Solar charger with parallel resonant

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Solar Power Battery Charger with a Parallel-Load Resonant Converter

Yu-Lung Ke Senior Member, IEEE

National Penghu University of Science and Technology 300 Liu-Ho Road, Makung City Penghu County, Taiwan, R.O.C.

[email protected]

Mei-Sung Kang Department of Electrical Engineering

Kao Yuan University Kaohsiung City, Taiwan.

Ching -Ming Lai Member, IEEE

Lite-ON Technology Corp. Taiwan, R.O.C.

Abstract - Although fossil fuels have led us to economic prosperity, the extensive use has caused a substantial reduction of fossil fuels. Therefore, the solar energy, as one of the green energy resources, has become an important alternative for the future. In this paper, the parallel loaded resonant converter with the feature of the soft switching technique was used in the circuits of the solar storage battery charger. To avoid the damage of the battery charger due to the variation of the output current of the solar PV panels, a closed­loop boost converter between the solar PV panel and the battery charger was designed to stabilize the output current of the solar PV panel. By designing the characteristic impedance of the resonant tank, the charging current of the storage battery can be calculated and then the charging time for the storage battery can further be estimated. By properly designing the circuit parameters, the parallel loaded resonant converter can be operated in the continuous current conduction mode and the switch can be switched for conduction at zero voltage. The experimental results verified the correctness of the theoretic estimation for the proposed battery charger circuit. The average charging efficiency of the battery charger can be up to 88.7%.

Index Terms -- battery charger, solar power, resonant converter.

I. INTRODUCTION Energy use is one of the most important activities in human

and culture development. Among all the energy resources, the petroleum is the major one, which contributes to the quick development and prosperity of the modem society. However, the petroleum is a consumable energy. Extensive use of fossil fuels has led to the depletion of the resource. Therefore, many countries are actively searching for alternative energy resources. Currently, the alternative energy resources include solar energy, tidal energy, wind energy, geothermal energy, and biomass energy. Among these energy resources, the solar energy attracts most people's interests because it is clean and will not pollute the air. In addition, the solar energy is a natural source of energy which can be directly supplied without any effort for mining [1].

In order to store the power generated from solar cells, the storage battery is the most frequently used energy storage

Ying-Chun Chuang Member, IEEE

Kun Shan University 949 Da-Wan Road, Yung-Kang District

Tainan City, Taiwan, R.O.C. [email protected]

Yuan-Kang Wu National Penghu University of Science and Technology

300 Liu-Ho Road, Makung City Penghu County, Taiwan, R.O.C.

Chien-Chih Yu Kun Shan University

949 Da-Wan Road, Yung-Kang District Tainan City, Taiwan, R.O.C.

element. When the solar cells cannot supply power normally during the nighttime or at low illumination intensity, the storage battery can be used to supply power. The storage battery is featured with a large storage capacity and is versatile for a variety of applications. Furthermore, the storage battery has a long lifespan and its cost is lower than those of the lithium-ion battery and nickel-metal hydride battery, so it is used more frequently.

Batteries are generally used as energy storage devices to store the electric power generated by the solar energy. When at night or insufficient sunshine intensity, solar energy can not supply power electricity normally and then batteries are used to provide the power supply. Batteries themselves are provided with huge power storage capacity, widespread use, long use life and cheaper than the lithium-ion battery and nickel-hydrogen (Ni-MH) battery.

Various products and goods without environmental pollution are developed to respond energy saving and reduced carbon generation, where solar energy is one of the important resources. Because of solar energy is a natural energy resource without exploitation and environmental pollution that can be used directly. Moreover solar energy technology has gradually become mature for several years and power generation efficiency is also continuously increasing, more and more cheap pricing and easy installation. Consequently, this work adopts solar energy as the power source of battery charger. Although solar power generation is influenced by the weather and environment such that is incapable of effectively storing energy and must be effective used through converters. Hence this work designs a boost converter with closed-loop control located at the output terminal of solar energy photoelectric panels. The principal purpose is to convert the output voltage generated by solar energy after conversion of converters into a stable dc voltage applied to the charger for charging use.

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Charging technology is a technique for power supplies charging batteries and must rely on the design of the power supply [2]. The general requirement for power supplies are the adjusted output voltage variation caused by the input voltage in the specification and load change must be within a specific range. In additional to the above requirement, how to narrow the circuit volume and increase the efficiency is also the target for continuously pursuing. Traditional power supply is linear; the linear power supply (LPS) makes 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 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. Nevertheless, the SPS with advantages of small volume, light weight and low price that has lower switching losses and better efficiency than the LPS. The SPS with widespread range of input voltage is much frequently utilized than the LPS. This shows that the SPS is better than the LPS [3-4].

