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Selective Harmonic Elimination Method of RadiationNoise from Automotive Wireless Power Transfer

System Using Active Rectifier

Hongseok Kim, Seungtaek Jeong,Dong-Hyun Kim, and Joungho Kim

TeraByte Interconnection and Package LaboratoryKorea Advanced Institute of Science and Technology

Daejeon 305-701, Republic of KoreaEmail: [email protected]

Young-Il Kim and In-Myoung KimEnercons Co. Ltd.

Seoul 153-802, Republic of KoreaEmail: [email protected]

AbstractBecause wireless power transfer (WPT) systemsused in automotive vehicles are likely to cause electromagneticinterference (EMI) with sensors, antennas, and controllers, themagnetic near-field spectrum from a WPT system has to beinvestigated and controlled properly. In this paper, we proposea selective harmonic elimination (SHE) method of the radiationnoise from an automotive WPT system to reduce EMI causedby fast switching transitions of a resonant inverter and rectifierused for WPT systems. The simulated EMI spectra show that thesignificant reduction up to 30 dB in the harmonic componentscan be achieved by using the proposed SHE method.

I. INTRODUCTION

The automotive wireless power transfer (WPT) technologyusing magnetic field coupling has been actively researchedand developed until recently [1][4]. In automotive WPTsystems, the magnetic flux leakage inevitably exists aroundthe magnetically coupled coils due to relatively large air gap inbetween. The time-varying leakage magnetic field from a high-power WPT system increases the possibility of the potentialnoise issues related to the audio and radio systems becauseit consists of radio frequency (RF) spectral components withrelatively high amplitudes as shown in Fig. 1.

One major task in developing an automotive WPT systemis to control its electromagnetic interference (EMI) whilekeeping its efficiency as high as possible. In many WPTapplications, passive magnetic shielding structures are oftenused as a basic measure to reduce EMI and the resultant energylosses in adjacent conductors [2], [4]. However, the passiveshielding technique has its limits due to the finite values ofpermeability and conductivity and design requirements suchas weight and cost. A possible way to overcome such limitsis to reduce or mitigate the harmonic noise at its source(s).Typical methods include the frequency dithering and phase-shift control methods [5][7].

In this paper, we propose a novel selective harmonicelimination (SHE) method of the radiation noise from anautomotive WPT system to reduce possible EMI caused byhigh dv/dt of a resonant inverter and that of a rectifier.

TeraByte Interconnection and Package LaboratoryTERATeraByte Interconnection and Package Laboratory

Human Safety and Electromagnetic Interference (EMI) Issues of Automotive Wireless Power Transfer (WPT) SystemHuman Safety and Electromagnetic Interference (EMI) Issues of Automotive Wireless Power Transfer (WPT) System

AM/FM Radio Receiver500 kHz ~ 1.8 MHz (AM)

80 ~ 110 MHz (FM)

Radio Signal

9k 100k 1M 10M 30M20k

Frequency (Hz)

Typical EMI Spectrum

Mag

nitu

de(d

BV

)

Harmonics

FundamentalTransmitter

(20 kHz / 85 kHz)

-

+

Battery~ =

LeakageMagnetic Field

AC 50/60Hz

Fig. 1. A schematic of an automotive wireless power transfer system forelectric vehicle battery charging and its typical EMI spectrum. The operatingfrequency can be either 20 kHz or 85 kHz, and relatively intense leakagemagnetic field is produced around the magnetically coupled coils, containingthe fundamental and harmonic components of the operating frequency of thetransmitter.

II. CONVENTIONAL AUTOMOTIVE WIRELESS POWERTRANSFER SYSTEM

Fig. 2(a) shows the equivalent circuit model of the conven-tional automotive WPT system employing the series-series res-onance topology, and the class-D full-bridge inverter and rec-tifier [4]. The gate-control signals of the square-wave inverterand the simulated waveforms of the voltages and currents areshown in Fig. 2(b) and 2(c), respectively. ANSYS Simplorer isused for circuit simulation. The circuital parameters designatedin Fig. 2(a) and used in simulations are tabulated in Table I,where the parameter values are taken from [4] and fr is theseries resonance frequency (fr = 1/

L1C1 = 1/

L2C2).

