Experimental Verification and Analysis of AC-DC Converter with an nput mpedance Matchg for Wireless Power Transfer Systems Keisuke Kusaka, Jun-ichi toh Nagaoka University of Technology 63- Kamitomioka-machi Nagaoka Niigata, JAPAN Tel.: 8 / (58) 47 9563. Fax: 8 / (58) 47 9563. E-Mail: kusaka@stn.nagaokaut.ac.jp, itoh@vos.nagaokaut.ac.jp URL: http://itohserver.nagaokaut.ac.jp/itohlab/en/dex.html This work was supported by Japan Society for the Promotion of Science; Grant--Aid for Scientific Research (B), 4366. Keywords «Wireless power transmission», «Power converters for EV», «High frequency power converter» Abstract This paper discusses the performance of an AC-DC converter which converts power from 3.56- MHz AC to DC a receivg side of wireless power transfer systems. The wireless power transfer systems are required to operate high-frequency such as 3.56 MHz order to achieve a high power density of transmission coils. Thus the AC-DC converter the receivg side is demanded to operate at high-frequency. n such high-frequency region, the reflected power occurs when the put impedance is not matched to the characteristic impedance of the transmission le. n other words, the put impedance of the AC-DC converter needs to have the same impedance to the characteristic impedance of the transmission le. n order to overcome the problem, the AC-DC converter with an put impedance matchg is proposed this paper. The proposed AD-DC converter achieves the put impedance matchg with a simple circuit configuration. t means that the converter can obta susoidal put current and unity put power factor without a high-frequency switchg except the diodes. n this paper, the impedance matchg characteristics and the analysis of the operational modes of the proposed circuit are presented. The experimental results confirmed that the proposed converter enables a conversion from 3.56-MHz AC to DC with the susoidal put current. n this operation condition, the put impedance is 9.6 j.5. Because the design value of the put impedance is 5 j, there is a non-negligible error on the real part. This is attributed to the parasitic capacitances on the diodes. n order to solve this problem, an improved AC-DC converter is proposed newly. From experimental results, it achieves the put impedance of 5.7 j. Besides, the reflection coefficient is suppressed by up to 94.5% compared with that of the conventional capacitor put-type diode bridge rectifier (C-DBR).. ntroduction n recent years, wireless power transfer methods have been attracted the community [-]. n particular, the wireless power transfer with magnetic resonance couplg (MRC) which is reported by A. Karalis et al. 7 is heavily studied [3-4]. The MRC shows better features compared with the conventional wireless power transfer methods such as an electromagnetic duction and a microwave transmission. First, the MRC allows a wireless power transfer a middle-range transmission distance such as a few dozen of centimeters at high efficiency of over 9% [5]. Such high transmission efficiency cannot be achieved with an electromagnetic duction. On the other hand, the transmission efficiency of a microwave transmission is greater than the others. However, the conversion efficiency between microwaves from electrical power is mere 84.4% [6].