This study is organized as follows. Section II describes the circuit analyses and operation modes of the developed solar power battery charger with a parallel-load resonant converter. Section III shows the frequency response diagram of battery charger with parallel-load resonant converter. Section IV illustrates the design flowchart. Section V describes parameters design of the developed charger. Section VI depicts the experimental results. Conclusions are made in the Section VII. II. CIRCUIT ANALYSES AND OPERA nON 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]. When the parallel loaded resonant converter is operating in the continuous current conduction mode, it allows the switch for conduction to be operated at zero voltage so that the loss of the switching device can be reduced and thus the charging efficiency can be improved.

The DC power input side in the circuit is supplied with the DC current of the electric power converted from the optical power by the solar PV panel and then stabilized by the boost converter in the closed-loop control circuit. The DC voltage represents the stable DC voltage obtained from the boost converter in the closed-loop control circuit. In addition, the resonant tank consists of the resonant inductor and the resonant capacitor. The voltage across the input terminals is 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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current). The output voltage is then supplied to charge the storage battery.

LI .i2.. iDRt � I"

C, VORl ! iq + +

+ CI + battery Va

V, Vel

C, iD� VDRI VDll1 + +

Fig. 1. Schematic diagram of the parallel loaded resonant charger circuit The block diagram of the complete circuit of the parallel

loaded resonant charger system is shown in Fig. 2. In Figure 2, the input source of the resonant charger circuit is supplied with the DC voltage V, obtained from the boost converter in the closed-loop control circuit for power generated from the solar PV panel. After such source is supplied to the hardware circuit, it is then processed for voltage conversion by the parallel loaded resonant charger so as to obtain the required charging voltage and current for the storage battery at the output terminals.

output voltage of solar energy panel

,...------,

Fig. 2. Block diagram of the circuit of the parallel loaded resonant charger system

When the parallel loaded resonant converter is operated in the continuous current conduction mode, i.e., the switching frequency is higher than the resonant frequency, the resonant tank is operated in the continuous current conduction mode so as to allow the switch to be operated for conduction at zero voltage [7]. In this way, the instantaneous switching loss when the switch is conducting can be reduced and thus the overall charging efficiency can be improved. Based on the flow direction of the resonant current and the switching status of the switch, the continuous current conduction mode can be divided into four operation modes. The corresponding waveforms in the four operation modes are shown in Fig. 3.

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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

positive and the switch SI 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., at OJot = OJot] , the circuit enters Mode II.

Operation Mode II (OJi2 S OJot < OJot3 )

In this mode, the voltage across the resonant capacitor changes from negative to positive and the inductor current is still kept at a positive value, so the switch SI 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

current flows into D] accordingly and the circuit enters

Mode III. Operation Mode III (OJot3 S OJel < OJel5 )

V, In this mode, the input voltage becomes Va = -2 and the

inductor current changes from positive into negative till the time reaches OJel = OJri,. And then the switch S] becomes

conducting. When the voltage across the capacitor drops from a positive value to zero, i.e., at OJot = OJot5' the circuit

enters Mode IV. Operation Mode IV (OJot5 S OJel < OJel6 )

In this mode, both the voltage across the capacitor and the inductor current are negative values. When the time reaches OJel = OJri6 , the switch S] is forced to be cut off and then the

inductor current is flowing through DI.

The switching sequence of the switch for conduction is DI � SI � D] � S]. In this way, the circuit can perform a

full cycle of the operations from Figure 4 through Figure 7 and produce a complete output waveform.

+ + v, :!::

Fig. 4. Diode DI in the parallel loaded resonant charger is conducting

Fig. 5. Switch SI in the parallel loaded resonant charger is conducting

R, DR,

Fig. 6. Diode D2 in the parallel loaded resonant charger is conducting

+ v + s _

Fig. 7. Switch S2 in the parallel loaded resonant charger the diode is conducting

After the operation of the parallel loaded resonant charger circuit is clarified, the related formulation can be further derived. Based on the results of the derivation, the simulation of the circuit can be carried out and the parameters of the components can be determined. The following shows the initial conditions of the operation modes:

The Mode 1 is initiated as the diode Dl starts conducting. Figure 8 displays the equivalent circuit of the Mode 1. With this circuit diagram, the following analysis can be carried out.