The Fourier series expansions of the voltages VAB and VCDshown in Fig. 2(c) are ideally written as

VAB = Vdc4

n=1,3,5...

1

nsin (n0t) (1)

VCD = VL4

n=1,3,5...

1

nsin (n0t+ n) (2)


2

Conventional WPT System and Current Waveforms/SpectraConventional WPT System and Current Waveforms/Spectra

sinsin /2

Class-D Full Bridge Inverter(Square Wave Inverter)

Class-D Full Bridge Rectifier

C

D

Q3

Q2

A

B

Q4

Q3p,ctrl

Q2p,ctrlQ4p,ctrl

Q1p,ctrl Q1

D3

D2D4

D1D3

D2D4

D1

(a)


3

Conventional WPT System Using Square Wave InverterConventional WPT System Using Square Wave Inverter

Control Signals of Inverter Switches

Q1p,ctrl

01

2 3

01

2 3

Q2p,ctrl

Q4p,ctrl

Q3p,ctrl

01

2 3

01

2 3

(b)


4

Verification of Proposed Control Method Using Simulation :Comparison of Time-domain WaveformsVerification of Proposed Control Method Using Simulation :Comparison of Time-domain Waveforms

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1-200

-100

0

100

200

Time (ms)

Volta

ge (V

)

Voltage and Current Waveforms

-20

-10

0

10

20C

urre

nt (A

)

(c)

Fig. 2. A conventional WPT system, (a) An equivalent circuit model ofa conventional WPT system, (b) The gate-control signals of the invertergenerating the square wave voltage across the output terminals A and B, (c)The time-domain waveforms of inverter output voltage VAB, rectifier inputvoltage VCD, inverter output current ITx, and rectifier input current IRx. Fortransmitting 1-kW average power to the load, Vdc is set to be 104.3 V.

TABLE I. CIRCUITAL PARAMETERS

Parameter Value Parameter Value

R1 = R2 90 m VL 150 V

L1 = L2 682 H RL 22.5

M 98 H Cf 680 F 4C1 = C2 92.85 nF fr 20 kHz

where Vdc and VL are the dc source and load voltagesrespectively, 0 is the operating frequency of the inverter, and is the phase shift between VAB and VCD.

Equations (1) and (2) clearly show that the voltage wave-forms contain a large amount of odd harmonics resulting inRF spectral contents of the radiation noise.

III. PROPOSED AUTOMOTIVE WIRELESS POWERTRANSFER SYSTEM

The radiation noise is proportional, within a geometricfactor, to the total ampere-turns of the coil currents as follows.

~H d~L = N1ITx +N2IRx (3)

where N1 and N2 are the number of turns of the primary andsecondary coils, respectively, and ITx and IRx are the primary


5

Phase-shift ControlledActive Rectifier

C

D

D3p

D2p

A

BD4p

Q3p,ctrl

Q2p,ctrlQ4p,ctrl

Q1p,ctrl Q3p

Q2pQ4p

Q1p

D1pQ3s,ctrl

Q2s,ctrlQ4s,ctrl

Q1s,ctrlQ3s

Q2sQ4s

Q1s

D3s

D2sD4s

D1s

Phase-shift Controlled Inverter(Modified Sine Wave Inverter)

(a)


6

Q1p,ctrl

01

01

Q2p,ctrl

2 3

Q4p,ctrl

01

01

Q3p,ctrl

Control Signals of Inverter Switches

(b)


7

Q1s,ctrl

01

01

Q2s,ctrl

2 3

Q4s,ctrl

01

01

Q3s,ctrl

2 3 4

Control Signals of Rectifier Switches

(c)


