Wireless Charging Research Activities Around the World [Society News]

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  • 30 IEEE PowEr ElEctronIcs MagazInE zJune 2014

    PELS members, including those who are unable to attend the conferences. As a result, there will be a monthly Webinar series geared toward students and young professionals. The topics will include both technical and non-technical content ranging from hard-ware prototyping tips to finding a good job or a mentor. Some of the best pre-sentation winners at major power elec-tronics conferences will also be invited to present their work to the wider PELS

    audience. This will help the younger PELS members gain more exposure and experience.

    As the activities for young mem-bers have grown, so has the Student and Young Professional Committee. The current members include Texas Instruments Pradeep Shenoy, Kath-erine Kim from the University of Illinois at Urbana-Champaign, Jenn Vining from Daimler, and Lingxiao Xue from Virginia Tech.

    There is still more room for growth, and the committee is encour-aging students and young profession-als to get involved in organizing new activities for young PELS members. If you are interested in participating, please check out the PELS Young Pro-fessionals Web page at http://www.ieee-pels.org/membership/pels-gold. The committee is always looking for feedback or suggestions, so please contact PELS if you have any ideas.

    The latest research activities in wireless charging from re-search and development (R&D) centers around the world are highlighted here. Driven by plug-in electric vehicles (EVs) and consumer electronics, wireless charging is gain-ing momentum at research centers worldwide. To get a glimpse of what is happening at various centers, Burak Ozpineci, group leader of Oak Ridge National Laboratorys (ORNLs) Power Electronics and Electric Machinery Group, contacted a few researchers. What follows is a summary of the re-sponses to his survey.

    Department of Electrical and Computer Engineering, University of Auckland, New ZealandProf. Grant Covic reported that his group has worked on wireless charging

    technology since 1989 and is a leader in the field of high-power resonant induc-tive power transfer with applications in industry and EV wireless charging. They pioneered the means to control power via decoupling of the secondary (enabling multiple secondary wind-ings to be powered on one primary system seamlessly). In addition, his group claims to have developed much of the early mathematics describing modes of resonance and bifurcation phenomena when variable-frequency supplies were in use to ensure effi-cient operation. Also, they proposed many unique secondary controllers and magnetic designs for material-handling applications and automated guided vehicles relative to single and multiphase tracks to enable efficient power transfer with wide tolerance to movement.

    Since the mid-1990s, Prof. Covics group has also pioneered various lumped low-loss (high quality fac-tor) single and multicoil magnetic

    designs for EV charging of people movers (specially designed to have single-sided fields with low leak-age). More recently, in the late 2000s, researchers focused on single and multiphase designs to trans-fer energy wirelessly on roadways and provide both motive power and charging to moving vehicles. The designs enable highly efficient power transfer with wide tolerance and low leakage, and all are able to work seamlessly with proposed stationary charging systems. These designs are already being used or evaluated for buses and cars by com-mercial partners and, more recently, are being scaled back for use in low-power applications.

    According to Prof. Covic, the de-partment holds patents for innova-tions in efficient power-supply design; magnetic couplers, including the first intermediate coupler for EV highways proposed in the early 1990s; and sec-ondary side controllers. Following

    Digital Object Identifier 10.1109/MPEL.2014.2319511 Date of publication: 20 June 2014

    wireless charging research activities around the world

  • Tesla, all of the groups designs are highly resonant, being tuned to reso-nance at or near the operating frequen-cy of choice. Covic stated, We see no difference between inductive power transfer systems that we and others have developed since the early 1990s and the recently proposed strongly coupled magnetic resonance systems, both of which are tuned for resonance, have native high-Q coils for low loss, and operate in the near-field coupling regions. (See reasons in [1].)

    The licensees who have commer-cialized its designs include: material-handling giant Daifuku in

    Japan [which has sold more induc-tive power transfer systems (IPTSs) than all other systems sold in any other field globally, with sales of over US$500 million annually] in material-handling and clean room systems (for silicon chip and LCD/LED screen manufacture)

    Qualcomm USA in roadway-pow-ered EV (RPEV) charging, Conduc-tix-Wampfler (now IPT Technology) in material handling and bus charg-ing, Power-by-proxi in small appli-ances and slip-ring applications 3i-innovation in roadway lighting.

    There are many other projects still in development. Two invited papers that present Prof. Covics work are [1] and [2].

