Journal of the Magnetics Societ of Japan J-STAGE Advanced Publication Date:6..6 capacitance connected in series with the feeding coil is given as foll

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1 Journal of the Magnetics Societ of Japan J-STAGE Advanced Publication Date:6..6 Reduction of Magnetic Field from Receiving Side b Separated in Contactless Charging Sstems for Moving Electric Vehicle S. Aoki, F. Sato *,**, S. Miahara *, H. Matsuki *, and T. Takura *** Graduate School of Engineering, Tohoku Univ., Aramaki-aa Aoba, Aoba-ku, Sendai, Miagi Japan * Graduate School of Biomedical Engineering, Tohoku Univ., Aramaki-aa Aoba, Aoba-ku, Sendai, Miagi Japan ** School of Engineering, Tohoku Gakuin Univ., -3- Chuo, Tagajo, Miagi Japan *** School of Engineering, Tohoku Institute of Tech., 35- Kasumi-cho, Taihaku-ku, Sendai, Miagi Japan Two main obstacles to the wider adoption of electric vehicles are short cruising distances and long charging times. We have proposed contactless charging sstems for moving electric vehicles utiliing electromagnetic induction. A problem in these sstems is high level magnetic field spreading far and wide from feeding and receiving coils, which can affect electronics and human health. In our previous work, we proposed a new feeding coil shape (multipolar coil) that reduced magnetic field at a distance b over 9%. In this paper, to reduce magnetic field from the receiving coil, we newl propose a separated receiving coil and compare it with a conventional spiral receiving coil. Simulations and power transmission eperiments revealed that the separated coil greatl reduced the magnetic field far from the coil and achieved high power transmission efficienc of over 8%. Ke words: Contactless charging sstem, Electric vehicle, Magnetic fields. Introduction. Contactless Charging Sstems for Moving Electric Vehicles Recentl, electric vehicles (EVs) have attracted attention as environmental awareness has grown. Current EVs have problems such as short cruising distances and long charging times. These problems have prevented EVs from becoming more widespread. To solve these problems, we have proposed contactless charging sstems for moving EVs and have performed various investigations ),). These sstems are able to transfer power from feeding coils in the road to a receiving coil on the underside of the EV b utiliing electromagnetic induction, which makes it possible to increase cruising distances without reling on batter capacit. Figure shows a schematic diagram of a contactless charging sstem for moving EVs. These sstems consist of an AC source, compensation circuits, feeding coils, a receiving coil, matching circuits, rectifiers, and a load (a batter or motor). The shape of the feeding coils is different from that of the receiving coil, and the sie is larger in order to deliver stable magnetic coupling and transmission power 3). Feeding AC Source Load (Batter or Motor) Rectifier, Converter Matching Circuit Compensation Circuit Recieving Fig. Contactless charging sstems for moving EVs. Electromagnetic Induction Figure shows a circuit diagram of contactless charging sstems that utilie electromagnetic induction. In this figure, the resistances r and r are wire-wound resistors, Pin is input power to inverter, Pout is load power and the capacitances connected in series and parallel with the receiving coil are load matching capacitances. These capacitances enable power to be transmitted at maimum efficienc ). The maimum efficienc, η ma, is determined b the coupling factor k and the qualit factors Q and Q of the coils. Using these parameters, the performance factor α is defined as follows ). B using α, η ma can be epressed as ) The values of the load matching capacitances C s and C p can be written as ) ma C s R k C p r Figure 3 shows the relationship between η ma and the performance factor α. High transmission efficienc is required to achieve high α. To compensate for the power factor, the value of the ( r ( Q Q Q R R r ) ( ) ) () () (3) (4) doi:.3379/msjmag.6r5 JOI:JST:JSTAGE/msjmag/6R5

