1. Page 1 of 8
Solar Power Battery Charger with a Parallel-Load Resonant Converter
Yu-Lung Ke Ying-Chun Chuang
Senior Member, IEEE Member, IEEE
National Penghu University of Science and Technology Kun Shan University
300 Liu-Ho Road, Makung City 949 Da-Wan Road, Yung-Kang District
Penghu County, Taiwan, R.O.C. Tainan City, Taiwan, R.O.C.
benjamin.ke@npu.edu.tw chuang@mail.ksu.edu.tw
Mei-Sung Kang Yuan-Kang Wu
Department of Electrical Engineering National Penghu University of Science and Technology
Kao Yuan University 300 Liu-Ho Road, Makung City
Kaohsiung City, Taiwan. Penghu County, Taiwan, R.O.C.
Ching-Ming Lai Chien-Chih Yu
Member, IEEE Kun Shan University
Lite-ON Technology Corp. 949 Da-Wan Road, Yung-Kang District
Taiwan, R.O.C. Tainan City, Taiwan, R.O.C.
Abstract - Although fossil fuels have led us to economic prosperity, element. When the solar cells cannot supply power normally
the extensive use has caused a substantial reduction of fossil fuels. during the nighttime or at low illumination intensity, the
Therefore, the solar energy, as one of the green energy resources, storage battery can be used to supply power. The storage
has become an important alternative for the future. In this paper, the
battery is featured with a large storage capacity and is
parallel loaded resonant converter with the feature of the soft
versatile for a variety of applications. Furthermore, the
switching technique was used in the circuits of the solar storage
battery charger. To avoid the damage of the battery charger due to
storage battery has a long lifespan and its cost is lower than
the variation of the output current of the solar PV panels, a closed­ those of the lithium-ion battery and nickel-metal hydride
loop boost converter between the solar PV panel and the battery battery, so it is used more frequently.
charger was designed to stabilize the output current of the solar PV Batteries are generally used as energy storage devices to
panel. By designing the characteristic impedance of the resonant store the electric power generated by the solar energy. When
tank, the charging current of the storage battery can be calculated at night or insufficient sunshine intensity, solar energy can
and then the charging time for the storage battery can further be not supply power electricity normally and then batteries are
estimated. By properly designing the circuit parameters, the parallel
used to provide the power supply. Batteries themselves are
loaded resonant converter can be operated in the continuous current
provided with huge power storage capacity, widespread use,
conduction mode and the switch can be switched for conduction at
zero voltage. The experimental results verified the correctness of the
long use life and cheaper than the lithium-ion battery and
theoretic estimation for the proposed battery charger circuit. The
nickel-hydrogen (Ni-MH) battery.
average charging efficiency of the battery charger can be up to Various products and goods without environmental
88.7%. pollution are developed to respond energy saving and
Index Terms -- battery charger, solar power, resonant converter. reduced carbon generation, where solar energy is one of the
important resources. Because of solar energy is a natural
I. INTRODUCTION energy resource without exploitation and environmental
Energy use is one of the most important activities in human pollution that can be used directly. Moreover solar energy
and culture development. Among all the energy resources, the technology has gradually become mature for several years
petroleum is the major one, which contributes to the quick and power generation efficiency is also continuously
development and prosperity of the modem society. However, increasing, more and more cheap pricing and easy installation.
the petroleum is a consumable energy. Extensive use of fossil Consequently, this work adopts solar energy as the power
fuels has led to the depletion of the resource. Therefore, many source of battery charger. Although solar power generation is
countries are actively searching for alternative energy influenced by the weather and environment such that is
resources. Currently, the alternative energy resources include incapable of effectively storing energy and must be effective
solar energy, tidal energy, wind energy, geothermal energy, used through converters. Hence this work designs a boost
and biomass energy. Among these energy resources, the solar converter with closed-loop control located at the output
energy attracts most people's interests because it is clean and terminal of solar energy photoelectric panels. The principal
will not pollute the air. In addition, the solar energy is a purpose is to convert the output voltage generated by solar
natural source of energy which can be directly supplied energy after conversion of converters into a stable dc voltage
without any effort for mining [1]. applied to the charger for charging use.
In order to store the power generated from solar cells, the
storage battery is the most frequently used energy storage
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Charging technology is a technique for power supplies current). The output voltage is then supplied to charge the
charging batteries and must rely on the design of the power storage battery.
supply [2]. The general requirement for power supplies are LI
the adjusted output voltage variation caused by the input .i2..