Second, the declation of the transmission efficiency caused by a position gap of the transmittg devices is relatively small. These advantages are featured by the characteristic constructions of the transmittg coils. The transmission efficiency at a resonance frequency is expressed by (). t represents the transmission efficiency is determed by an only product of the quality factor of the transmittg coil Q and the couplg coefficient k. The transmittg coils have a high quality factor Q owg to the low parasitic resistance of the coils. The high quality factor allows an efficient wireless power transfer a middle-range transmission distance even when the couplg coefficient is small [7-8]. () kq Considerg to apply the wireless power transfer with MRC to the battery chargers for electrical vehicles (EVs), the coils for the transmittg side and receivg side are planted on the ground parkg areas, and underneath of EVs, respectively. This technology brgs convenience to users because users are not required to charge the battery with electrical cables [9]. n the wireless power transfer system with the MRC, the size of the transmittg coils depends on the transmittg frequency []. Thus, the wireless power transfer systems are expected to operate high-frequency order to achieve a high power density. Moreover, MRC should be operated dustrial scientific medical (SM) band such as 3.56 MHz and 7. MHz because noise from the wireless power transfer systems is prohibited to fluence the operation of neither the electronic devices nor the radio communication equipment. On the receivg side of wireless power transfer systems, the AC-DC converter, which converts the power from 3.56 MHz to DC, is necessary. The previous studies have reported that the use of the diode bridge rectifier on the receivg side []. The diode bridge rectifier has a distorted put current and low put power factor. Furthermore a diode bridge rectifier is connected to a DC load, the put impedance of the diode bridge rectifier depends on a load on a DC side. n such high-frequency region, an impedance matchg is very important order to suppress the reflected power []. Eventually, the reflected power which is generated by the put impedance mismatchg decreases the transmission efficiency []. Besides, the characteristic impedance of the transmission le such as a coaxial cable is set to 5 j. Although, the matchg function is required the AC-DC converter, a method of an put impedance matchg for the AC-DC converters has not been reported. This paper proposes and demonstrates an put impedance of the AC-DC converter which can be matched to the characteristic impedance of 5 j. First, the configuration of the proposed AC-DC converter is described. The AC-DC converter achieves the put impedance matchg without highfrequency switchg devices except the diodes. Then, the operation modes of the proposed converter are analyzed. n particular, the formulas for the put current are derived. Fally, the AC-DC converter is tested experimentally.. Proposed AC-DC Converter with nput mpedance Matchg.. Requirements for nput mpedance Matchg Generally, high-frequency circuits are constructed with an impedance matchg order to suppress reflected power []. The impedance matchg can be described as; the output impedance of the power supply and the put impedance have equal impedances to the characteristic impedance of the transmission le. n particular, the characteristic impedance of a 5 is used widely. For this reason, 5 is used as the characteristic impedance and also the put impedance of the AC-DC converter this paper. Besides, the put impedance of AC-DC converters with a battery as a load is required to match an put impedance regardless of the load conditions. n general, the characteristic impedance of transmission les, which is the reference value of the put impedance of the AC-DC converter, does not clude an imagary part. Thus, an put voltage and current of the AC-DC converter are required to fulfill the followg requirements, where Ż is the put impedance, V is the fundamental put voltage of the AC-DC converter, İ is the fundamental put current and is the phase angle between the put voltage and the put current. (a) Z V 5
(b) nput power factor is (cos = ) n a low-frequency region, power factor correction (PFC) circuits with a PWM control are used widely [3]. The PFC circuits with a PWM can satisfy the above-mentioned conditions easily due to the put current control with the PWM a low-frequency region. However, the switchg frequency for the PWM requires higher frequency than an put frequency. Thus, it is difficult to operate the conventional PFC circuits when the put frequency is constraed a high-frequency such as 3.56 MHz. n conclusion, an AC-DC converter with a simple circuit configuration which can achieve the put impedance matchg is required on the receivg side of the wireless power transfer system... Circuit configuration Fig. presents the circuit configuration of the