2 Journal of the Magnetics Societ of Japan J-STAGE Advanced Publication Date:6..6 capacitance connected in series with the feeding coil is given as follows: C (5) L Feeding side Receiving side (Load) Fig. Circuit diagram for contactless charging sstems utiliing electromagnetic induction Maimum efficienc [%] Fig. 3 Relation between α and maimum efficienc the feeding loop in order to cancel out the magnetic field from the feeding loop. When the multipolar coil is used, the majorit of the magnetic field from the combined feeding and receiving coil sstem is generated from the receiving coil. It is therefore necessar to reduce the magnetic field from the receiving coil in order to reduce the magnetic field from the overall sstem. In this article, we propose a new shape of receiving coil with the aim of reducing magnetic field from the receiving coil and we compare the proposed coil with a conventional spiral (Traveling Direction) Feeding Loop Loops for Offsetting Magnetic Field (Misalignment Direction) Current Path of Each Loops We propose a new shape of coil which we call the separated.3. Magnetic Field from Feeding and Receiving s As shown in Fig., the feeding coils are larger than the receiving coil in order to ensure stable magnetic coupling and to suppl stable power along the direction of travel 3). The sie of the feeding coils in the direction of travel is 5 to m. Hence, the magnetic coupling factor, k, is assumed to be less than., meaning that high-level magnetic fields are generated from the feeding and receiving coils. The magnetic field can affect electronics and human health to a distant place. It is therefore necessar to reduce the magnetic field from these coils. Man studies have investigated reduction of magnetic field from contactless charging sstems 5),6). In previous work, we proposed a new shape of feeding coil (multipolar coil) which is able to reduce the magnetic field at a distance b over 9% compared with that of conventional rectangular coils 7). The multipolar coil consists of a feeding loop at the center of the coil and two loops for offsetting the magnetic field on both sides of the feeding loop as shown in Fig. 4. The loops for offsetting coil. Figure 5 shows the structure of the separated coil. In this coil, the cross coil which has been proposed for contactless charging sstems 8),9) is split into two coils that are connected differentiall. B using this configuration, the magnetic field from both coils is canceled out, reducing the magnetic field at a distance. A high coupling factor between the feeding and receiving coils can be ensured b adjusting the spacing between both coils. In this stud, we define the distance between the two coils as the parameter. Figure 6 shows the configuration and sie of the separated coil and spiral coil that were used as receiving coils in this stud. The lit wire used in both coils consists of 3 strands of. mm thick wire, and a Mn-Zn ferrite plate with a relative permeabilit is 4 is placed inside the separated coil and behind the spiral coil in order to increase the inductance. Table shows the electrical properties of the separated coil and spiral coil at kh as measured with an LCR meter (E498A, Agilent Co.) when was mm, mm, and 5 mm. As can be seen in the table, a high qualit factor Q was confirmed as the parameter was increased because this the magnetic field are ecited in the opposite phase to decreased the mutual inductance and increased the coil. Fig. 4 Multipolar coil for reducing leakage magnetic field from the feeding coil.. Proposal of Separated. Separated doi:.3379/msjmag.6r5 JOI:JST:JSTAGE/msjmag/6R5

3 Journal of the Magnetics Societ of Japan J-STAGE Advanced Publication Date:6..6 self-inductance. 