�
I"
voltage in the specification and load change must be within a iDR t
specific range. In additional to the above requirement, how to C, VORl
narrow the circuit volume and increase the efficiency is also + ! iq
+
the target for continuously pursuing. Traditional power + battery
+ Va
supply is linear; the linear power supply (LPS) makes V, CI
Vel
progress in volume and efficiency over the switching power
supply (SPS) due to development in power semiconductor
components in the recent years. The two power supplies can C,
iD �
VDRI VDll1
be used as battery chargers, in which the traditional linear + +
power supply has relative poor conversion efficiency with
large switching losses, large weight and volume. Fig. 1. Schematic diagram of the parallel loaded resonant charger circuit
Nevertheless, the SPS with advantages of small volume, light The block diagram of the complete circuit of the parallel
weight and low price that has lower switching losses and loaded resonant charger system is shown in Fig. 2. In Figure
better efficiency than the LPS. The SPS with widespread 2, the input source of the resonant charger circuit is supplied
range of input voltage is much frequently utilized than the with the DC voltage V, obtained from the boost converter in
LPS. This shows that the SPS is better than the LPS [3-4]. the closed-loop control circuit for power generated from the
This study is organized as follows. Section II describes the solar PV panel. After such source is supplied to the hardware
circuit analyses and operation modes of the developed solar circuit, it is then processed for voltage conversion by the
power battery charger with a parallel-load resonant converter. parallel loaded resonant charger so as to obtain the required
Section III shows the frequency response diagram of battery charging voltage and current for the storage battery at the
charger with parallel-load resonant converter. Section IV
illustrates the design flowchart. Section V describes
output terminals.
output voltage of
,...----,
parameters design of the developed charger. Section VI solar energy panel
depicts the experimental results. Conclusions are made in the
Section VII.
II. CIRCUIT ANALYSES AND OPERAnON MODES
Figure 1 shows the schematic diagram of a parallel loaded
resonant storage battery charger, in which the load
characteristic at the output terminal is dependent on the ratio
of the switching frequency and the resonant frequency [5-6].
Fig. 2. Block diagram of the circuit of the parallel loaded
When the parallel loaded resonant converter is operating in resonant charger system
the continuous current conduction mode, it allows the switch When the parallel loaded resonant converter is operated
for conduction to be operated at zero voltage so that the loss in the continuous current conduction mode, i.e., the switching
of the switching device can be reduced and thus the charging frequency is higher than the resonant frequency, the resonant
efficiency can be improved. tank is operated in the continuous current conduction mode
The DC power input side in the circuit is supplied with so as to allow the switch to be operated for conduction at
the DC current of the electric power converted from the zero voltage [7]. In this way, the instantaneous switching loss
optical power by the solar PV panel and then stabilized by when the switch is conducting can be reduced and thus the
the boost converter in the closed-loop control circuit. The DC overall charging efficiency can be improved. Based on the
voltage represents the stable DC voltage obtained from the flow direction of the resonant current and the switching status
boost converter in the closed-loop control circuit. In addition, of the switch, the continuous current conduction mode can be
the resonant tank consists of the resonant inductor and the divided into four operation modes. The corresponding
resonant capacitor. The voltage across the input terminals is waveforms in the four operation modes are shown in Fig. 3.
an AC square wave at ±Vs/2 obtained by the high-frequency
switching operation of the switching device. The voltage
across the output terminals is the AC sinusoidal wave
obtained by the resonance at the resonant tank. The DC
output circuit of the charger consists of the bridge rectifier
and the LC low-pass filter, which the bridge rectifier is used
to convert the high-frequency AC current from the resonant
tank into a DC current while the LC low-pass filter is used to
remove the high-frequency noises (for both voltage and
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3. Page 3 of 8
+ +
v, :!::
Fig. 4. Diode DI in the parallel loaded resonant charger is conducting
Mode I Mode II Mode III Mode IV
Fig. 3. Waveforms at the resonant tank in the continuous
current conduction mode
Operation Mode I (OJoto S OJot < OJJ])
When the resonant current is generated atOJot = OJoto, the
inductor current iL,. is negative and the current flows through
the diode OJ. In this case, the input voltage
Vs
becomes Va = +2. AtOJri OJot1, the inductor current
= iL, is Fig. 5. Switch SI in the parallel loaded resonant charger is conducting
positive and the switch S I is conducting. In this case, the
voltage across the resonant capacitor vc, is kept at a negative
value. Once this voltage is increased to become zero, i.e.,
atOJot OJot] , the circuit enters Mode II.
