A Contactless Power Supply
`for Photovoltaic Power Generation System
`Eun-Soo Kim1, Sung-In Kang1, Kwang-Ho Yoon1, Yoon-Ho Kim2
`1Jeonju University, 1200, Hyoja-dong, Wansan-gu, Jeonju, South Korea, E-mail:eskim@jj.ac.kr
`2Chung-Ang University, 221, Heukseok-Dong, Dongjak-Gu, Seoul, South Korea, E-main:yhkim@cau.ac.kr
`
`Abstract - Among the alternative energy sources, the solar
`energy is recognized as an important energy source and its
`application is increasing. Especially in future, the hybrid solar
`energy generation system with battery and fuel cell will be widely
`used as an independent distributed power generation system. In
`this paper, a solar power hybrid home generation system using a
`contactless power supply (CPS) that can transfer an electric power
`without any mechanical contact is proposed. The proposed system
`consists of a ZVS boost converter, a half bridge LLC resonant
`converter and contact-less transformer.
`
`I.
`
`INTRODUCTION
`
`Among the alternative energy sources, the solar energy
`generation is recognized as an important energy source and its
`application is increasing. The solar generation system interfaced
`with power utility system includes DC/DC converters and
`inverters. Normally a boost type DC/DC converter is used to
`step up the input voltage. Then the inverter is used to convert dc
`to 60 Hz ac voltage to interface with power utility and this ac
`power is converted back to dc again to be interfaced with
`various home electric systems [1]. Recently, the solar hybrid
`system with battery is widely used as an independent distributed
`power generation system. If this solar energy is converted to the
`conventional utility system, then the whole energy transfer
`system is very complicate and inefficient. In future, as shown in
`Fig 1(a), it is expected that DC power service will be widely
`used for hybrid home power generation system using solar and
`fuel cell. However, such configuration of DC power service will
`cause the surge and spark voltage when the switch is turned on
`and off for connecting and disconnecting the load. To avoid
`surge voltage and risky situation, DC link voltage for DC
`power service must be limited to be used under 50VDC.
`To solve these problems, in this paper, a hybrid home power
`generation system using contactless power supply is proposed as
`shown in Fig 1(b). The proposed system consists of a ZVS
`boost converter, a half-bridge LLC resonant converter and
`contactless
`transformer.
` However, since
`the contactless
`transformer has normally large air-gap, while the leakage
`inductance increases and magnetization inductance decreases.
`This causes low power conversion efficiency.
`To overcome such problems, a series resonant converter is
`widely used [2].
`
`(a)
`
`(b)
`Fig. 1 Hybrid Photovoltaic power generation system for DC power service
`(a) The conventional DC power service using hybrid power generation system
` (b) The proposed hybrid photovoltaic power generation system
`using contactless power supply
`
`However, the series resonant converter for the contactless
`power supply generally operates with higher switching
`frequency than resonant frequency to achieve soft switching
`under continuous resonant current mode. In this case, the main
`
`978-1-4244-1874-9/08/$25.00 ©2008 IEEE
`
`1910
`
`Authorized licensed use limited to: Tamas Szepesi. Downloaded on January 20,2022 at 11:10:49 UTC from IEEE Xplore. Restrictions apply.
`
`Ex.1014
`APPLE INC. / Page 1 of 4
`
`