proposed AC-DC converter. The proposed converter consists of the resonant-type rectifier which is reported by K. Matsui et al. [4] and the bidirectional boost chopper. The resonant-type rectifier achieves a PFC operation usg a resonance between the ductor which is connected series to the put termal and the capacitors parallel to the upper arm. The resonant-type rectifier has been demonstrated a commercial frequency [4]. However, this converter causes a low power density the low-frequency operation because a bulky ductor and capacitors as resonance components are required. Additionally, the possibility of the put impedance matchg is not discussed. n this paper, the resonant-type rectifier is operated at high-frequency. Furthermore the function of the put impedance matchg is evaluated. The high-frequency operation improves the power density owg to the downsizg of the passive components. n addition, Ref. [4] poted out that the amplitude of the put current and the put power factor hge upon a load condition when a resistance load is connected directly to the resonant-type rectifier. t means that the put impedance of the stand-alone resonant-type rectifier depends on the load conditions. n order to overcome this problem, the bidirectional boost chopper is connected at the output side of the resonant-type rectifier Fig.. The bidirectional boost chopper is operated purpose to fix the operatg pot which is decided by the rectifier output voltage of the resonanttype rectifier. The MOSFET S is used for an itial charge of the C 4 stead of a diode because the put power factor closes to zero when the rectifier outputs voltage is around zero. The control for the chopper circuit does not need a high dynamic response. Thus, the chopper circuit does not need either a high-speed or a high-frequency switchg. Thus, the chopper may be operated at a low switchg frequency such as khz. However, a switchg frequency of khz is selected this paper with the objective of the downsizg of the ductor L. f sw = khz S Resonant-type rectifier i ch Ż v i 3.56 MHz D D C C L C 3 C 4 i c L S C 5 v conv V B D 3 D 4 Fig.. The proposed AC-DC converter..3. Control method of bidirectional boost chopper Fig. shows the control block diagram of the bidirectional boost chopper. The voltage control is composed by an automatic voltage regulator (AVR) with a P control and an automatic current regulator (ACR) as an ner loop of the AVR, where the natural angular frequencies of the AVR and ACR are 4 rad/s and 4 rad/s respectively. Note that T ic and T iv are the tegral time of the ACR and AVR, respectively. The put impedance is determed by the relation among the voltage ratio V, the ductance L and the capacitances C and C where the voltage ratio is the ratio of the rectifier output voltage to the put maximum voltage V m. The voltage ratio should be stabilized constant
order to obta the tended put impedance when the put power is constant. Thus, the voltage ratio is controlled through the rectifier output voltage control, where the reference value of the rectifier output voltage is obtaed by (). * * vch V m V () n the proposed circuit, a fast dynamic response of the bidirectional boost chopper is not necessary because the put maximum voltage is not changed fast. For this reason, an expensive generalpurpose controller can be used. Note that, the capacitance C 3 is negligible the AVR because the capacitance C 3 is enough smaller than C 4 the control block diagram. V * * st iv P i ch * st ic P v conv sl i ch sc 4 V m Fig.. The control block diagram for the proposed AC-DC converter.. Operation modes of the proposed AC-DC converter Fig. 3 shows the operation modes of the proposed converter. Note that the bidirectional boost chopper with AVR is illustrated as an ideal DC voltage source. Fig. 4 illustrates the simplified operation waveforms when the proposed converter is operated at the unity put power factor. n this chapter, the forward voltage drop of the diodes is ignored for simplicity. The circuit operations each four operation are described the followg statements. 3.. Operation mode nput current i flows through the ductor L, capacitors C and C. The capacitors C and C are discharged and charged respectively by the put current. The put current a mode i _ is derived from a circuit equation as CVm Cv ch i t t t t _ cos cos s (3), where C=C =C, L is the ductance of the ductor L, V m is the maximum put voltage, is the put angular frequency and is the resonance angular frequency which is expressed as (4). Note that the resonance angular frequency is obtaed as a series resonance of the ductance L and the two capacitances C. (4) LC V v D C i i L du i cu v D C vcv i dv i cv i v D i L du C D C i cu i dv i cv vcv i Mode Mode v cv D C i i L du i cu v D C v cv i dv i cv i v D i L du C D i cu i dv C vcv i cv i du i cu i dv i cv Mode Mode V Fig. 3. Operation modes of the proposed circuit. T T Fig. 4. Simplified waveforms of the proposed AC-DC converter.