=
Operation Mode II (OJi2 S OJot < OJot3 )
R, DR,
In this mode, the voltage across the resonant capacitor
changes from negative to positive and the inductor current is Fig. 6. Diode D2 in the parallel loaded resonant charger is conducting
still kept at a positive value, so the switch S I continues its
conduction state till the time when OJri = OJot3 . At that time,
+
the switch SI is forced to be cut off so that the inductor
vs +
_
current flows into D] accordingly and the circuit enters
Mode III.
Operation Mode III (OJot3 S OJel < OJel5 )
V, Fig. 7. Switch S2 in the parallel loaded resonant charger the diode is
In this mode, the input voltage becomes Va = -2 and the conducting
After the operation of the parallel loaded resonant charger
inductor current changes from positive into negative till the
circuit is clarified, the related formulation can be further
time reaches OJel OJri,. And then the switch S]becomes
=
derived. Based on the results of the derivation, the simulation
conducting. When the voltage across the capacitor drops of the circuit can be carried out and the parameters of the
from a positive value to zero, i.e., atOJot OJot5' the circuit = components can be determined. The following shows the
enters Mode IV. initial conditions of the operation modes:
Operation Mode IV (OJot5 S OJel <OJel6 ) The Mode 1 is initiated as the diode Dl starts conducting.
Figure 8 displays the equivalent circuit of the Mode 1. With
In this mode, both the voltage across the capacitor and the
this circuit diagram, the following analysis can be carried out.
inductor current are negative values. When the time reaches
OJel OJri6 , the switch S]is forced to be cut off and then the
=
Mode I (OJio S OJot < OJot])
inductor current is flowing through DI.
When the circuit is operated in Mode 1, the equivalent
circuit is shown in Fig. 8.
The switching sequence of the switch for conduction is
DI �S I � D] � S]. In this way, the circuit can perform a -
(,(I)
full cycle of the operations from Figure 4 through Figure 7
+
and produce a complete output waveform.
Fig. 8. The equivalent circuit when the diode DI is conducting
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Assume the inductor current is iL,(OJotO) = ILO and the By using the same derivation process as in the Mode 1, the
voltage across the capacitor is vc,(OJoto) = Vco' When the above equations can be rearranged by a collection of terms,
Laplace transform, expansion of partial fractions, and then
diode DI is conducting, the following equation can be
take inverse Laplace transform.
obtained. �-V ' (12)
Vs Lr diL,(t) i",(/)=10+(lu -1o)coS())o(t -I,)+( 2
c
)sin())o(t -/,)
ve,(t) = _
(1) Zo
2 dt .
vcr(l ) = 2+(VC/ -z)COS(/Jo(t -IJ + Zo(lL/ -Io)s!n((}o(t -IJ
� � (13)
dVe,(t) -L C d,(t)
ic,(t) = C =
(2)
Mode III ( {)JOt3 :<;; {)Jel < ()J(ls )
,. dt ,. ,. dt"
Let the parameters of the resonant frequency is defined as While operating In Mode III, the equivalent circuit IS
Eq. (3). shown in Fig. 10.
1 ---
()J =
LC (3)
o J, ,
The following equations can be obtained.
d,.()t 1. 2
--;J;2 +{)Jo IL,.(t) -()Jo () =
(4) +
2
d vC,(t) 2 2 V, _ Fig. 10. Equivalent circuit when D2 is conducting
--=,":"':'"+ {)Jo Vc-() - ()Jo -
' t (5)
dr 2
After taking the Laplace transform, the following Assume the inductor current is ir,({)JoJ 112 and the
t =
equations can be obtained. voltage across the capacitor is ve,({)JotJ Vel' When the diode =
(6) D2 is conducting, the following equation can be obtained.
V, dil,(t)
ve,() ---- L --
_
2 Vs t (14)
{)Jo - 2 ' dt
2 ' 2 2
Vc,' - S Vco - Veo +()Jo Ve, C, dVe,C) -L,.C,
t d'(t)
s
(7)
ie,(t)
= ---
S = = (15)
dt dr,
By expansion and the collection of the terms in partial
By using the same derivation process as in the Mode 1, the
fractions followed by the inverse Laplace transform, the
above equations can be rearranged by a collection of terms,
following equations can be obtained.
Laplace transform, expansion of partial fractions, and then
v,,_V take inverse Laplace transform.