    Utah State University: Power Electronics LabProf. Zeljko Pantics research includes: the design of nonpolarized and

    bipolar magnetic couplers with advanced field-shaping and power-transfer capabilities research of intelligent remotely tuned

    recharging systems for autonomous in-motion charging applications the use of active rectifiers with mul-

    tiangle control to improve efficiency

    over a wide range of operating con-ditions and for bidirectional opera-tion of wireless power systems multicoil omnidirectional wireless

    power systems for biological implants.Past accomplishments include:

    WAVE, Inc. (where WAVE stands for wireless advanced vehicle elec-trification) a Utah State University technology spin-out company. Dual-side control for 90% efficien-

    cy (grid to battery) of a 5-kW inductive charging system for EVs for a wide range of coupling and loading conditions. WAVE, in partnership with Utah

    State Universitys Energy Dynamics Labs (now called Power Elecronics Lab or UPEL), developed the first solid-state 50-kW wireless power transfer (WPT) stationary charging system in North America for bus transit (Figure 1).

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  • 32 IEEE PowEr ElEctronIcs MagazInE zJune 2014

    Utah State University is building an EV systems integration facility and 1/4-mi electrified track on the cam-pus for stationary and in-motion WPT research and demonstration. The anticipated completion date is October 2014 (Figure 2).A partial list of published papers in

    the field is [3][5].

    Korea Advanced Institute of Science and Technology: Tesla Lab

    5-m and 7-m off-long-Distance IPtss Using optimum-shaped Dipole coilsAn extremely loosely coupled IPTS for extremely long-distance WPT

    using optimum-shaped dipole coils has been developed by a team led by Prof. Chun T. Rim at the Korea Ad-vanced Institute of Science and Technology (KAIST) since 2012. In 2012, his team designed and verified by experiments a 209-W prototype over a 5-m distance. The coupled magnetic resonance system (CMRS), first developed by a Massachusetts Institute of Technology team, had a recorded 2.2-m distance wireless power delivery for 60 W. However, it suffers from hypersensitive charac-teristics due to the very high quality factor Q (~2,000) of bulky loop-type self-resonant coils. Moreover, a low-efficiency radio-frequency amplifier

    rather than a high-efficiency switch-ing converter was used due to the h igh operat ing f requency (13.65 MHz). For the primary and secondary coils, the KAIST team adapted the dipole-type coils of nar-row and long structure with ferrite cores to minimize the parasitic ef-fects and coil sizes. A conventional switching converter was used at the switching frequency of 20100 kHz. An optimum stepped core structure as well as a winding method was also proposed [6], [7]. Prof. Rim has recently identified the fact that the CMRS is just a special form of an IPTS [8], where the source and transmitting coils constitute a strongly coupled transformer, the load and receiving coils constitute another strongly coupled transform-er, and the transmitting and receiv-ing coils constitute a loosely coupled transformer. Therefore, it is no lon-ger necessary to consider the CMRS the only candidate for long-distance wireless power. This year, the KAIST team has successfully extended the distance of wireless power up to 7 m for consideration as an alternate power source for nuclear power plants during severe accidents.

    Ultraslim IPtss for rPEVsA stream of modern RPEVs is the on-line EV (OLEV), which has solved most of the problems of the first de-velopment of RPEV for the Partners for Advanced Transit and Highways (PATH) teams work. Since 2009, the OLEV has been developed by a re-search team led by KAIST [9]. Innova-tive coil designs and roadway construction techniques as well as the reasonably high operating fre-quency of 20 kHz, compared with the PATHs 400 Hz, made it possible to achieve a peak power efficiency of 83% at an output power of 60 kW with a large air gap of 20 cm and lateral tolerance of 24 cm [10]. Moreover, the power rail construction cost of the OLEV, which is responsible for more than 80% of the total deploy-ment cost for RPEVs, has been dramatically reduced to at least

    fig 2 Utah State University is building an EV systems integration facility and a 1/4-mi elec-trified track on campus for stationary and in-motion WPT research and demonstration. The anticipated completion date is October 2014. (Photo used courtesy of Utah State University.)

    fig 1 WAVE, in partnership with Utah State Universitys Energy Dynamics Labs (now called Power Elecronics Lab or UPEL), developed the first solid-state 50-kW WPT sta-tionary charging system in North America for bus transit. (Photo used courtesy of Utah State University.)

  • June 2014 zIEEE PowEr ElEctronIcs MagazInE 33

    one-third of that of the PATH team. The primary current has been also reasonably mitigated to as low as 200 A, and the onboard battery size has been significantly reduced to 20 kWh. In addition, a generalized im-proved magnetic mirror model (IM3) was developed for the design of coils with cores, and it can be used to ana-lyze the maximum magnetic flux den-sity on core plates for avoiding core saturation [11].

