Page 1 of 8                       Solar Power Battery Charger with a Parallel-Load Resonant Converter                     ...
Page 2 of 8   Charging technology is a technique for power supplies           current). The output voltage is then supplie...
Page 3 of 8                                                                                                               ...
Page 4 of 8        Assume the inductor current is                               iL,(OJotO)   =   ILO and the         By us...
Page 5 of 8                                 dvc, (t)              d2 iL (t)                             objective of this ...
Page 6 of 8                                                                                                   Tek         ...
Page 7 of 8                                                                                                               ...
Page 8 of 8                 Tek                 D Trigd            M Pos: O.OOOs                         95 .------,      ...
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Solar charger with parallel resonant

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Solar charger with parallel resonant

  1. 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 peoples 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 978-1-4244-9500-9/11/$26.00 © 2011 IEEE
  2. 2. Page 2 of 8 Charging technology is a technique for power supplies current). The output voltage is then supplied to charge thecharging batteries and must rely on the design of the power storage battery.supply [2]. The general requirement for power supplies are LIthe adjusted output voltage variation caused by the input .i2.. � I"voltage in the specification and load change must be within a iDR tspecific range. In additional to the above requirement, how to C, VORlnarrow the circuit volume and increase the efficiency is also + ! iq +the target for continuously pursuing. Traditional power + battery + Vasupply is linear; the linear power supply (LPS) makes V, CI Velprogress in volume and efficiency over the switching powersupply (SPS) due to development in power semiconductorcomponents in the recent years. The two power supplies can C, iD � VDRI VDll1be used as battery chargers, in which the traditional linear + +power supply has relative poor conversion efficiency withlarge switching losses, large weight and volume. Fig. 1. Schematic diagram of the parallel loaded resonant charger circuitNevertheless, the SPS with advantages of small volume, light The block diagram of the complete circuit of the parallelweight and low price that has lower switching losses and loaded resonant charger system is shown in Fig. 2. In Figurebetter efficiency than the LPS. The SPS with widespread 2, the input source of the resonant charger circuit is suppliedrange of input voltage is much frequently utilized than the with the DC voltage V, obtained from the boost converter inLPS. 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 hardwarecircuit analyses and operation modes of the developed solar circuit, it is then processed for voltage conversion by thepower battery charger with a parallel-load resonant converter. parallel loaded resonant charger so as to obtain the requiredSection III shows the frequency response diagram of battery charging voltage and current for the storage battery at thecharger with parallel-load resonant converter. Section IVillustrates the design flowchart. Section V describes output terminals. output voltage of ,...----,parameters design of the developed charger. Section VI solar energy paneldepicts the experimental results. Conclusions are made in theSection VII. II. CIRCUIT ANALYSES AND OPERAnON MODES Figure 1 shows the schematic diagram of a parallel loadedresonant storage battery charger, in which the loadcharacteristic at the output terminal is dependent on the ratioof the switching frequency and the resonant frequency [5-6]. Fig. 2. Block diagram of the circuit of the parallel loadedWhen the parallel loaded resonant converter is operating in resonant charger systemthe continuous current conduction mode, it allows the switch When the parallel loaded resonant converter is operatedfor conduction to be operated at zero voltage so that the loss in the continuous current conduction mode, i.e., the switchingof the switching device can be reduced and thus the charging frequency is higher than the resonant frequency, the resonantefficiency 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 atthe DC current of the electric power converted from the zero voltage [7]. In this way, the instantaneous switching lossoptical power by the solar PV panel and then stabilized by when the switch is conducting can be reduced and thus thethe boost converter in the closed-loop control circuit. The DC overall charging efficiency can be improved. Based on thevoltage represents the stable DC voltage obtained from the flow direction of the resonant current and the switching statusboost converter in the closed-loop control circuit. In addition, of the switch, the continuous current conduction mode can bethe resonant tank consists of the resonant inductor and the divided into four operation modes. The correspondingresonant 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-frequencyswitching operation of the switching device. The voltageacross the output terminals is the AC sinusoidal waveobtained by the resonance at the resonant tank. The DCoutput circuit of the charger consists of the bridge rectifierand the LC low-pass filter, which the bridge rectifier is usedto convert the high-frequency AC current from the resonanttank into a DC current while the LC low-pass filter is used toremove the high-frequency noises (for both voltage and 978-1-4244-9500-9/11/$26.00 © 2011 IEEE
