*Theoretical and Practical Design Approach of Wireless Power Systems DOI: http://dx.doi.org/10.5772/intechopen.95749*

**Figure 30.** *Magnetic induction around shielded system.*

induction on the sphere surface with a radius of 450 mm at the time (*j* = 0°), when

*Wireless Power Transfer – Recent Development, Applications and New Perspectives*

Shielding can be realized by a matrix arrangement of ferrite cores lying on the back sides of both coils. The resulting magnetic field is directed into the main coupling space, while the interior of the vehicle remains protected. The material of the cores must correspond to the operating frequency and especially to the saturation at full load. Material N87 with relative permeability >1450 and operating frequency up to 500 kHz was selected for prototype. The size of the cores is 20x30x3 mm. Due to the high price and weight of the ferrite shield, it is reasonable to lighten its resulting pattern (not to occupy the full area of the coils). The finite element method will be used for this enabling to determine the intrinsic and mutual inductances of coupling coils, ferrite saturation and losses for any arrangement of

Shielding consists of two functional elements (steps). The first is a ferrite array (plate) that holds the maximum amount of coupled flux and directs it for better bonding to the second coil. The second degree of shielding is an aluminum plate offset over a ferrite field. In the case of supersaturation of the ferrite core, this creates eddy currents that keep the field in the active space of both coils. The situation is indicated in **Figure 29** (left), the ferrite barrier (core) is drawn in gray.

From **Figure 30** we can see the beneficial effect of shielding even better. Ferrite shielding almost completely shields the field above and below the coils. In this area, the hygienic limits are fully met and without the need for additional shielding. The magnetic field of the coupling coils (**Figure 30** on the right) is now much better concentrated in the coupling space, which increases the probability of meet-

In order to verify the theoretical assumptions, an experimental prototype of a previously designed shielding was created. The photograph of the experimental

The aim was to significantly reduce the switching frequency of the supply voltage and to suppress the emission of the EM field to meet the hygienic limits according to "ICNIRP 2010" [38, 39]. The operating parameters of the newly implemented prototype are quantified in **Table 4**. The values are valid for a work-

The aluminum shield is then shown by a solid plate near the ferrite core.

the current passes through only one coil.

ing the hygienic limits many times over.

workplace is evident from **Figure 31**.

ing distance of 20 cm.

**Figure 29.**

**68**

*4.4.1 Experimental analysis of the impact of shielding system*

*Proposed electromagnetic shielding (left) and EM field distribution (right).*

ferrite cores.

**Figure 31.** *Laboratory set-up for evaluation of the EM shielding impact.*


#### **Table 4.**

*Operational parameters of the system after application of the shielding.*

Full-scale maps measured at reduced power (maximum efficiency) can be seen in **Figure 32**. The resonance is around 121 kHz, with the high efficiency range more than 10 kHz wide.

The results confirm the ability of the systems to deliver 4 kW to the load at an efficiency of>95%, which, apart from the higher supply frequency, places it in the

For medium or high-power wireless chargers, we have recommended to compose the system of input inductance, the active rectifier and the voltage source inverter, which can provide low THDi, excellent power factor and controllable

The experimental prototype has proven the validity of presented physical principles and confirmed the proposed conceptual design strategies. It has also shown and discussed the comparison between ac-ac and dc-dc system efficiency relating to

Additionally, the measurement of leakage magnetic field has shown the real flux density distribution observed around the circular-shaped coupling coils. This could

This research was supported by project funding APVV – 17 – 0345 - Research of

\*, Jakub Skorvaga<sup>2</sup> and Martin Zavrel<sup>1</sup>

the optimization procedures for improvement of transfer, safety and reliability characteristics of WET systems. This research was also funded by the Ministry of Education, Youth and Sports of the Czech Republic under the project OP VVV Electrical Engineering Technologies with High-Level of Embedded Intelligence CZ.02.1.01/0.0/0.0/18\_069/0009855 and by funding program of the University of

output voltage. Thus, no additional dc/dc converters are needed.

*Theoretical and Practical Design Approach of Wireless Power Systems*

*DOI: http://dx.doi.org/10.5772/intechopen.95749*

losses-to-power transfer ratio.

be used for further optimization.

West Bohemia number SGS-2018-009.

The authors declare no conflict of interest.

, Michal Frivaldsky<sup>2</sup>

provided the original work is properly cited.

1 Faculty of Electrical Engineering, University of West Bohemia, Pilsen,

\*Address all correspondence to: michal.frivaldsky@feit.uniza.sk

2 Faculty of Electrical Engineering and Information Technologies, University of

© 2021 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

**Acknowledgements**

**Conflict of interest**

**Author details**

Vladimir Kindl<sup>1</sup>

Czech Republic

**71**

Zilina, Zilina, Slovakia

**Figure 32.**

*Output power characteristic (left) and efficiency characteristic (right) for shielded system and 20 cm power transfer distance.*

#### **Figure 33.**

*Evaluation of the values of magnetic field around shielded (system) and non-shielded system (right) during experimental measurement at full power of proposed system.*

"WPT 1" category according to the "SAE TIR J2954" wireless charging station standard.

To verify the shielding efficiency, a scattering magnetic field was also measured (measurement uncertainty <2%) around the coupling coils using a calibrated Narda ELT 400 probe. The values were recorded in the cutting plane with a regular step of 10 cm in length (**Figure 33**). The values of the magnetic induction relevant for hygienic limits are boarded by red dashed line (**Figure 33** left). It is seen, that specified limits are achieved approximately 20 cm from the top surface of the coils. Compared to unshielded system (**Figure 33** right), it is reduction of approximately 60 cm considering the spherical distance.

Based on the received and verified results it was achieved, that with the use of presented methodology, it is possible to design wireless charger, whose characteristics will meet standards and normative defined by regulatory companies.

## **5. Conclusions**

The paper has given a brief recapitulation of most important standards and regulations relating to the high-power wireless charging systems. It has proposed the magnetic couplers to be designed exactly according to optimal operation to the specific load.

*Theoretical and Practical Design Approach of Wireless Power Systems DOI: http://dx.doi.org/10.5772/intechopen.95749*

For medium or high-power wireless chargers, we have recommended to compose the system of input inductance, the active rectifier and the voltage source inverter, which can provide low THDi, excellent power factor and controllable output voltage. Thus, no additional dc/dc converters are needed.

The experimental prototype has proven the validity of presented physical principles and confirmed the proposed conceptual design strategies. It has also shown and discussed the comparison between ac-ac and dc-dc system efficiency relating to losses-to-power transfer ratio.

Additionally, the measurement of leakage magnetic field has shown the real flux density distribution observed around the circular-shaped coupling coils. This could be used for further optimization.