    Past accomplishments

    5-m and 7-m Off-Long-Distance IPTSs Using Optimum-Shaped Dipole CoilsThe long-distance IPTSs have been demonstrated at 209 and 11 W over 5 and 7 m, respectively, as shown in Fig-ure 3. An overview of the fabricated prototype is shown in Figure 4(a). Seriesparallel resonant circuits are used for the 7-m off-distance proto-type to achieve higher load voltage than the seriesseries scheme, which was used for the 5-m off-distance prototype. The simulation result on the normalized magnetic flux density of the stepped core and even core is shown in Figure 4(b), where the peak magnetic field in the even core is 47% greater than the stepped core.

    This research has been accom-plished by a KAIST research team led by Prof. Chun T. Rim, with financial support from the Korean government.

    PL(W)

    10 20 30 40

    (b)

    N2 = 10N2 = 20N2 = 30

    I1(A)

    14

    12

    10

    8

    6

    4

    2

    0

    PL(W)

    0 5 10 15 20 25

    (a)

    30 35 40

    3 m4 m5 m

    I1(A)45 50

    1

    0.1

    10

    100

    1,000

    10,000

    fig 3 The measured load power PL versus the primary RMS current I1 at 20 kHz for a (a) 5-m off-prototype (seriesseries resonant) [6] and (b) 7-m off-prototype (seriesparallel resonant) [7].

  • 34 IEEE PowEr ElEctronIcs MagazInE zJune 2014

    1G (Car) 2G (Bus) 3G (SUV) 3*G (Bus) 3*G (Train) 4G (Bus)

    Date27 February

    2009 14 July 2009 14 August 2009 31 January 2010 9 March 20102010~ (Under Development)

    Vehicle

    System Spec.Air-Gap = 1 cm

    Efficiency = 80%Air-Gap = 17 cmEfficiency = 72%

    Air-Gap = 17 cmEfficiency = 71%

    Air-Gap = 20 cmEfficiency = 83%

    Air-Gap = 12 cmEfficiency = 74%

    Air-Gap = 20 cmEfficiency = 80%

    EMF 10 mG 51 mG 50 mG 50 mG 50 mG < 10 mG

    20 cm 140 cm 80 cm 80 cm 80 cm 10 cm

    20 kg 80 kg 110 kg 110 kg 110 kg 80 kg

    55 # 18 # 4 cm3 160 # 60 # 11 cm3 170 # 80 # 8 cm3 170 # 80 # 8 cm3 170 # 80 # 8 cm3 80 # 100 # 8 cm3

    3 kW/Pick-Up 6 kW/Pick-Up 15 kW/Pick-Up 15 kW/Pick-Up 15 kW/Pick-Up 25 kW/Pick-Up

    Pick-Up

    Power

    Weight

    Size

    PowerRail

    (Width)

    fig 5 A summary of the developments of OLEV, including the IPTSs [9].

    Distance, 57 m

    Primary Coil

    (a) (b)

    Even

    Even

    Stepped

    -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5(m)

    Stepped

    46.7%

    B1.6

    1.4

    1.2

    1.0

    0.8

    0.6

    0.4

    0.2

    0.0

    fig 4 The fabricated prototype and optimum core structure design [6]: (a) an overview of a fabricated prototype and (b) a compar-ison between a stepped core and an even core.

  • June 2014 zIEEE PowEr ElEctronIcs MagazInE 35

    Ultraslim IPTSs for RPEVsAs shown in Figure 5, the first gener-ation (1G) was a concept demonstra-tion car of the OLEV, and the second generation (2G) was for OLEV buses. The third generation (3G) was for an OLEV passenger car and three OLEV trains (3+G) that have been successfully deployed at the Seoul Grand Park, Korea, since 2010. Two updated OLEV buses (3+G) were deployed at the 2012 Yeosu EXPO, Korea, and another two OLEV buses (3+G) have been in full operation at the main campus of KAIST since 2012. Recently, two OLEV buses (3+G) have been com-mercialized at the 48-km long-dis-tance route in Gumi, Korea.

    One of the problems found dur-ing the development of 2G OLEV was the inherently weak structure of the power-supply rail. As a remedy for this mechanical weakness, a bone

    structure core, as shown in Figure6, was suggested and registered as a pat-ent [12]. Figure 7 shows the W-type power-supply rail of the 3G OLEV [4] under road construction in (a) and under test in (b).

    Despite the large gap between cores, the generated...

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