`

`(a)
`
`AuxLjω
`
`SCj/1 ω
`
`1lLjω
`
`2 LjN ω
`
`2l
`
`2RN
`
`eq
`
`mLjω
`
` (b)
`Fig. 2 Half-bridge LLC resonant converter using a contactless transformer (a)
`and its equivalent circuit (b)
`
`In this paper it is assumed that the winding turns-ratio
`(N=n1/n2) is equal to '1'. From Fig. 2(b), resonant frequency (fr)
`when equivalent load resistance (Req) is in short and corner
`frequency (fo) when it is open, can be obtained.
`
`f
`
`r
`
`=
`
`π2
`
`1
`⋅
`CL
`eq
`
`f
`
`o
`
`=
`
`1
`+
`
`⋅
`C)L
`m
`
`π
`2
`
`L(
`l
`
`1
`
` (2)
`
` (3)
`
`When an equivalent load resistance (Req) is in short, the
`equivalent leakage inductance (Leq) is expressed as
`
`L(L
`1
`l
`
`m
`
`L
`
`eq
`
`=
`
`+
`L
`l
`
`+
`LL)L
`2
`2
`l
`l
`+
`L
`
`m
`
`2
`
`m
`
` (4)
`
`Normalized frequency (fn = fs/fr) is a ratio between switching
`frequency (fs) and resonant frequency (fr).
`A is ratio between magnetization inductance (Lm) and primary
`side
`leakage
`inductance (Ll1).
` B
`is a ratio between
`magnetization inductance (Lm) and secondary side leakage
`inductance (Ll2). Q is a load quality factor.
`
`switches can achieve zero voltage switching (ZVS), but it has
`disadvantage that the secondary side diode converter cannot
`achieve zero current switching. Furthermore, due to the higher
`switching frequency operation than resonant frequency, it has
`low voltage gain and high power loss since a large primary side
`circulating current flows.
`Thus, in this paper, a contactless power supply using
`contactless transformer and half-bridge LLC resonant converter
`that achieves ZVS operation of main switches and ZCS
`operation of secondary side diodes is proposed. Since the
`proposed contactless power supply using LLC converter
`operates with lower switching frequency than the resonant
`frequency, it can achieve high voltage gain, which, in turn,
`offers low turns ratio for the transformer and high efficiency due
`to discontinuous resonant current.
`Based on the theoretical analysis and simulation results, the
`80W prototype is built and applied to the solar power generation
`system. The final experimental results are described.
`
`II. CHARACTERISTIC ANALYSIS OF HALF-BRIDGE LLC
`RESONANT CONVERTER
`
`The conventional series resonant inverter that is applied to the
`contactless transformer generally operates with higher switching
`frequency than the resonant frequency. However, in this paper,
`the resonant converter that operates with lower switching
`frequency than the resonant frequency is proposed for the
`contactless power supply. In this case, it has advantages that the
`problems of the conventional series resonant converter can be
`improved and high system efficiency can be obtained. Fig. 2(a)
`shows a structure of the contactless transformer that is applied
`to the half-bridge LLC converter. The primary side is a
`magnetic core but secondary side is an air-core. Large air-gap is
`made between the two sides. The large air-gap transformer has
`smaller magnetizing inductance and lower coupling coefficient
`(k) due to increase of primary and secondary side leakage
`inductances. In this type of transformers, it has some difficulty
`in transferring energy from primary side to secondary side due
`to the large magnetization current. Fig. 2(a) shows main circuits
`of a half-bridge resonant LLC converter and Fig. 2(b) shows its
`equivalent circuit. In Fig. 2(b), Vab is the terminal voltage of the
`half-bridge converter. C and Ll1 are primary side series capacitor
`and series leakage inductance respectively, Lm is magnetization
`inductance, and Ll2 and Req are secondary side leakage
`inductance and equivalent load resistance converted to the
`primary side respectively. The equivalent load resistance (Req)
`includes rectifier diode, capacitor filter and resistance.
`
` (1)
`
`R
`
`L
`
`8 π
`
`2
`
`R
`eq
`
`=
`
`f =
`n
`
`f
`f
`
`r
`
`1911
`
` (5)
`
`Authorized licensed use limited to: Tamas Szepesi. Downloaded on January 20,2022 at 11:10:49 UTC from IEEE Xplore. Restrictions apply.
`
`Ex.1014
`APPLE INC. / Page 2 of 4
`
`

`

`l1=
`Lm/LA
`
`l 2=
`Lm/LB
`
`
`Q
`
`=
`
`π2
`Lf
`eq
`r
`R
`
`eq
`
` (6)
`
` (7)
`
`constant 12VDC output using 84VDC output voltage of the
`ZVS boost converter.
`
`
` (8)
`
`
`Fig. 4 Main circuit of the contactless power supply
`for photovoltaic power generation system
`
`
`Table 1 shows the specifications and measured parameters of
`the designed system. Fig. 5(a) and Fig. 5(b) show experimental
`output waveforms with output power 80W, 7.2W respectively.
`
`
`
`
`Using equation (1) ~ (8), voltage gain (M) between input and
`output voltage can be expressed as given by
`
`
`M
`
`=
`
`1
`
`−+
`(A
`
`2
`
`)
`
`⋅
`
`A(
`
`+
`
`1
`f
`
`n
`
`1
`
`1
`
`B
`+
`B
`
`+
` (jQ)
`
`
`
`1
`
`+
`
`)(B
`
`f
`
`n
`
`−
`
` (9)
`
`1
`f
`
`n
`
`)
`
`Fig. 3 shows voltage gain characteristics with respect to fn and
`Q when the A and B are 0.384 and 0.00918, respectively. Fig. 3
`shows that the voltage gain characteristics of the proposed
`contactless power supply system are similar to that of the
`conventional LLC resonant converter. This means that the
`proposed system that operates lower switching frequency has
`similar voltage gain characteristics while it has advantages in
`achieving ZVS operation of the main switches and ZCS
`operation of the secondary side rectifier diodes. Thus the half-
`bridge LLC resonant converter applied to the contactless
`transformer has advantages in that it can achieve high efficiency
`characteristics and low output voltage noise.
`
`
`n1/n2=
`17/5=3.4
`
`22.54uH
`
`50nF
`
`51.95uH
`
`19.74uH
`
`25.6nH
`
`TABLE 1
` Specifications and measured parameters of half-bridge LLC resonant converter
`using a contactless transformer
`Transformer
`turn ratio(N)
`Equivalent leakage
`inductance(Leq)
`Resonant
`capacitor(C)
`Magnetic
` inductance(Lm)
`Primary side leakage
`inductance(Ll1)
`Secondary side leakage
`inductance(Ll2)
`
`Input
`voltage(Vin)
`Output
`voltage(Vo)
`Output
`power(Po)
`Resonant
`frequency(fr)
`Switching
`frequency(fs)
`Coupling
`coefficient (k)
`
`84VDC
`
`12VDC
`
`80W
`
`150kHz
`
`100~150kHz
`
`0.828
`
`
`
`
`
`Fig. 3 Voltage gain characteristics of half-bridge LLC resonant converter using a
`contactless transformer
`
`
`III. EXPERIMENTAL RESULTS
`
`Fig. 4 shows a main circuit of the contactless power supply
`for the photovoltaic home power generation system. The solar
`cell output voltage is boosted to constant 84VDC. The
`implemented LLC resonant converter is controlled to be
`
`(a)
`
`
`
`Authorized licensed use limited to: Tamas Szepesi. Downloaded on January 20,2022 at 11:10:49 UTC from IEEE Xplore. Restrictions apply.
`
`1912
`
`Ex.1014
`APPLE INC. / Page 3 of 4
`
`

