPLE OF OPERATION
V. LIMITATIONS
Phase
SW1
SW2
Operating
To minimize the input current ripple at the input power
( PWM1 ) ( PWM2 )
Modes
supply, an input capacitor of high value is needed at the DCDC converter input/output current ripple is also high due to
1
ON
OFF
BUCK
output current pulsating, so a high value output capacitor is
needed. It requires additional MOSFET switch & diode, so
2
ON
ON
BUCKpower loss is high.
BOOST
3



OFF
ON
N/A
VI. NON-INVERTING BUCK-BOOST BASED
BATTERY CHARGER
In Phase 1, switch SW1 (PWM1) ON and Switch
SW2 (PWM2) is OFF and operating mode is Buck.
In Phase 2, switch SW1 (PWM1) is ON and Switch
SW2 (PWM2) is ON and operating mode is BuckBoost.
In Phase 3, switch SW1 (PWM1) is 0FF and switch
SW2 (PWM2) is ON this condition will never occur
either in a Buck converter or Boost converter.
The following guidelines are used to manage the PWM
signals shown in Fig 1.
 Keep the Frequency of both PWM signals same, to
control the synchronization of the two PWM
signals.
 The Duty cycle D1 of control signal PWM1, must
be greater than the Duty cycle D2 of control signal
PWM2.
 PWM1 signal should be enabled before the PWM2
signal.
 PWM1 signal should be disabled after the PWM2
signal.
Fig3. Battery is connected to the circuit.
VII. LITHIUM-ION BATTERY CHARGING
TERMINOLOGY
The rate of charge or discharge is expressed in relation to
battery capacity known as the “C-Rate,” this rate of charge
equates to a charge or discharge current and is defined as [3]
I = M x Cn
(1)
I charge or discharge current, M is multiple or fraction of
C, C is the numerical value of rated capacity AH, n Time in
hours at which C is declared.
Fig2. Timing diagram for two PWM signals.
From fig1: Output voltage is less than or greater than the
input voltage, Input and output voltages are of same polarity,
Single inductor Topology. Low complexity and fewer
components, there is an additional diode which prevents the
Fig 4:Li-ion Battery Charging.
output voltage going Negative, Non-Inverting Buck-Boost
converter can be used as a Buck converter or as a Boost
From fig4 batteries are charged in constant current mode
converter by selecting different combinations of switches
till they reach full charge voltage once the battery reaches
International Journal of Scientific Engineering and Technology Research
Volume.03, IssueNo.11, June-2014, Pages: 2364-2369
38
40
40
.2
40
.5
40
.8
41
34
36
vo
(vo
lts
VIII.CURRENT AND VOLTAGE MODE CONTROL
When it comes to control of the duty cycle of the switch of
a DC-DC converter, a question arises which mode of control
is to be used. There are two modes [7] Voltage mode, Current
mode.
IX.DESIGN
Input voltage: 31 V to 32.0V, Output: To charge lithiumion Battery 50 AH.[3],Charge Current: 2A,Battery Voltage:
28V to 31.8V, Battery lowest voltage is 20V,the PWM
controller is made use to design control circuit. It consists of
all circuits needed for generating PWM signal. [10], This
converter uses a switching frequency of 100KHZ [10], & the
switching element used is mosfet, the driver transformer is
1
0.5
0
)
22
26
Io(amps)
Non-Inverting Buck–Boost Converter for Charging Lithium-Ion Battery using Solar Array
full charge voltage, charging current has to be reduced in
around 100mv to 200mv.
From Fig (5)&(6) battery is
order to maintain the voltage constant, Also for lithium-ion
charged in constant current mode till it reaches a full charge
the charging has to be stopped once the battery is fully
voltage charging current has to be reduced in order to
charged. They are generally much lighter than other types of
maintain voltage constant.
Rechargeable Batteries of same size. The Electrodes of
lithium –ion Battery are made of light weight lithium and
constant current
carbon. Lithium is a highly reactive element, meaning a lot of
energy can be stored in atomic bonds. This translates in to a
very high energy density for lithium-ion Batteries. A lithium3.5
ion Battery pack looses only about 5% of its charge per
3
month. They have no memory effect, which means that you
2.5
do not have to completely discharge them before recharging.
2
Lithium-ion
batteries
can
handle
hundreds
of
1.5
charge/discharge cycles.
vo(volts)
Fig6. VIN=32.5V, EOC=31V, I=2A.
X. RESULTS&DISCUSSIONS
38
.2
38
.5
38
.9
39
36
38
vo
(v
olt
s
30
34
3.5
3
2.5
2
1.5
1
0.5
0
)
22
26
Io(amps)
constant current
vo(volts)
Fig5. VIN=32.0V, EOC=29V, I=2A.
selected such that number of primary turns equal to number
of secondary turns, Duty cycle of the series switch should
always be greater than the Shunt Switch [5], this is to ensure
Buck-Boost operation. The value of the output capacitor
controls the ripples in output voltage as well as settling time.
Higher the value of capacitor, lower the value of ripple but
higher settling time and vice versa Cmin=61.42 µF.
Capacitance of the input filter capacitor=61.42 µF. The value
of inductor chosen is 100 µ H. Current sensing resistor
(Rs)[6] is selected such that the maximum drop across it to be
Fig7. PWM IC Wave forms (simulation result).