. 2 � . V,
11.,(t) =-10+(1l0 +lo)co!fJJo(t-to)+(- -)sIYWo(t-to) (8) z+vc
,
z o ;",(/) =10 + (I" -10)COS ()) o (t -I,) -( )sin()) o (t -I,) (16)
----z;--
v" v" . .
Vc,(/) = --Z+(f" +-Z)COSOJo(/-/,)+Zo(lu -lo)SlnOJo(t -I,)
Vs . Vs
vc,(t) =z+(V;,o-z)co.w,.,(t-to)+Z0(1l0 +lo)SIYWo(t-to) (9) (17)
t
Mode IV ( {)JO5 :<;; {)Jot < ()Jel6 )
Mode II ( {)JOt 2 ()Jot3)
:<;; {)Jot <
While operating in Mode 2, the equivalent circuit is shown While operating in Mode 4, the equivalent circuit is shown
in Fig. 9. in Fig. 11.
Fig. II. Equivalent circuit when S2 is conducting
Fig. 9. Equivalent circuit when SI is conducting Assume the inductor current is iL,.({)Jos) 1LJ and the
t =
Assume the inductor current iL,(OJot,) = ILl is and the voltage
voltage across the capacitor is ve,({)Jo,) Ve3. When the
t =
across the capacitor is v e,.({)J ( l2) V el' When the switch
= SI is
switch S 2 is conducting, the following equation can be
conducting, the following equations can be obtained.
obtained.
V s L . diL,(t)
v c,(t) _ Vs diL,(t)
2
=
, dt (10)
vc,(t) = _ _ L (18)
2 ' dt
d ,(t) -L d,(t)
i,,. (t) C Vc
= , C, =
(11)
( ' dt . . dt2
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dvc, (t) d2 iL' (t) objective of this paper is to design a charger with low
iC, (t) = C = -L C (19) switching loss, high efficiency and proper charging current
' dt " dt2
By using the same derivation process as in the Mode 1, the function. For most of the conventional chargers, the
above equations can be rearranged by a collection of terms, switching loss is not taken into considerations so that they
Laplace transform, expansion of partial fractions, and then usually require a large heat sink. As a result, they may have
take inverse Laplace transform. the drawbacks such as bulky in size, low efficiency, cost
ineffectiveness, and energy inefficiency. This paper is
+
¥', ¥;3 focused on how to avoid these drawbacks, how to reduce the
i[,(I) = -10 + (Iu + Io)cosroo(1 - I,) - ( �)sinroo(t - I,)
o
(20) switching loss during the switching operation and how to
improve the overall efficiency of the charger.
III. FREQUENCY RESPONSE CURVE FOR THE
PARALLEL LOADED RESONANT CHARGER
Figure 12 shows the frequency response curve for the
parallel loaded resonant charger. According to the figure, not
all the frequencies with voltage gain occur at the spectral
positions with unity frequency gain. As a result, the voltage
gain in the parallel loaded resonant circuit is adjustable so as
to allow the user to adjust the switching frequency to
determine the output current freely. The quality factor of the
parallel loaded resonant circuit increases. It is possible to
increase the output current of the charger by changing the No
operation frequency. The output current of the charger can be
determined according to the number of batteries in series. For
a larger number of batteries in series, the charger can be
designed to operate in the range with high quality factors. In
this case, the charger functions as a boost converter. On the
contrary, for a smaller number of batteries in series, the
charger can be designed to operate in the range with low No
quality factors. In this case, the charger functions as a buck
converter. In other words, the parallel loaded resonant
converter can function either as a boost or a bulk solar
storage battery charger.
2.5
2 Fig. 13. Design process flow for the paraJIel loaded resonant charger
V. PARAMETERS DESIGN FOR THE CHARGER
In this paper, the resonant charger is operated for the
circuit with a higher switching frequency. In order to design
a high-efficiency charger, it is necessary to understand the
architecture of its circuit, the frequency variation range that
the circuit can withstand, and the specifications of its
°OL-�O .�- �--� 6 --� � �- I�--�--�� 2
�� 1.2
O .4 .�
O
2 .4 components such as the withstand voltage and current, etc.
f" = (1Js =
That is, the more characteristics of the circuit are understood,
U
fo "'0 the better the circuits can be designed.
Fig. 12. Frequency response of the paraJIel loaded resonant charger Therefore, to control the level of the charging current, it is
necessary to design proper parameters of the resonant tank.