Mode I (OJio S OJot < OJot] )

When the circuit is operated circuit is shown in Fig. 8.

(,(I) -

+

in Mode 1, the equivalent

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

voltage across the capacitor is vc, (OJoto) = Vco' When the

diode DI is conducting, the following equation can be

obtained.

v (t) = Vs

_ Lr diL,(t) (1) e,

2 dt

i (t) = C dVe,(t) = -L C d\,(t) (2)

c, ,. dt ,. ,. dt"

Let the parameters of the resonant frequency is defined as Eq. (3).

1 ()J =

---

o JL,C, The following equations can be obtained. d\,.(t) 1. 2

--;J;2+{)Jo IL,.(t) = -()Jo ()

d2vC,(t) 2

() _ 2 V,

--=,":"':'"+ {)Jo Vc- t - ()Jo -dr

' 2

(3)

(4)

(5)

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By using the same derivation process as in the Mode 1, the above equations can be rearranged by a collection of terms, Laplace transform, expansion of partial fractions, and then take inverse Laplace transform.

�-V i",(/)=10+(lu -1o)coS())o(t -I,)+( 2

Zo c')sin())o(t -/,)

) � � . vcr(l = 2+(VC/ -z)COS(/Jo(t -IJ + Zo(lL/ -Io)s!n((}o(t -IJ

Mode III ( {)JOt3 :<;; {)Jel < ()J(ls )

(12)

(13)

While operating In Mode III, the equivalent circuit IS shown in Fig. 10.

+ Fig. 10. Equivalent circuit when D2 is conducting

After taking the Laplace transform, the following Assume the inductor current is ir, ({)JotJ = 112 and the

equations can be obtained. voltage across the capacitor is ve, ({)JotJ = Vel' When the diode

2 Vs {)Jo -

2 V V

' 2 2 s Vc,' - S co - eo +()Jo Ve, = ---S

(6)

(7)

By expansion and the collection of the terms in partial fractions followed by the inverse Laplace transform, the following equations can be obtained.

v,,_V . 2 � . 11.,(t) =-10 +(1l0 + lo)co!fJJo(t-to)+(-z-)sIYWo(t -to) o

(8)

v" v" . vc,(t) =z + (V;,o -z)co.w,.,(t -to)+Z0(1l0 + lo)SIYWo(t -to) (9)

Mode II ( {)JOt 2 :<;; {)Jot < ()Jot3 )

While operating in Mode 2, the equivalent circuit is shown in Fig. 9.

Fig. 9. Equivalent circuit when SI is conducting Assume the inductor current iL,(OJot,) = ILl is and the voltage

across the capacitor isve,.({)J ( l2) = Vel' When the switch SI is

conducting, the following equations can be obtained.

vc,(t) = Vs

_ L,. diL,(t)

2 dt (10)

i, (t) = C dVc,(t)

= -L C d\,(t)

(,.

' dt ,.

,. dt2

(11)

D2 is conducting, the following equation can be obtained.

( ) _ V, L dil,(t)

v t ---- -- (14) e, 2 ' dt

ie,(t) = C, dVe,Ct)

= -L,.C, d\'

,

(t) (15)

dt dr

By using the same derivation process as in the Mode 1, the above equations can be rearranged by a collection of terms, Laplace transform, expansion of partial fractions, and then take inverse Laplace transform.

V, z+vc, ;",(/) = 10 + (I" -10 )COS())o (t -I,) -(----z;--)sin())o (t -I,)

Vs . Vs . Vc,(/) = --Z+(f" +-Z)COSOJo(/-/,) + Zo(lu -lo)SlnOJo(t -I,)

Mode IV ( {)JOt5 :<;; {)Jot < ()Jel6 )

(16)

(17)

While operating in Mode 4, the equivalent circuit is shown in Fig. 11.

Fig. II. Equivalent circuit when S2 is conducting

Assume the inductor current is iL,.({)Jots) = 1LJ and the

voltage across the capacitor is ve,({)Jot,) = Ve3. When the

switch S 2 is conducting, the following equation can be

obtained.

v (t) = _ Vs _ L diL,(t)

c, 2 ' dt

(18)

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i (t) = C dvc, (t) = -L C d2 iL' (t)

C, ' dt " dt2 (19)

By using the same derivation process as in the Mode 1, the above equations can be rearranged by a collection of terms, Laplace transform, expansion of partial fractions, and then take inverse Laplace transform.