6 mm Cross Divide into Two s Separated Series Connection :Magnetic field direction :Current path Fig. 5 Structure of separated coil Separated : 6 Turns 3 mm 6 mm Spiral : 5 Turns 6 mm mm 5 mm Series Connection Ferrite Fig. 6 Configuration and sie of separated coil and spiral coil Table Electrical properties of the receiving coils (frequenc: kh) Separated.. Comparison of Magnetic Field Generated from Receiving s Turns 6 Spiral 5 [mm] L [μh] r [mω] Q First, in order to indicate magnetic field structures of separated coil and spiral coil, we analed flu lines generated from each coils. Figure 7-(a) shows the simulation models and analsis plane (- plane). Figure 7-(b) shows the analsis results. The ecitation condition is a current of A. In Fig.7 (b), we used Mawell D electromagnetic field analsis software (ANSYS Co.) to anale the flu lines and the value of vector potential. As shown in the Fig. 7-(b), the separated coils ehibit a 4-pole structure and their flu lines concentrate in near the coils compared with that of the spiral coil. As the parameter increases, the magnetic flu near the coil increases without the 4-pole structure changing. This characteristic makes it possible to reduce the magnetic field far from the coil and to increase interlinkage flu through the feeding coil and the coupling factor between the feeding coil and receiving coil. Net, Fig. 8 shows comparison results for magnetic flu densit at m from the center of the coil on the -, -, and -aes (as shown in Fig. 8-(a)). In Figure 8-(b), the value of flu densit was calculated b Mawell 3D electromagnetic field analsis software (ANSYS CO.) The ecitation condition is a current of A and a frequenc of kh. In Fig.8-(b), the magnetic flu densit far from the separated coils smaller than that from the spiral coil. The magnetic flu densit from the separated coil with = mm was lower b 73% on the -ais, 86% on -ais, and 93% on the -ais. This shows that the separated coil reduces the magnetic field at a distance from the receiving coil. 3 m Fig. 7 (a) Simulation models and analsis plane Separated = mm 3 m [Wb/m] [Wb/m] Spiral (b) Magnetic flu lines on the - plane [Wb/m] Simulation models and flu lines on the - plane doi:.3379/msjmag.6r5 JOI:JST:JSTAGE/msjmag/6R5

4 Journal of the Magnetics Societ of Japan J-STAGE Advanced Publication Date: m (Traveling Direction).5.5 Flu densit [nt] (a) Simulation models and compared points Receiving Separated = mm ais 7 mm Spiral -ais -ais -ais (b) Comparison of magnetic flu densit at m on the -, -, and -ais Fig. 8 Simulation models and comparison of magnetic flu densit at m on the -, -, and -ais.3 Coupling Coefficient between the Feeding and Receiving s We measured the coupling coefficient between the feeding and receiving coils when the separated coil ( = mm, mm, and 5 mm) and spiral coil were used as the receiving coil. Figure 9 shows the configuration of the measurement model. The feeding coil is a multipolar coil (length: 5 m; width:.6 m; number of loops: turn). The gap between the feeding and receiving coils was set to 7 mm. Figure shows coupling factor versus location of the receiving coil along the direction of travel. The measurement results indicate that the coupling coefficient increased with increasing. This is due to an increase in the interlinkage flu as mentioned in Section., and also due to the change in relative distance between the feeding and receiving coils. The coupling coefficient was.35 for, which is comparable to the value for the spiral coil, and was.6 for. This shows that it is possible to achieve high transmission efficienc while reducing the magnetic field b using a separated coil as the receiving coil. (Misalignment Direction) (Traveling Direction) Feeding Coupling factor k (Misalignment Direction) Separated = mm Spiral Spiral Traveling direction [m] Fig. Coupling factor along the direction of travel 3. Transmission Eperiment and Evaluation of Magnetic Field 3. Transmission Eperiment We conducted transmission eperiments using separated coils ( = mm, mm, and 5 mm) and a spiral coil as the receiving coil, and measured the transmission efficienc. The input power to the inverter was fied at W and the frequenc was kh. Table shows the electrical properties of the feeding coil (multipolar coil). A resistance load ( Ω) was connected after the secondar load matching capacitances (Fig. ). Figure shows the transmission efficienc along the direction of travel. The transmission efficienc at the center of the feeding coil was 8.% when a separated coil with = mm was used, and was 88.% for. We thus confirmed that a contactless charging sstem with a high transmission efficienc can be constructed b using a separated coil as the receiving coil. Table Electrical properties of the feeding coil (frequenc: kh) Multipolar Turns of each loop L [μh] r [mω] Q Fig. 9 Feeding and receiving coils doi:.3379/msjmag.6r5 JOI:JST:JSTAGE/msjmag/6R5