`

`IV. CONCLUSION
`
`In this paper, a contactless power supply for a hybrid
`photovoltaic home power supply system is proposed to improve
`the efficiency of the conventional photovoltaic distributed
`power generation system. The prototype has been theoretically
`analyzed and then the 80W prototype has been built.
`The proposed system can reduce switching stress and improve
`system efficiency by ZVS and ZCS operation of switches and
`reducing energy conversion steps. The prototype has been tested
`successfully. The experimental results verified an important
`feature that the proposed system has efficiency over 80% by
`ZVS and ZCS operation, and can save complicate power
`conversion process compared to conventional utility system by
`directly supplying the dc power to the home electric system.
`
`
`
`ACKNOWLEDGMENT
`
`This work was supported by grant No. (R01-2005-000-11173-0)
`from the Basic Research Program of the Korea Science & Engineering
`Foundation
`
`
`
`REFERENCES
`
`[1] Lai, J,-S. "A High-Performance V6 Converter for Fuel Cell Power
`Conditioning System" Vehicle Power and Propulsion, 2005 IEEE
`Conference , sept 2005, pp 624-630.
`[2] Bo H. Cho, Ali Ghahary, " Design of A Transcutaneous Energy
`Transmission System Using A Series Resonant Converter", CH2873-8
`IEEE, pp. 1-8, 1990
`[3] Bo Yang, F.C Lee, A.J. Zhang, “LLC Resonant Converter for Front End
`DC/DC Conversion”, IEEE-APEC2002,Vol. 2, pp.1108-1112, 2002.
`[4] M.K Kazimierczuk, T. Nandakumar, “Class D voltage-switching inverter
`with tapped resonant inductor ” , IEEE Proceeding on Electric Power
`Applications, Vol. 140, pp.172-182, 1988.
`
`
`
`
`
`
`1913
`
`(b)
`Fig. 5 Experimental waveform of the voltage (Vab) and current (IT1) in the
`primary, and of the rectified current (IT2) in the secondary for the half-bridge
`LLC resonant converter using a contactless transformer
`(50V/div., 5A/div., 10A/div., 2us/div.) (a) 80W, (b) 7.2W
`
`
`
`
`Fig. 5 also shows that since the primary current (IT1) is
`lagging to the terminal voltage (Vab), and the secondary side
`rectifier current (IT2) is discontinuous, the main switches operate
`with ZVS and rectifier diodes operate with ZCS. Fig. 6 shows
`system efficiency characteristics with respect to output load
`variations. For the output power range of 7W~80W, the high
`efficiency characteristics over 80% was obtained. Fig. 7 shows
`the LCD TV and DVD player operating by the proposed
`contactless photovoltaic power generation system.
`
`
`86
`
`83
`
`Efficiency(%)
`
`80
`
`10
`
`20
`
`30
`
`40
`
`50
`
`60
`
`70
`
`80
`
`90
`
`Output Power(W)
`
`Fig. 6 Efficiency characteristics of contactless power supply
`
`
`Fig. 7 prototype
`
`
`
`Authorized licensed use limited to: Tamas Szepesi. Downloaded on January 20,2022 at 11:10:49 UTC from IEEE Xplore. Restrictions apply.
`
`Ex.1014
`APPLE INC. / Page 4 of 4
`
`