¥', + ¥;3 i[,(I) = -10 + (Iu + Io)cosroo(1 - I,) - (�)sinroo(t - I,) (20) o

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 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 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

°OL-�O . 2�- O�.4--�O�.6 --����1.2�- I�.4 --�--�� 2

U = (1Js = f" "'0 fo

Fig. 12. Frequency response of the paraJIel loaded resonant charger

VI. DESIGN FLOWCHART Figure 13 shows the flow chart of the parallel loaded

resonant solar storage battery charger. The capacity of the storage battery and the range of the resonant frequencies are first determined, followed by the values of the resonant inductor and the resonant capacitor. With the IsSpice simulation, the charging current is estimated. Finally, the circuit is implemented and tested for verification. The major

objective of this paper is to design a charger with low switching loss, high efficiency and proper charging current function. For most of the conventional chargers, the switching loss is not taken into considerations so that they usually require a large heat sink. As a result, they may have the drawbacks such as bulky in size, low efficiency, cost ineffectiveness, and energy inefficiency. This paper is focused on how to avoid these drawbacks, how to reduce the switching loss during the switching operation and how to improve the overall efficiency of the charger.

No

No

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 components such as the withstand voltage and current, etc. That is, the more characteristics of the circuit are understood, the better the circuits can be designed.

Therefore, to control the level of the charging current, it is necessary to design proper parameters of the resonant tank. The resonant frequency is determined by Eq. (22).

1, = _1-o 2"�LrCr (22)

The characteristic impedance of the resonant tank IS determined by Eq. (23).

z = rz; o �C; (23)

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VI. EXPERIMENTAL RESULTS Figure 14 shows the block diagram of the closed-loop

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 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 figures show the measured waveforms of the closed-loop controlled boost converter. Figure 15 shows the saw-tooth wave and the measured waveform of the DC voltage at the 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 current waveform of the closed-loop controlled boost converter.

+ D", + VD",-

Fig. 14. Block diagram of the closed-loop controlled boost converter

Table I. Parameters for the implemented closed-loop controlled boost converter

input inductance capacitance switching duty output voltage

24Y 33�H

Tek JL

330�

o Trig'd ...

frequency

80kHz

M Pos: O.OOOs

CHI: X-axis:SIlS/div Y-axis:2V/div CH2 : X-axis:SIlS/div Y-axis:2V/div

cycle voltage

0.2 30Y

Fig. 15. Sawtooth wave and the measured waveform of the DC voltage at the proportion-integrator

Tek JL ill Trig'd ...

M Pos: 0.000,

V/JII/

i/Jm

CH I X-axis:SIlS/div Y -axis:20V Idiv CH2 X-axis:SIlS/div Y-axis: IOA/div

Fig. 16. Measured voltage and current waveforms at the diode Tek JL ill Trig'd M Pos: 0.000,

...

.. * -2*

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 Tek JL • Stop M Pos: 0.000,

...

v Cos

CH I X-axis:5Ils/div Y -axis:20V Idiv CH2 X-axis:5Ils/div Y-axis: I OA/div

Fig. 18. Measured voltage and current waveforms at the capacitor Tek JL ill Trig'd M Pos: 0.000,

2*

v" /

i /"

...

pJ

CH I X-axis:Sllsidiv Y-axis:20V/div CH2 X-axis:S\IS/div Y-axis: SA/div

Fig. 19. Output current and measured current waveform

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The measurement conditions of the parallel loaded resonant charger described in this paper are listed in Table II. The input for the device shown in the table is the output voltage obtained from the closed-loop controlled boost converter which converts the output voltage from the solar PV panel.

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Table 11. Measurement conditions of the implemented parallel loaded

Power Supply

Side

Resonant Tank

Load Side

h n I b resonant c arger or so ar storage

Input Voltage Source

30 V Resonant Resonant

Inductance Capacitance

4.1 �LH IIlF

Filter Inductance Filter

Capacitance

8.4 mH 2200 �LF

attenes Voltage

Switching Dividing Frequency Capacitance

(C, ,C,) 78 kHz lOOOIlF

Characteristic Resonant Impedance Frequency

2.1 (1 76 kHz

Load

12V, 48Ah lead-acid battery

When the design of the parameters for the charger was completed, the measurement of the implemented circuit was then carried out. The measured waveform of each component 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 voltage. Figure 22 shows the voltage across the input terminals and the current waveform at the resonant inductor in resonant tank. The voltage phase is leading the current 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 sinusoidal wave generated by the resonance in the resonant tank. Figure 25 shows the waveform of the initial output current of the parallel loaded resonant storage battery charger.