International Journal of Scientific Engineering and Technology Research
Volume.03, IssueNo.11, June-2014, Pages: 2364-2369
A. SRILATHA, M. KONDALU, S. ANANTHASAI
Fig(7) shows the simulated waveforms of PWM IC Fig
(8)shows the charger circuit gate wave forms for both the
switches & inductor current. Fig(9)&(10)shows the hardware
results at totem pole ,gate of mosfet & pin no 7 of PWM IC.
Fig(11)shows the hard ware results of PWM IC. Fig
(12)shows the hard ware results of the charger circuit for 1A
from min to max voltage &from the wave forms we can
observe that the shunt switch is off initially & on after
32V.Fig(13)shows the series switch gate wave forms for
1A.Fig (14)shows the ripple voltage waveforms for 1A.
Fig8. Gate wave forms of both switches
current(simulation result).
& inductor
Fig9. Collector of Q1, Base of totem pole Gate of
Mosfet(hardware result).
Fig10. Gate of mosfet, Anode of diode,PIN 7of PWM
IC(hardware result).
International Journal of Scientific Engineering and Technology Research
Volume.03, IssueNo.11, June-2014, Pages: 2364-2369
Non-Inverting Buck–Boost Converter for Charging Lithium-Ion Battery using Solar Array
Fig11.Charger circuit wave forms for 1A (hardware
result).
Fig12. Series switch gate wave forms for 1A (hardware
Fig13. Ripple voltage wave forms for 1A (hardware
result).
result).
International Journal of Scientific Engineering and Technology Research
Volume.03, IssueNo.11, June-2014, Pages: 2364-2369
A. SRILATHA, M. KONDALU, S. ANANTHASAI
From the results & waveforms the power loss will occur
Engineering
Department 3301 South Dearborn Street
in the control circuit, switches, diodes, input capacitor, output
Chicago, IL 60616, USA.
capacitor, sense resistor& inductor. So the efficiency of the
system will be reduced. In order to improve the efficiency of
[6].Current
sensing
techniques
for
DC-DC
the system Operate at the optimum switching frequency to
converters,HassanpooyaForghaniZadeh,studentmember,IEEE
minimize losses. Use of improved semiconductor switches.
,and GabrielA.Rincon Mora,seniormember,IEEE Georgia
Charge at lower current rate. Disconnect charger when
Tech Analog consortium.
charging is not required. Under light-load conditions ,the
converter can operate in buck-mode with a lower switching
[7].10MHz Current Mode 4 Switch Buck BoostConverter
frequency,there by reducing
switching losses and
(4SBBC) for Polar Modulation Jinseok Park, Jiwei Fan,
consequently improving system efficiency.Use of Resonant
KevinG.Gard,AlexQ.HuangSemiconductorPowerElectronics
switching concept can also improve the efficiency.Use of
Center(SPEC)Department of Electrical and Computer
EngineeringNorth Carolina State UniversityRaleigh, North
synchronous rectification.
Carolina 27695 USAEmail: jpark3@ncsu.edu.
XI. CONCLUSION
Non-inverting Buck-Boost type Battery charger has been
[8].Design And Application GuideFor High Speed MOSFET
proposed for charging Batteries using solar array. The circuit
Gate Drive Circuits By Laszlo Balogh.
structure is simpler and much cheaper compared to other
control mechanisms where much hard ware is required. It
[9].Design Calculations for Buck-Boost Converters
operates in constant current and constant voltage (taper
Application ReportSLVA535A – August 2012 – Revised
charge) mode to efficiently and fully charge Batteries, with
September 2012.
protection features in built. The main advantage is it reduces
the hardware the disadvantage is that losses will be more in
[10].Regulating pulse width modulator SG1524B/ SG2524B/
the Buck-Boost operation Efficiency needs to be improved to
SG3524B.
make it more optimal.
XII.SCOPE FOR FUTURE WORK
The present charger is designed for a charge current of 3A.
The charge current with a higher rating can be designed.
Microcontroller based charger can also be designed with
improved closed loop control characteristics. Power
MOSFET & diodes with improved characteristics can be
used to boost the efficiency.
XIII. REFERENCES
[1]. AN2389 Application note,An MCU-based low cost noninverting buck-boost for battery chargers.
[2].Anon-invertin
buck-boost
converterwith reduced
components using a microcontroller(IEEE)ByROBERT
S.Weissbach, Member IEEE KEVIN M.TORRES,Member
IEEE.
[3].Design of high energy lithium-ion battery charger M.F.M.
Elias*, A.K. Arof**, K.M. Nor* *Department of Electrical
Engineering, Faculty of Engineering University of Malaya.
[4].Digital Combination of Buck and Boost Converters to
Control a Positive Buck-Boost Converter,Arindam
Chakraborty,Alireza Khaligh,and Ali Emadi Illinois Institute
of Technology 3301 South Dearborn Street Chicago, IL
60616, USA emadi@iit.edu .Arthur Pfaelzer Intronics, Inc.
1400 Providence Highway Norwood, MA 02062, USA.
[5].Combination of Buck and Boost Modes to Minimize
Transients in the Output of a Positive Buck-Boost Converter
Arindam Chakraborty, Alireza Khaligh, and Ali Emadi
Illinois Institute of Technology Electrical and Computer
International Journal of Scientific Engineering and Technology Research
Volume.03, IssueNo.11, June-2014, Pages: 2364-2369