From (3), the put current cludes both the frequency components; resonance angular frequency and put angular frequency. Thereby, the put current is not a complete susoidal waveform. The capacitor C, which had charged operation mode, is discharged by the put current. n contrast, the capacitor C is charged gradually. After the capacitor voltage v cv reaches to the DC voltage, the next operation mode will start. ncidentally, the period of the operation mode T is equal to the dischargg time of the capacitor C. Thus, this period T can be derived from (5) with the numerical analytical approach. vch V m cos s s T T T (5) 3.. Operation mode The put current commutates to the diodes D from the capacitor C because the diodes D and D 4 become a turn-on. The put current flows to the path that is formed by ductor L, diodes D and D 4. n this mode, the smoothg capacitor is charged by the put current, which is expressed by vch i_ t i_ cos t T t T tt s L V cos T V cos t T cos t T m (6), L s T t T t T m s s L where i _ (T ) is the itial value of the put current which is also expressed as i _ (T ), is the resonance angular frequency which is expressed by (7). Also, the put current the mode is not a complete susoidal. (7). LC 3 Besides, (6) can be simplified as (8), when the resonance angular frequency is enough small to be ignored. Generally, the capacitance C 4 has a large capacitance because it should compensate the voltage fluctuation which is caused by the bidirectional boost chopper. vch Vm i_ t i_ t T t T cost cost (8) L L Besides, the capacitor voltages and v cv are not changed this mode. The mode contues until the put voltage polarity is changed from positive to negative. 3.3. Operation mode n this mode, the put current flows the opposite direction to the mode via C, C and L. n this mode, the put current is expressed by i _ (t) = -i _ (t-t/) where T is the put period. The capacitors C and C are discharged and charged respectively by the put current. The mode contues until the capacitor voltage reaches to the DC voltage. The period of the mode is same to the one of mode. 3.4. Operation mode V The put current commutates to the diodes D and D 3 from the capacitors C and C. The put current is expressed by i _V (t) = -i _ (t-t/). The amplitude of the put current and the put power factor are determed by the parameters that are used for the resonance; capacitors C, C and ductor L and voltage ratio V. Hence the tended put impedance of the AC-DC converter can be obtaed by a designg these parameters properly. However, the design method is omitted this paper because of space limitation.
V. Simulation Results of the Proposed AC-DC Converter n this chapter, the simulation result of the proposed AC-DC converter is shown. Table presents the simulation conditions. n the simulation, the rated power is assumed as kva because the wireless power transmission systems are expected to apply to the EV charger. Fig. 5 presents the simulation waveforms of the proposed AC-DC converter. t is confirmed that the rectifier output voltage and chopper current i ch track to the each reference value. Thus, the bidirectional boost chopper is operated normally accordg to the P control. Moreover, a susoidal put current and unity put power factor are achieved. n this simulation, the put impedance is calculated from the fundamental component of the put voltage and put current as 5 j. with usg (9), where V _st is the fundamental component of the put voltage, _st is the fundamental component of the put current and is the phase angle between the put voltage and put current of the fundamental component. V_ st V_st Z cos j s (9) _st _st t means that the proposed converter is capable of the put impedance matchg to the 5 j at a reflection coefficient of.% which is defed by Z Z PR Z Z P (), F where Ż is the characteristic impedance, P F is supplied travellg power to the AC-DC converter, P R is the reflected power which occurs at the put termal of the AC-DC converter. Note that the reflection coefficient is used widely a research field of high-frequency circuits to evaluate the circuit performance. The squared reflection coefficient means the ratio of reflected power to the travelg power. n this paper, the put impedance is matched to a 5 j because it is most common impedance, although the put impedance of the proposed circuit can be matched to other tended impedances. Table : Simulacion conditions. tems nductors Capacitors L L C, C C 3 C 4 C 5 Value 55 nh.3 mh 38 pf 94 nf mf mf nput voltage v 4-4 nput current i - Chopper voltage 35. 