VI. DESIGN FLOWCHART The resonant frequency is determined by Eq. (22).
Figure 13 shows the flow chart of the parallel loaded
resonant solar storage battery charger. The capacity of the 1, = _1
-
2"�LrCr
o
(22)
storage battery and the range of the resonant frequencies are The characteristic impedance of the resonant tank IS
first determined, followed by the values of the resonant determined by Eq. (23).
inductor and the resonant capacitor. With the IsSpice
simulation, the charging current is estimated. Finally, the zo = rz;
�C; (23)
circuit is implemented and tested for verification. The major
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6. Page 6 of 8
Tek JL ill Trig'd M Pos: 0.000,
VI. EXPERIMENTAL RESULTS ...
Figure 14 shows the block diagram of the closed-loop V/JII/
controlled boost converter. According to Figure 14, the
current generated by the solar PV panel must be stabilized
through a closed-loop controlled boost converter to hold
steady its voltage to avoid the variation of the voltage source i/Jm
due to the difference of the solar illumination intensity on the
solar PV panel and thus the difference of the required overall
power output. Table 1 lists the parameters used to implement
the closed-loop controlled boost converter. The following
CH I X-axis:SIlS/div Y-axis:20V Idiv
figures show the measured waveforms of the closed-loop CH2 X-axis:SIlS/div Y-axis: IOA/div
controlled boost converter. Figure 15 shows the saw-tooth Fig. 16. Measured voltage and current waveforms at the diode
wave and the measured waveform of the DC voltage at the Tek JL ill Trig'd M Pos: 0.000,
...
proportion-integrator. Figure 16 shows the voltage and
current waveforms of the diode in the closed-loop controlled
boost converter. Figure 17 shows the voltage and current
waveforms of the inductor in the closed-loop controlled boost
converter. Figure 18 shows the voltage and current
waveforms of the capacitor in the closed-loop controlled .. * -
boost converter. Figure 19 shows the output current and 2*
current waveform of the closed-loop controlled boost
converter.
CHI X-axis:5I-1-s/div Y-axis:20V/div
CH2 X-axis:5J-1s/div Y-axis: 10A/div
Fig. 17. Measured voltage and current waveforms at the inductor
+ D",
Tek JL • Stop M Pos: 0.000,
+ VD",- ...
v Cos
Fig. 14. Block diagram of the closed-loop controlled boost converter CH
I X-axis:5Ils/div Y-axis:20VIdiv
CH2X-axis:5Ils/div Y-axis: I OA/div
Table I. Parameters for the implemented closed-loop controlled boost Fig. 18. Measured voltage and current waveforms at the capacitor
converter Tek JL ill Trig'd M Pos: 0.000,
...
v
"
input switching duty output /
voltage
inductance capacitance
frequency cycle voltage pJ
24Y 33�H 330� 80kHz 0.2 30Y
i"
/
Tek JL o Trig'd M Pos: O.OOOs
...
2*
CH I X-axis:Sllsidiv Y-axis:20V/div
CH2 X-axis:SIS/div Y-axis: SA/div
Fig. 19. Output current and measured current waveform
The measurement conditions of the parallel loaded
resonant charger described in this paper are listed in Table II.
CHI: X-axis:SIlS/div Y-axis:2V/div
CH2 : X-axis:SIlS/div Y-axis:2V/div
The input for the device shown in the table is the output
Fig. 15. Sawtooth wave and the measured waveform of the DC voltage at the voltage obtained from the closed-loop controlled boost
proportion-integrator converter which converts the output voltage from the solar
PV panel.