8

Verification of Proposed Control Method Using Simulation :Comparison of Time-domain WaveformsVerification of Proposed Control Method Using Simulation :Comparison of Time-domain Waveforms

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1-200

-100

0

100

200

Time (ms)

Volta

ge (V

)

Voltage and Current Waveforms

-20

-10

0

10

20

Cur

rent

(A)

(d)

Fig. 3. The proposed automotive WPT system employing active rectifier andthe proposed phase-shift control scheme, (a) An equivalent circuit diagram,(b) The gate-control signals of the inverter generating the modified sinewave voltage across the output terminals A and B, (c) The gate-controlsignals for the proposed phase-shift controlled active rectifier producing themodified sine wave voltage across the input terminals C and D, (d) The time-domain waveforms of the voltages and currents in the case of = 60. Fortransmitting 1-kW average power to the load, Vdc is set to be 136.6 V.

and secondary coil currents, respectively.

Equation (3) simply shows that a harmonics of magneticfield can be selectively eliminated only by getting rid ofthe corresponding harmonic components of both ITx and IRx.Given the coil structure, certain harmonic components of thecoil currents can be selectively eliminated by removing thecorresponding harmonic components of both VAB and VCD.

To do so, we first propose a WPT system using the activerectifier and the phase-shift control in both the inverter and

rectifier as shown in Fig. 3. It is well known that certainharmonics of the inverter output voltage can be reduced oreliminated by using the phase-shift control method [8]. In thiscase, the output voltage spectral contents of the phase-shiftcontrolled inverter is

VAB = Vdc4

n=1,3,5...

1

nsin (n0t) cos

(n2

)(4)

where is the phase shift between the switching of the twolegs of the inverter as shown in Fig. 3(b).

If = 0, then (4) represents square wave voltage. Depend-ing on , the magnitudes of certain harmonic components ofVAB can be reduced to zero. However, the corresponding har-monic components of the magnetic field cannot be eliminatedunless the corresponding harmonic components of VCD are noteliminated simultaneously.

To eliminate the harmonic currents by VCD, we apply thephase-shift control scheme with the same control variable as the inverter into the active full-bridge rectifier as shown inFig. 3(a) and 3(c). The Fourier series expansion of VCD of thephase-shift controlled rectifier is expressed as

VCD = VL4

n=1,3,5...

1

nsin (n0t+ n) cos

(n2

)(5)

Fig. 3(d) shows the voltage and current waveforms of theproposed automotive WPT system with = 60 and thecircuital parameters shown in Table I. In this case, the thirdharmonic component and its odd multiples of the voltagesand currents are eliminated theoretically. To prevent the powerfactor from decreasing, the phase of VCD is synchronized withthat of IRx.

To compare the radiation noise spectrum of the proposedWPT system with that of the conventional WPT system, weassumed N1 = N2 = N and normalized (3) as follows.

~H(f) d~LN |I(f0)|

=ITx(f) + IRx(f)|I(f0)|

(6)

where I(f0) ITx(f0) + IRx(f0), and ITx(f0) and IRx(f0) arethe fundamental components of the primary and secondary coilcurrents in the conventional WPT system, respectively. Theright-hand side of (6) can be used to calculate the normalizedEMI spectrum of a WPT system without any electromagneticfield simulation. When calculating the normalized EMI spectra,the reference direction for the currents should be consideredcarefully.

Fig. 4 shows the normalized EMI spectra of the conven-tional WPT system shown in Fig. 2 and of the proposed WPTsystem shown in Fig. 3. It should be noted that, by utilizing theproposed SHE method, the magnitudes of the third harmoniccomponent and its odd multiples are significantly reduced upto 29.8 dB, while the magnitude of the fundamental componentis almost the same as that of the conventional WPT system.