349.8 Chopper current i ch -.4 V. Experimental Results of the Proposed AC-DC Converter Experimental verifications are shown this chapter. Table provides the circuit parameters for the experimental setup. Note that, the silicon carbide schottky barrier diodes (SiC-SBDs) are used the rectifier because rectifyg diodes are required to have a performance to rectify the 3.56 MHz AC. Besides, the design method of the resonance parameters, which affects the put impedance, is omitted this paper due to the page limitation. 5. -.8-3... Time t [msec] Fig. 5. Simulation result of the proposed AC-DC converter. vch ich vch * ich *.3
Table : Parameters of the circuit components. tems Manufactures Model number Value MOSFET S, S Vishay RFBN5APBF 5 V, A Diode D- Cree D86A 6 V, 8 A nductor L TDK VLF4T-R5N8R9 (Remodeled) 95 nh L - -.3 mh C, C TDK 6CGJ5JT 5 pf Capacitor TDK CKG57NX7RJ474M C4 nichicon UPWVMRD 47 nf ( parallel) mf ( parallel) C5 BHC Components ALS3ADB45 mf 5.. Fundamental characteristics Fig. 6 shows the experimental waveforms of the proposed AC-DC converter. t is clear that power conversion from 3.56 MHz to DC is achieved by the proposed converter with the susoidal put current and unity put power factor. Fig. 7 presents the harmonics analysis results of the put voltage and current which is conducted order to derive the put impedance from the experimental waveforms shown Fig. 6. Note that, the probes; a differential probe (Tektronix, P55) and a current probe (Tektronix, TCP3), which are used these experiments provide a limitation to the frequency bandwidth at MHz. For this reason, the harmonics components over 7 th are considered as reference values. From the calculation with (9), the put impedance is calculated as 9.6 j.5. The put impedance cludes the non-negligible error on the real part. This is attributed to the parasitic capacitances of the SiC-SBDs. n the next subsection, the proposed circuit is improved order to achieve tended put impedance. Fig. 8 shows the reason of the error on the put impedance. n a high frequency region, the parasitic capacitances C p-4 of the diodes cannot be ignored. Especially, an effect of the parasitic capacitance creases when a reverse voltage of the diodes is high. The parasitic capacitances make a leakage current path durg the operation modes and. Owg to the leakage current path, the put current is separated to the primary current path and the leakage current path. Thus the relation between the resonance capacitance C and the put impedance is different from the tended one. The combed capacitance on the upper arm is composed by the parasitic capacitances and additional capacitors. By contrast, the lower arm has only parasitic capacitances. Thus the current flowg through the upper and lower arms becomes unbalanced. t means that the design procedure of the nput voltage v [5V/div] nput current i [A/div] nput voltage [p.u.] - - -3 Rectifier output voltage [5V/div] Output voltage V B [V/div] 4[nsec/div] Fig. 6. Experimental waveforms of the proposed AC-DC converter. nput current [p.u.] - - -3 3 5 7 9 3 5 7 9 Number of harmonics Fig. 7. Harmonics analysis of the put voltage and put current of the proposed AC-DC converter.
resonance capacitance C is complicated. n order to solve the above-mentioned problem, the improved AC-DC converter is newly proposed the next subsection. 5.. mprovement of impedance matchg characteristics Fig. 9 shows the improved AC-DC converter with an put impedance matchg. Additionally, Table provides the circuit parameters for the experimental setup with the improved AC-DC converter. The two resonance capacitors; C 6 and C 7 are added to the lower arm the purpose of balancg the impedances between the upper arm and lower arm. Owg to these additional capacitors, the put impedance can be designed by considerg the parasitic capacitances easily because the put current is shunted equally to the each arm the mode. Fig. presents the operation modes of the improved AC-DC converter. The operation modes of the improved AC-DC converter are similar to the one of the AC-DC converter without an improvement. The difference between the Fig. 3 and Fig. is the resonance current path the modes and. The put current is divided to the path through an upper arm (L, C, C ) and the path through a lower arm (L, C 6, C 7 ). For this reason, the relationship between the circuit parameters and put impedance has changed. n this paper, the parasitic capacitances of the diodes are used as the capacitors C, C, C 6 and C 7. Thus, the resonance ductance is changed from 95 nh to.5 mh. Fig. presents the operation waveforms when the parasitic capacitance is used as a resonance capacitor. The DC output is obtaed from an 3.56-MHz AC. Additionally, it is clarified that the susoidal put current and unity put power factor are obtaed. Fig. shows the harmonic analysis results with the improved AC-DC converter. The put current total harmonic distortion (THD) of 8.