*4.2. Experimental Verification*

In order to validate the correctness of the simulation results and the effectiveness and feasibility of the proposed dynamic shielding scheme, the circuit of the WPT system with double-coil active shielding is built in this paper. The structural framework is shown in Figure 12, and a physical diagram of the experimental setup is displayed in Figure 13. And the general specifications of measuring devices are listed in Appendix A. Two control experimental setups are used to better visualize the characteristics of this scheme. One group involves no shielding, and the other group involves double-coil active shielding but without the dynamic shielding scheme. double-coil active shielding is built in this paper. The structural framework is shown in Figure 12, and a physical diagram of the experimental setup is displayed in Figure 13. And the general specifications of measuring devices are listed in Appendix A. Two control experimental setups are used to better visualize the characteristics of this scheme. One group involves no shielding, and the other group involves double-coil active shielding but without the dynamic shielding scheme.

**Figure 12.** The structural framework of WPT system with double-coil active shielding. **Figure 12.** The structural framework of WPT system with double-coil active shielding.

Full Bridge Resonant Inverter

It mainly consists of four parts: (1) a power control module composed of DC power

supply and an inverter; (2) a power transmission module composed of three coils—a transmitting coil, half-loop shielding coils and receiving coil; (3) a dynamic shielding control module composed of a full-bridge inverter circuit, driving circuit, magnetic flux density detector, and micro-controller chip (MCU); (4) a load module composed of a rectifier circuit and load. The power supply for the WPT system is provided by a DC power supply, which, through the inverter, forms a high-frequency AC signal to the transmitting coil. The power is transmitted from the transmitting coil to the active shielding coils and

receiving coil and then finally rectified and converted to provide power for the load.

This work focuses on the dynamic shielding control module consisting of a full-

Experiments are conducted by assigning different values to the transmission dis-

tance. The transmission distance is varied between 10 mm and 200 mm, and the variation

bridge inverter circuit, driver circuit, magnetic flux density detector, and MCU (the dashed block part in the Figure 12). The magnetic flux density of EMF leakage is detected by the magnetic flux density detector, and it is output to the MCU; then, the MCU applies the dynamic shielding scheme to calculate the corresponding duty cycle and connects the required control signal to IR2103 to drive the conduction of four MOSFETs in the fullbridge inverter. Thus, the power supply *V*<sup>A</sup> of the active shielding coils is controlled to

Signal generator

Magnetic Flux Density Detector

realize the proposed dynamic shielding scheme.

Power supply

Inverter

MCU

**Figure 13.** Experimental setup.

but without the dynamic shielding scheme.

Coil

Supply Inverter Primary

**Figure 13.** Experimental setup. **Figure 13.** Experimental setup.

DC Power

It mainly consists of four parts: (1) a power control module composed of DC power supply and an inverter; (2) a power transmission module composed of three coils—a transmitting coil, half-loop shielding coils and receiving coil; (3) a dynamic shielding control module composed of a full-bridge inverter circuit, driving circuit, magnetic flux density detector, and micro-controller chip (MCU); (4) a load module composed of a rectifier circuit and load. The power supply for the WPT system is provided by a DC power sup-It mainly consists of four parts: (1) a power control module composed of DC power supply and an inverter; (2) a power transmission module composed of three coils—a transmitting coil, half-loop shielding coils and receiving coil; (3) a dynamic shielding control module composed of a full-bridge inverter circuit, driving circuit, magnetic flux density detector, and micro-controller chip (MCU); (4) a load module composed of a rectifier circuit and load. The power supply for the WPT system is provided by a DC power supply, which, through the inverter, forms a high-frequency AC signal to the transmitting coil. The power is transmitted from the transmitting coil to the active shielding coils and receiving coil and then finally rectified and converted to provide power for the load.

double-coil active shielding is built in this paper. The structural framework is shown in Figure 12, and a physical diagram of the experimental setup is displayed in Figure 13. And the general specifications of measuring devices are listed in Appendix A. Two control experimental setups are used to better visualize the characteristics of this scheme. One group involves no shielding, and the other group involves double-coil active shielding