5 Journal of the Magnetics Societ of Japan J-STAGE Advanced Publication Date:6..6 Transmission efficienc [%] (Misalignment Direction) Separated = mm.5 m (Traveling Direction) Spiral Traveling direction [m] Fig. Transmission efficienc along the direction of travel 3. Evaluation Magnetic Field from Feeding and Receiving s during Transmission We analed the magnetic field surrounding coils during transmission and evaluated the separated coil compared to a spiral coil. Table 3 shows the estimated current values when the load power is kw (b means of circuit analsis). We also analed the magnetic field from the feeding and receiving coils b Mawell 3D in terms of current values. Figure shows the distribution of magnetic flu densit from feeding and receiving coil. Figure-(a) is the distribution in the -direction, (b) is in the -direction and (c) is in the -direction. As shown in Figure, flu densit when the separated coil was used as the receiving coil is lower than spiral coil as it goes awa farther from center of coil. And Figure 3-(b) shows the result of comparing the magnetic flu densit at m from the center of the coil on the -, -, and -aes (as shown in Figure 3-(a)). The leakage magnetic field was reduced b 64% on the -ais, 8% on the -ais and 9% on the -ais compared to using a spiral coil when the separated coil with was used as the receiving coil. Receiving Separated Spiral Table 3 current ( kw class) [mm] I Feeding_coil [A] I Recieving_coil [A] Flu densit [μt] Flu densit [μt].e+5.e+4.e+3.e+.e+.e+.e-5. Distance from center [m] Flu densit [μt].e-.e-.e-3.e-4.e+5.e+4.e+3.e+.e+.e+.e-.e-.e-3.e-4 Separated = mm Spiral (a) Distribution of magnetic flu densit (-direction) Separated = mm Spiral.E-5. Distance from center [m] (b) Distribution of magnetic flu densit (-direction) Flu densit [μt].e+5.e+4.e+3.e+.e+.e+.e-.e-.e-3.e-4 Separated = mm Spiral.E-5. Distance from center [m] (c) Distribution of magnetic flu densit (-direction) Fig. Distribution of magnetic flu densit from (a) Simulation model and compared points.. Separated = mm Spiral. -ais -ais -ais (b) Comparison of magnetic flu densit (at m from center of feeding coil) Fig.3 Comparison of magnetic flu densit doi:.3379/msjmag.6r5 JOI:JST:JSTAGE/msjmag/6R5

6 Journal of the Magnetics Societ of Japan J-STAGE Advanced Publication Date: Summar In this stud, we eamined the magnetic field from the receiving coil in contactless charging sstems for moving EVs. This paper newl introduced the concept of the separated coil for use as the receiving coil, and compared it with a conventional spiral coil The results of analses and eperiment showed that the magnetic field far from the coil can be reduced b approimatel 9% and high transmission efficienc can be obtained b means of adjusting the parameter. In future work, it is necessar to identif the magnetic field when the receiving coil is fitted to an EV and to reduce further magnetic field b using magnetic shielding such as aluminum sheet. References ) T. Takura, A. Aruga, F. Sato, T. Sato, H. Matsuki EVTeC and APE Japan Conference Proceedings 448 pp.-7 (4) ) T.Misawa, T.takura, F.Sato, and H.Matsuki : IEICE Technical Report WPT-33, pp3-8 () (in Japanese) 3) N.Aruga, Y.Ota, Y.Imamura, S.Sato, and H. Matsuki: J.Magn.Soc.Jpn., 39, No.3, pp.-5 (5) 4) T.Takura, Y.Ota, K.Kato, F.Sato, and H.Matsuki J. Magn. Soc. Jpn., 35,pp. 3-35,() 5) J.Shin, B.Song, S. Chung, Y.Kim, G.Jung and S.Jeon :IEEE Wireless Power Transfer (WPT), pp (3) 6) D.Narita, T.Imura, H.Fujimoto, Y.Hori: IEICE Technical Report WPT4-3, pp39-44 (4) (in Japanese) 7) S.Aoki, F.Sato, S.Miahara, H.Matsuki, and T.Takura:IEICE Technical Report WPT5-8, pp43-48 (5) (in Japanese) 8) Y.Kaneko, N.Ehara, T.Iwata, S.Abe, T.Yasuda, K.Ida: IEEJ Trans. IA, Vol.3,No.6,pp () (in Japanese) 9) H.Yamaguchi, T.Takura, F.Sato, and H.Matsuki: J.Magn.Soc.Jpn., 38, No.- pp (4) Received Oct. 6, 5; Revised Nov. 4, 5; Accepted Dec. 4, 5 doi:.3379/msjmag.6r5 JOI:JST:JSTAGE/msjmag/6R5