% is achieved with the bandwidth up to th. A THD with the improvement is suppressed by 7.7% compared with the one without improvement. n addition, the put impedance is calculated S D C C p D C C p v i L D 3 i cu C p3 D 4 i cv C p4 v cv C 3 Ż v i D D i c C C L C 3 C 4 i ch L S C 5 v conv V B 3.56 MHz C 6 C 7 D 4 Leakage current path Fig. 8. Effect of the parasitic capacitances the mode. D 3 D 4 Fig. 9. mproved AC-DC converter with put impedance matchg. Table : Parameters of the circuit components the improved AC-DC converter. MOSFET Diode nductor tems Manufactures Model number Value S, S L Vishay RFBN5APBF 5 V, A Cree D86A 6 V, 8 A TDK D- VLF4T- R5N8R9.5 mh L - -.3 mh D C i i L du i cu v D C vcv i dv i cv C6 C7 Mode i v D i L du C D C vcv i cu i dv i cv C6 C7 Mode C-, C6-7 - (Parasitic capacitances of the diodes) (34.3 pf) i D C i L du i cu D C v cv i dv i cv i v D i L du C D i cu i dv C vcv i cv Capacitor TDK CKG57NX7RJ474M C4 nichicon UPWVMRD C5 BHC Components ALS3ADB45 47 nf ( parallel) mf ( parallel) mf v C6 Mode C7 C6 Mode V Fig.. Operation modes of the improved AC- DC converter. C7
nput voltage v [5V/div] nput current i [A/div] Rectifier output voltage [5V/div] Chopper current i ch [.5A/div] nput current [p.u.] nput voltage [p.u.] - - -3 - - -3 as 5.7 - j.. The reflection coefficient, which is calculated by (9), is =.6%. The reflection coefficient is used to evaluate a matchg characteristic of the high-frequency circuit the research field related to high-frequency circuit. f the impedance matchg is completely held, the reflection coefficient is zero. t means that the ratio of the reflected power which occurs at the put of the circuit to the travellg power is lesser than.%. t is clarified that the proposed AC-DC converter suppresses the reflected power from the above experiments. Thus, the proposed circuit can be applied to the receivg side of the wireless power transfer system. 5.3. Comparison of the reflection coefficient n this subsection, the reflection coefficients are compared among the conventional C-DBR, proposed converter without the improvement and the proposed converter with the improvement. Generally, the put impedance matchg of the C-DBR is not achieved the reason of the distorted put current and low put power factor. Moreover, the reflection coefficient of the conventional C-DBR depends on the load conditions and a smoothg capacitor widely. n contrast, the reflection coefficient of the proposed circuit does not depend on the load condition and a value of the smoothg capacitor. Fig. 3 shows the comparison result of the reflection coefficient which is calculated from () among the conventional C-DBR and the proposed AC-DC converters. Note that the conventional C- DBR has a smoothg capacitor of.47 mf. The proposed converter with the improvement and one without the improvement achieve the put impedance matchg with the reflection coefficients of.6% and 9.3% respectively. t is clear that the reflection coefficient can be suppressed compared to the conventional C-DBR. n particular, the reflection coefficient with the improved AC-DC 5 Without improvement converter suppresses the reflection coefficient by (Fig. ) 4 94.5 % compared with the conventional C-DBR With improvement (Fig. 9) with a load of 5. 3 V. Conclusion 4[nsec/div] Fig.. Operation waveforms of the improved AC-DC converter. This paper discussed the AC-DC converter which converts power from 3.56-MHz AC to DC for a receivg side of a wireless power transfer system with a susoidal put current. The wireless power transfer systems are required Reflection coefficient [%] 3 5 7 9 3 5 7 9 Number of harmonics Fig.. Harmonics components of the put voltage and put current the improved AC- DC converter. 5 33.3 5 Proposed circuit Conventional C-DBR Fig. 3. Comparison of the reflection coefficient between the conventional C-DBR and proposed circuit.