> Voltage Source of Shielding Coil *V*A

Magnetic Flux Density Detector

**Figure 12.** The structural framework of WPT system with double-coil active shielding.

Secondary Coil Rectifier

Circuit

MCU

Drive Circuit IR2103

Full Bridge Resonant Inverter

Load

ply, which, through the inverter, forms a high-frequency AC signal to the transmitting coil. The power is transmitted from the transmitting coil to the active shielding coils and receiving coil and then finally rectified and converted to provide power for the load. This work focuses on the dynamic shielding control module consisting of a fullbridge inverter circuit, driver circuit, magnetic flux density detector, and MCU (the This work focuses on the dynamic shielding control module consisting of a full-bridge inverter circuit, driver circuit, magnetic flux density detector, and MCU (the dashed block part in the Figure 12). The magnetic flux density of EMF leakage is detected by the magnetic flux density detector, and it is output to the MCU; then, the MCU applies the dynamic shielding scheme to calculate the corresponding duty cycle and connects the required control signal to IR2103 to drive the conduction of four MOSFETs in the full-bridge inverter. Thus, the power supply *V*<sup>A</sup> of the active shielding coils is controlled to realize the proposed dynamic shielding scheme.

dashed block part in the Figure 12). The magnetic flux density of EMF leakage is detected by the magnetic flux density detector, and it is output to the MCU; then, the MCU applies the dynamic shielding scheme to calculate the corresponding duty cycle and connects the required control signal to IR2103 to drive the conduction of four MOSFETs in the full-Experiments are conducted by assigning different values to the transmission distance. The transmission distance is varied between 10 mm and 200 mm, and the variation step is set to 10 mm/step. The supply power *V*<sup>A</sup> is adjusted depending on the change in transmission distance. In the following, experimental results of this dynamic shielding scheme are analyzed.

bridge inverter. Thus, the power supply *V*<sup>A</sup> of the active shielding coils is controlled to realize the proposed dynamic shielding scheme. Experiments are conducted by assigning different values to the transmission distance. The transmission distance is varied between 10 mm and 200 mm, and the variation The curve of *V*<sup>A</sup> variation with the transmission distance is shown in Figure 14. According to the ICNIRP standard, the magnetic flux density *B* is 27 µT. With the gradual increase in transmission distance, *V*<sup>A</sup> decreases accordingly. In the range of 0–50 mm, *V*<sup>A</sup> decreases sharply with the increase in transmission distance, and the decline is very apparent. It is related to the drastic magnetic flux density change in the near field of the WPT system. Within 50–150 mm, the decrease in *V*<sup>A</sup> becomes slightly less, and within 150–200 mm, the change in *V*<sup>A</sup> tends towards a stable value, which is related to the limited transmission distance of WPT technology.

ured values.

mission distance of WPT technology.

scheme are analyzed.

mission distance of WPT technology.

scheme are analyzed.

*Energies* **2021**, *14*, x FOR PEER REVIEW 15 of 20

step is set to 10 mm/step. The supply power *V*<sup>A</sup> is adjusted depending on the change in transmission distance. In the following, experimental results of this dynamic shielding

The curve of *V*<sup>A</sup> variation with the transmission distance is shown in Figure 14. According to the ICNIRP standard, the magnetic flux density *B* is 27 μT. With the gradual increase in transmission distance, *V*<sup>A</sup> decreases accordingly. In the range of 0–50 mm, *V*<sup>A</sup> decreases sharply with the increase in transmission distance, and the decline is very apparent. It is related to the drastic magnetic flux density change in the near field of the WPT system. Within 50–150 mm, the decrease in *V*<sup>A</sup> becomes slightly less, and within 150–200 mm, the change in *V*<sup>A</sup> tends towards a stable value, which is related to the limited trans-

**Figure 14.** The *V*<sup>A</sup> variation with transmission distance. **Figure 14.** The *V*<sup>A</sup> variation with transmission distance. According to the guidance in Figure 14, *V*<sup>A</sup> is adjusted so that the magnetic flux den-