  3. 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 978-1-4244-9500-9/11/$26.00 © 2011 IEEE
  4. 4. Page 4 of 8 Assume the inductor current is iL,(OJotO) = ILO and the By using the same derivation process as in the Mode 1, thevoltage 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 thendiode 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 ISEq. (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, thefractions 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 . Vsvc,(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 shownin 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 beconducting, 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 978-1-4244-9500-9/11/$26.00 © 2011 IEEE
  5. 5. Page 5 of 8 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 978-1-4244-9500-9/11/$26.00 © 2011 IEEE
  6. 6. Page 6 of 8 Tek JL ill Trigd 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, thecurrent generated by the solar PV panel must be stabilizedthrough a closed-loop controlled boost converter to holdsteady its voltage to avoid the variation of the voltage source i/Jmdue to the difference of the solar illumination intensity on thesolar PV panel and thus the difference of the required overallpower output. Table 1 lists the parameters used to implementthe closed-loop controlled boost converter. The following CH I X-axis:SIlS/div Y-axis:20V Idivfigures show the measured waveforms of the closed-loop CH2 X-axis:SIlS/div Y-axis: IOA/divcontrolled boost converter. Figure 15 shows the saw-tooth Fig. 16. Measured voltage and current waveforms at the diodewave and the measured waveform of the DC voltage at the Tek JL ill Trigd M Pos: 0.000, ...proportion-integrator. Figure 16 shows the voltage andcurrent waveforms of the diode in the closed-loop controlledboost converter. Figure 17 shows the voltage and currentwaveforms of the inductor in the closed-loop controlled boostconverter. Figure 18 shows the voltage and currentwaveforms 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 boostconverter. 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 CosFig. 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/divTable I. Parameters for the implemented closed-loop controlled boost Fig. 18. Measured voltage and current waveforms at the capacitor converter Tek JL ill Trigd 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 Trigd 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 outputFig. 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. 978-1-4244-9500-9/11/$26.00 © 2011 IEEE
  7. 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 Trigd 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 Trigd 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 Trigd 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 978-1-4244-9500-9/11/$26.00 © 2011 IEEE
  8. 8. Page 8 of 8 Tek D Trigd 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:SAldivFig. 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. Whileto 10.5V and then the charging is performed till reaching the operating in high frequency, the circuit has the advantages ofsaturation voltage of 15.8V. The data were recorded every 30 compact size, lightweight and low cost. By choosing properseconds in Excel. According to the variation of the voltage circuit parameters for the resonant tank, the charger can beacross the terminals of the storage battery provided in Figure operated under the condition of switching at zero voltage so26, the voltage across the terminals of the lead-acid storage that the loss of the switching device can be reduced and abattery increases immediately to 12.5V in the beginning and high efficiency can be achieved.then the curve varies as the charging current changes. Figure27 shows the charging current of the storage battery. Thecharging current is very high, approximately 6.5A, in the REFERENCES [I] M. Matsui, T. Kitano, De-hong Xu, and Zhong-qing Ying, "A Newbeginning and then charging current varies as time evolves. Maximum Photovoltaic Power Tracking Control Scheme Based on PowerAfter the storage battery was charged to the saturation Equilibrium at DC Link," Industrial Electronics Societyvoltage of approximately 15.8V, the current of the battery Proceedings,1999,The 25th Annual Conference of the IEEE, Vol.!, pp.reaches approximately 5.8A. The total required time for the 804-8090. [2] Y. D. Chang, Implementation of Resonant Battery Charger, Masterlead-acid storage battery being discharged and then fully Thesis, Department of Electrical Engineering, Kun Shan University, 2004.charged is approximately 440 minutes. The average current is [3] C. M. Chou et aI, Modem Switch Power Control Circuit Design and6.166A for the overall charging process. Figure 28 shows the Application, People Post and Electricity Publishing Co., People Republiccharging efficiency of the storage battery. The lowest and China, 2005. [4] S I Chiang, Power Electronics, Chuan Hwa Book Co , Taipei, 1998.highest efficiencies are around 87% and 92%, respectively, [5] R. L. Steigerwald, "A comparison of Half-Bridge resonant converterand the overall average charging efficiency is 88.7%. topologies," IEEE Trans. on Power Electronics, Vol. 3, No. 2, 1998, pp. 16 r-------�====�� 15.5 174-182. [6] C. D. Cheng, Introduction to Novel Soft Switching Power Technology, 14.5 vollage Chuan Hwa Book Co., Taipei,2003. (V) 13.5 [7] W. Hart, Introduction to Power Electronics, Prentice-Hall, Upper Saddle River, New Jersey, 1997. 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 978-1-4244-9500-9/11/$26.00 © 2011 IEEE

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