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7. Page 7 of 8
Tek
Table 11. Measurement conditions of the implemented parallel loaded
resonant charger nor soIar storage battenes
Voltage
Power Switching Dividing
Input Voltage Source
Supply Frequency Capacitance
Side (C, ,C,)
30 V 78 kHz lOOOIlF
Resonant Resonant Characteristic Resonant
Resonant Inductance Capacitance Impedance Frequency
Tank
4.1 �LH IIlF 2.1 (1 76 kHz CH I X-axis:2.5�,s/div Y-axis:20V/div
CI-I2 X-axis:2.5�,s/div Y-axis: I OA/div
Filter
Filter Inductance
Capacitance
Load Fig. 21. Voltage and current wavefonns under the conduction and
Load Side
cut-off conditions of the switch
8.4 mH 2200 �LF 12V, 48Ah lead-acid battery
Tek JL ill Trig'd M Pos: 0,0005
+
When the design of the parameters for the charger was v
completed, the measurement of the implemented circuit was
then carried out. The measured waveform of each component
l( " f 1_-..:
is as follows. Figure 20 shows the waveform at the MOSFET
driving circuit, which provides two sets of square waves to
the active switch to perform the conduction and cut-off
operations. Figure 21 shows the voltage and current
waveforms under the conduction and cut-off conditions of
the switch, which indicates the switching operation is at zero CH I X-axis:2.5Ils/div Y-axis:20VIdiv
voltage. Figure 22 shows the voltage across the input CH2 X-axis:2.5Ils/div Y-axis: I OA/div
terminals and the current waveform at the resonant inductor Fig. 22.Wavefonns of the voltage across the input tenninals and the
in resonant tank. The voltage phase is leading the current current at the resonant inductor in the resonant tank
Tek JL ill Trig'd M Pos: 0.000,
phase, so it exhibits the property of an inductive circuit. +
Figure 23 shows the AC waveform when the capacitor
voltage resonates with the inductor current in the resonant
tank. Figure 24 shows the waveforms of voltages across the
input terminals and output terminals in the resonant tank
resonant tank. In this case, the voltage across the input
terminals is the ±Vs/2 AC square wave generated by the
switching device during high-frequency switching.
Meanwhile, the voltage across the output terminals is an AC
CHI: X",," : 2.5f.ls/div Y.j!dl: 20V/div
sinusoidal wave generated by the resonance in the resonant CI-12 :
X,fdl : 2.5f.ls/div Y",,": I OA/div
tank. Figure 25 shows the waveform of the initial output Fig. 23. Wavefonns of the capacitor voltage and the inductor current in
current of the parallel loaded resonant storage battery charger. the resonant tank
Tek JL ill Trig'd M Pos: 0.000,
+ M Pos: 0.000,
Tek
2' "r J l
CH 1 X-ax;s:2.5�s/div Y-axis: 1 OV/div
CH2 X-axis:2.5l-ls/div V-axis: I OV/div CH I : X .... : 2 . 5Ils/div Y .... : 20V/div
Fig. 20. Waveform at the MOSFET driving circuit CH2 : x .... : 2.5Ils/div Y .... : 20V/div
Fig. 24. Wavefonns of the voltages across the input tenninals and
output tenninals in the resonant tank
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8. Page 8 of 8
Tek D Trig'd M Pos: O.OOOs 95 .------,
+
1.
80
750�-------:- 0------�0 ------�0------4 00 �
10� 207 30
� � �
...
lime (min)
CH I X-axis:2.SJls/div Y -axis: IOV/div Fig. 28. Variation of the charging efficiency for the storage battery
CI12 X-axis:2.SJls/div Y -axis:SAldiv
Fig. 25. Waveforms of the initial charging voltage and charging current at the
VII. CONCLUSIONS
output terminals of the charger
The parallel loaded resonant converter as a storage battery
charger for solar PV panels can achieve a high charging
In this experiment, the storage battery was first discharged
efficiency but requires fewer circuit components. While
to 10.5V and then the charging is performed till reaching the
operating in high frequency, the circuit has the advantages of
saturation voltage of 15.8V. The data were recorded every 30
compact size, lightweight and low cost. By choosing proper
seconds in Excel. According to the variation of the voltage
circuit parameters for the resonant tank, the charger can be
across the terminals of the storage battery provided in Figure
operated under the condition of switching at zero voltage so
26, the voltage across the terminals of the lead-acid storage
that the loss of the switching device can be reduced and a
battery increases immediately to 12.5V in the beginning and
high efficiency can be achieved.
then the curve varies as the charging current changes. Figure
27 shows the charging current of the storage battery. The
charging current is very high, approximately 6.5A, in the REFERENCES
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16 r-------�====��
15.5
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12.5
11.5
10.5 L-____--:-:
':-______'--______'________-'------'
o 100 200 300 400
timc(ll1in)
Fig. 26. Variation of the charging voltage across the terminals of
the storage battery
--------------''---- --'-----------------,
7.0 ,--
--
6.5 1'+-.,..,._.....>..1.
...
charging -...�� .
current
6.0
(A)
.,�--.�
5.5
5.0 '--____--.,.,'--____---:-'--____--:-:
�----____,
'-- ----'
o 100 200 300 400
time (min)
Fig. 27. Variation of the charging current of the storage battery
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