IV. CONCLUSION

This paper presents a novel SHE method of the radiationnoise from an automotive WPT system. We showed the gate-control signals of the inverter and rectifier needed for the im-plementation of the proposed SHE method, and presented the


Verification of Proposed Control Method Using Simulation :Comparison of EMI Spectra ( = /3 = 60)Verification of Proposed Control Method Using Simulation :Comparison of EMI Spectra ( = /3 = 60)

Frequency (Hz)

Mag

nitu

de (d

B)

10k 100k 1M 2M

3rd harmonics

9th 15th21st 27

th = 540 kHz

Normalized EMI Spectra

- It is verified by simulation that the certain harmonics can be reduced significantly(eliminated theoretically) by using the proposed control method.

-120

-100

-80

-60

-40

-20

0

10Conventional WPT SystemProposed WPT System

20 kHz

- 29.8 dB

Fig. 4. Comparison of the normalized peak EMI spectra from the conventionalWPT system and the proposed WPT system; The resolution bandwidths ofthe spectra are 200 Hz up to 150 kHz and 9 kHz from 150 kHz to 2 MHz.The magnitudes of the third harmonic component and its odd multiples aresignificantly reduced up to 29.8 dB.

simulation results of the voltage, current, and the normalizedEMI spectrum for the case of = 60. The simulation resultsof the normalized EMI spectrum show that the significantreduction up to 29.8 dB in the harmonic components can beachieved using the proposed SHE method.

ACKNOWLEDGMENT

The authors would like to acknowledge the technicalsupport from ANSYS Korea (ANSYS, Inc.). This work wassupported by the National Research Foundation of Korea(NRF) grant funded by the Korea government (MSIP) (No.2010-0028680).

REFERENCES[1] R. W. Carlson and B. Normann, Test results of the PLUGLESSTM

inductive charging system from Evatran Group, Inc. SAE InternationalJournal of Alternative Powertrains, vol. 3, no. 1, pp. 6471, Apr. 2014.

[2] G. Ombach, D. Kurschner, S. Mathar, and W. Chlebosz, Optimummagnetic solution for interoperable system for stationary wireless EVcharging, in Ecological Vehicles and Renewable Energies (EVER), 2015Tenth International Conference on. IEEE, 2015, pp. 18.

[3] J. M. Miller, O. C. Onar, and M. Chinthavali, Primary-side power flowcontrol of wireless power transfer for electric vehicle charging, IEEETrans. Emerg. Sel. Topics Power Electron., vol. 3, no. 1, pp. 147162,March 2015.

[4] H. Kim, C. Song, D.-H. Kim, D. H. Jung, I.-M. Kim, Y.-I. Kim, J. Kim,S. Ahn, and J. Kim, Coil design and measurements of automotivemagnetic resonant wireless charging system for high-efficiency and lowmagnetic field leakage, IEEE Trans. Microw. Theory Tech., vol. 64,no. 2, pp. 118, Jan. 2016.

[5] J. Balcells, A. Santolaria, A. Orlandi, D. Gonzalez, and J. Gago, EMIreduction in switched power converters using frequency modulationtechniques, IEEE Trans. Electromagn. Compat., vol. 47, no. 3, pp. 569576, Aug 2005.

[6] H. Kim, J. Kim, S. Jeong, S. Lee, Y. Cho, D. H. Kim, and J. Kim,EMI reduction in wireless power transfer system using spread spectrumfrequency dithering, in 2016 IEEE Wireless Power Transfer Conference(WPTC), May 2016, pp. 13.

[7] J. A. Weldon, R. S. Narayanaswami, J. C. Rudell, L. Lin, M. Otsuka,S. Dedieu, L. Tee, K.-C. Tsai, C.-W. Lee, and P. R. Gray, A 1.75-GHz highly integrated narrow-band CMOS transmitter with harmonic-rejection mixers, IEEE J. Solid-State Circuits, vol. 36, no. 12, pp. 20032015, Dec 2001.

[8] M. H. Rashid, Power Electronics: Circuits, Devices, and Applications(International Edition), 3rd ed. Upper Saddle River, New Jersey:Pearson Education, Inc., 2004, pp. 258260.

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