According to the guidance in Figure 14, *V*<sup>A</sup> is adjusted so that the magnetic flux density reaches below 27 μT at different transmission distances. The variation curves of magnetic flux density at different transmission distances are given in Figure 15. Blue indicates no shielding, red represents the case with double-coil active shielding but without the dynamic shielding scheme (here *V*<sup>A</sup> = 24 V and the initial transmission distance is 100 mm), and yellow represents the case with double-coil active shielding and with the dynamic According to the guidance in Figure 14, *V*<sup>A</sup> is adjusted so that the magnetic flux density reaches below 27 µT at different transmission distances. The variation curves of magnetic flux density at different transmission distances are given in Figure 15. Blue indicates no shielding, red represents the case with double-coil active shielding but without the dynamic shielding scheme (here *V*<sup>A</sup> = 24 V and the initial transmission distance is 100 mm), and yellow represents the case with double-coil active shielding and with the dynamic shielding scheme to adjust *V*A. Lines indicate calculated values, and dots indicate measured values. sity reaches below 27 μT at different transmission distances. The variation curves of magnetic flux density at different transmission distances are given in Figure 15. Blue indicates no shielding, red represents the case with double-coil active shielding but without the dynamic shielding scheme (here *V*<sup>A</sup> = 24 V and the initial transmission distance is 100 mm), and yellow represents the case with double-coil active shielding and with the dynamic shielding scheme to adjust *V*A. Lines indicate calculated values, and dots indicate meas-

step is set to 10 mm/step. The supply power *V*<sup>A</sup> is adjusted depending on the change in transmission distance. In the following, experimental results of this dynamic shielding

The curve of *V*<sup>A</sup> variation with the transmission distance is shown in Figure 14. According to the ICNIRP standard, the magnetic flux density *B* is 27 μT. With the gradual increase in transmission distance, *V*<sup>A</sup> decreases accordingly. In the range of 0–50 mm, *V*<sup>A</sup> decreases sharply with the increase in transmission distance, and the decline is very apparent. It is related to the drastic magnetic flux density change in the near field of the WPT system. Within 50–150 mm, the decrease in *V*<sup>A</sup> becomes slightly less, and within 150–200 mm, the change in *V*<sup>A</sup> tends towards a stable value, which is related to the limited trans-

200 0 25 50 75 100 125 150 175 **Figure 15.** Curves of magnetic flux density at different transmission distances. **Figure 15.** Curves of magnetic flux density at different transmission distances.

Transmission distance

**Figure 15.** Curves of magnetic flux density at different transmission distances. It can be seen from the three curves in Figure 15 that the measured and calculated values are in general agreement. Without shielding, the magnetic flux density within 10– 163 mm is higher than the safety limit of 27 μT, and only in the range of 163–200 mm is it below the safety standard. When double-coil active shielding is used without the dynamic shielding scheme, the magnetic flux density is significantly higher than 27 μT at a distance less than the initial transmission distance of 100 mm. The greater the distance, the greater It can be seen from the three curves in Figure 15 that the measured and calculated values are in general agreement. Without shielding, the magnetic flux density within 10– 163 mm is higher than the safety limit of 27 μT, and only in the range of 163–200 mm is it below the safety standard. When double-coil active shielding is used without the dynamic shielding scheme, the magnetic flux density is significantly higher than 27 μT at a distance less than the initial transmission distance of 100 mm. The greater the distance, the greater It can be seen from the three curves in Figure 15 that the measured and calculated values are in general agreement. Without shielding, the magnetic flux density within 10–163 mm is higher than the safety limit of 27 µT, and only in the range of 163–200 mm is it below the safety standard. When double-coil active shielding is used without the dynamic shielding scheme, the magnetic flux density is significantly higher than 27 µT at a distance less than the initial transmission distance of 100 mm. The greater the distance, the greater the flux density. Obviously, at reduced distances, the initial supply power *V*<sup>A</sup> is not sufficient to shield the EMF leakage of the WPT system. Moreover, at a distance greater than the initial transmission distance, the magnetic flux density becomes gradually lower than the safety limit, when no corresponding adjustment of *V*<sup>A</sup> will also result in a waste of resources. When adopting double-coil active shielding and applying the dynamic shielding scheme to adjust *VA*, the EMF leakage can be basically kept below the safety limit of 27 µT regardless of the increase in or shortening of the transmission distance. It avoids excessive power waste when the distance increases and solves the problem of excessive EMF exposure to human safety.

> A comparison of the shielding effectiveness *SE* with and without the dynamic shielding scheme for different transmission distances is shown in Figure 16. Measured and calculated values remain largely consistent. Without the dynamic shielding scheme, *SE* becomes progressively larger with increasing distance. This means that the closer one