Tek JL ill Trig'd M Pos: 0.000,

2'

+

"r J

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

l

Fig. 20. Waveform at the MOSFET driving circuit

Tek

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 Fig. 21. Voltage and current wavefonns under the conduction and

cut -off conditions of the switch

Tek JL ill Trig'd +

v l( " f M Pos: 0,0005

1_-..:

CH I X-axis:2.5Ils/div Y-axis:20V Idiv CH2 X-axis:2.5Ils/div Y-axis: I OA/div

Fig. 22.Wavefonns of the voltage across the input tenninals and the current at the resonant inductor in the resonant tank

Tek JL ill Trig'd M Pos: 0.000, +

CHI: X",," : 2.5f.ls/div Y.j!dl: 20V/div CI-12 : X,fdl : 2.5f.ls/div Y",,": I OA/div

Fig. 23. Wavefonns of the capacitor voltage and the inductor current in the resonant tank

Tek M Pos: 0.000,

CH I : X .... : 2 .5Ils/div Y .... : 20V /div

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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Tek D Trig'd + M Pos: O.OOOs

1.

CH I X-axis:2.SJls/div Y -axis: IOV/div CI12 X-axis:2.SJls/div Y -axis:SAldiv

...

Fig. 25. Waveforms of the initial charging voltage and charging current at the output terminals of the charger

In this experiment, the storage battery was first discharged to 10.5V and then the charging is performed till reaching the saturation voltage of 15.8V. The data were recorded every 30 seconds in Excel. According to the variation of the voltage across the terminals of the storage battery provided in Figure 26, the voltage across the terminals of the lead-acid storage battery increases immediately to 12.5V in the beginning and 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 beginning and then charging current varies as time evolves. After the storage battery was charged to the saturation voltage of approximately 15.8V, the current of the battery reaches approximately 5.8A. The total required time for the lead-acid storage battery being discharged and then fully charged is approximately 440 minutes. The average current is 6.166A for the overall charging process. Figure 28 shows the charging efficiency of the storage battery. The lowest and highest efficiencies are around 87% and 92%, respectively, and the overall average charging efficiency is 88.7%.

vollage

16 r-------------------------�====�� 15.5 14.5

(V) 13.5 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 .,� (A) 6.0

--.� 5.5

5.0 '--____ --.,.,'--____ ---:-'--____ --:-:�----____,'------' o 100 200 300 400 time (min)

Fig. 27. Variation of the charging current of the storage battery

95.----------------------------------,

80

750�-------:-10� 0------�20 70------3�0�0------4�00�� lime (min)

Fig. 28. Variation of the charging efficiency for the storage battery

VII. CONCLUSIONS

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The parallel loaded resonant converter as a storage battery charger for solar PV panels can achieve a high charging efficiency but requires fewer circuit components. While operating in high frequency, the circuit has the advantages of compact size, lightweight and low cost. By choosing proper circuit parameters for the resonant tank, the charger can be operated under the condition of switching at zero voltage so that the loss of the switching device can be reduced and a high efficiency can be achieved.

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Maximum Photovoltaic Power Tracking Control Scheme Based on Power Equilibrium at DC Link," Industrial Electronics Society Proceedings,1999,The 25th Annual Conference of the IEEE, Vol.!, pp. 804-8090.

[2] Y. D. Chang, Implementation of Resonant Battery Charger, Master Thesis, Department of Electrical Engineering, Kun Shan University, 2004.

[3] C. M. Chou et aI, Modem Switch Power Control Circuit Design and Application, People Post and Electricity Publishing Co., People Republic China, 2005.

[4] S I Chiang, Power Electronics, Chuan Hwa Book Co , Taipei, 1998. [5] R. L. Steigerwald, "A comparison of Half-Bridge resonant converter

topologies," IEEE Trans. on Power Electronics, Vol. 3, No. 2, 1998, pp. 174-182.

[6] C. D. Cheng, Introduction to Novel Soft Switching Power Technology, Chuan Hwa Book Co., Taipei,2003.

[7] W. Hart, Introduction to Power Electronics, Prentice-Hall, Upper Saddle River, New Jersey, 1997.

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