to operate high-frequency such as 3.56 MHz order to achieve a high power density of transmittg coils. Thus, the AC-DC converter the receivg side is required to operate at highfrequency. n such high-frequency region, the reflected power occurs when the put impedance is not matched to the characteristic impedance of the transmission le. n other words, the put impedance of the AC-DC converter needs to have the same impedance to the characteristic impedance of transmission les. n order to overcome the above-mentioned problem, two AC-DC converters are proposed and experimentally tested. The both AC-DC converters achieve the put impedance matchg without high-frequency switchg devices except the diodes with a simple configuration. The experimental results confirmed that the proposed converter with the improvement enable a conversion from 3.56- MHz AC to DC with the susoidal put current. From the experimental results, one of the proposed converters has an error on the real part of the put impedance. n order to improve this problem, the second converter is proposed. The proposed converter has two additional capacitors compared to the AC-DC converter without the improvement. The experimental results confirmed that the put impedance of 5.7 - j. is achieved. t means that the reflection coefficient is suppressed by up to 94.5 % comparison with the conventional diode bridge rectifier with a load of 5. References [] J. J. Casanova, Z. N. Low, J. L: A Loosely Coupled Planar Wireless Power System for Multiple Receivers, EEE Trans. On ndustrial Electronics, Vol. 56, No. 8, pp. 36-368 (9) [] S. A. Adnan, M. Am, F. Kamran: Wireless power transfer usg microwaves at.45 GHz SM band, BCAST 9, pp. 99- (9) [3] A. Karalis, J. D. Joannopoulos, M. Soljacic: Efficient Wireless non-radiative mid-range energy transfer, Annals of Physics, Vol. 33, No., pp. 34-48 (8) [4] A. Kurs, A. Karalis, R. Moffatt, J. D. Joannopoulos, P. Fisher, M. Soljacic: Wireless Power Transfer via Strongly Coupled Magnetic Resonances, Science, Vol. 37, pp. 83-86 (7) [5] S. Lee, R. D. Lorenz: Development and Validation of Model for 95%-Efficiency -W Wireless Power Transfer Over a 3-cm Air-gap, EEE Trans. On ndustry Applications, Vol. 47, No. 6, pp. 495-54 () [6] Y. Suh, K. Chang: A High-Efficiency Dual-Frequency Rectenna for.45- and 5.8-GHz Wireless Power Transmission, EEE Trans. On Microwave Theory and Techniques, Vol. 5, No. 7, pp. 784-789 () [7] L. Chen, S. Liu, Y. C. Zhou, T. J. Cui: An Optimizable Circuit Structure for High-Efficiency Wireless Power Transfer, EEE Trans. On ndustrial Electronics, Vol. 6, No., pp. 339-349 (3) [8] A. P. Sample, D. A. Meyer, J. R. Smith: Analysis, Experimental results, and Range Adaptation of Magnetically Coupled Resonators for Wireless Power Transfer, EEE Trans. On ndustrial Electronics, Vol. 58, No., pp. 544-554 () [9] Y. Hori: Future Vehicle Society based on Electric Motor, Capacitor and Wireless Power Supply, PEC, pp. 93-934 () [] S. Cheon, Y. Kim, S. Kang, M. L. Lee, J. Lee, T. Zyung: Circuit-Model-Based Analysis of a Wireless Energy-Transfer System via Coupled Magnetic Resonances, EEE Trans. On ndustrial Electronics, Vol. 58, No. 7, pp. 96-94 () [] J. R. Long: Monolithic Transformers for Silicon RF C Design, EEE Trans. On Solid-state Circuits, Vol. 35, No. 9, pp. 368-38 () [] K. Kusaka, J. toh: Experimental Verification of Rectifiers with SiC/GaN for Wireless Power Transfer Usg a Magnetic Resonance Couplg, EEE 9th PEDS, pp. 94-99 () [3] B. Sgh, B. N. Sgh, A. Chandra, K. Al-Haddad, A. Pandey, D. P. Kothari: A Review of Sgle-Phase mproved Power Quality AC-DC Converters, EEE Trans. On ndustrial Electronics, Vol. 5, No. 5, pp. 96-98 (3) [4] K. Matsui,. Yamamoto, K. Ando, G. Erdong: A Novel High DC Voltage Generator by LC Resonance Supply Frequency, EPE7, pp. -8 (7)