approaches the coil, the less EMF leakage is shielded. The higher the level of EMF exposure, the greater the risk to humans. This is due to the fact that *V*<sup>A</sup> is not regulated accordingly. When the distance decreases, the magnetic flux density increases, and the original *V*<sup>A</sup> is no longer enough to shield a sufficient amount of EMF leakage. On the other hand, with the dynamic shielding scheme, *SE* increases when the transmission distance is smaller and decreases slightly when the transmission distance becomes longer. The closer to the transmitting coil, the higher the magnetic flux density of EMF leakage, when a higher shielding effectiveness *SE* is required to bring the EMF leakage level down to within the safe range. The results show that this method is consistent with the limits of EMF exposure requirements and validate the effectiveness of the dynamic shielding scheme. proaches the coil, the less EMF leakage is shielded. The higher the level of EMF exposure, the greater the risk to humans. This is due to the fact that *V*<sup>A</sup> is not regulated accordingly. When the distance decreases, the magnetic flux density increases, and the original *V*<sup>A</sup> is no longer enough to shield a sufficient amount of EMF leakage. On the other hand, with the dynamic shielding scheme, *SE* increases when the transmission distance is smaller and decreases slightly when the transmission distance becomes longer. The closer to the transmitting coil, the higher the magnetic flux density of EMF leakage, when a higher shielding effectiveness *SE* is required to bring the EMF leakage level down to within the safe range. The results show that this method is consistent with the limits of EMF exposure requirements and validate the effectiveness of the dynamic shielding scheme.

*Energies* **2021**, *14*, x FOR PEER REVIEW 16 of 20

EMF exposure to human safety.

the flux density. Obviously, at reduced distances, the initial supply power *V*<sup>A</sup> is not sufficient to shield the EMF leakage of the WPT system. Moreover, at a distance greater than the initial transmission distance, the magnetic flux density becomes gradually lower than the safety limit, when no corresponding adjustment of *V*<sup>A</sup> will also result in a waste of resources. When adopting double-coil active shielding and applying the dynamic shielding scheme to adjust *VA*, the EMF leakage can be basically kept below the safety limit of 27 μT regardless of the increase in or shortening of the transmission distance. It avoids excessive power waste when the distance increases and solves the problem of excessive

A comparison of the shielding effectiveness *SE* with and without the dynamic shield-

comes progressively larger with increasing distance. This means that the closer one ap-

**Figure 16.** *SE* for different transmission distances with and without dynamic shielding scheme. **Figure 16.** *SE* for different transmission distances with and without dynamic shielding scheme.

To further confirm the feasibility of this dynamic shielding scheme, the power transmission efficiency *η* of the WPT system is investigated. Figure 17 shows the variation curves of *η* at different transmission distances, where blue denotes no shielding and yellow denotes double-coil active shielding. It is clear that, although slightly fluctuating, the measured values match well with the calculated values. The *η* with double-coil active shielding is slightly reduced compared with that with no shielding, but the reduction is not significant and is approximately 3.1%. It is related to the introduction of the shielding system. It can be found that the addition of this double-coil active shielding structure achieves good shielding effectiveness against EMF leakage at the same time, without causing a significant sacrifice in power transmission efficiency. This means that the application of the double-coil dynamic shielding scheme can not only avoid the waste of power but To further confirm the feasibility of this dynamic shielding scheme, the power transmission efficiency *η* of the WPT system is investigated. Figure 17 shows the variation curves of *η* at different transmission distances, where blue denotes no shielding and yellow denotes double-coil active shielding. It is clear that, although slightly fluctuating, the measured values match well with the calculated values. The *η* with double-coil active shielding is slightly reduced compared with that with no shielding, but the reduction is not significant and is approximately 3.1%. It is related to the introduction of the shielding system. It can be found that the addition of this double-coil active shielding structure achieves good shielding effectiveness against EMF leakage at the same time, without causing a significant sacrifice in power transmission efficiency. This means that the application of the double-coil dynamic shielding scheme can not only avoid the waste of power but also reduce the degrading influence of the shielding device on the transmission performance of the WPT system; thus, its feasibility is verified. *Energies* **2021**, *14*, x FOR PEER REVIEW 17 of 20

also reduce the degrading influence of the shielding device on the transmission perfor-

**Figure 17.** Curves of *η* at different transmission distances. **Figure 17.** Curves of *η* at different transmission distances.

**5. Conclusions**

pared with other WPT systems.

agreed to the published version of the manuscript.

**Informed Consent Statement:** Not applicable.

**Institutional Review Board Statement:** Not applicable.

**Conflicts of Interest:** The authors declare no conflict of interest.

tances are verified.

61903272 and 61873180.

outside of the transmitting coil. The supply power of the active shielding coils installed on the ground is adjusted according to different transmission distances to achieve dynamic shielding of EMF leakage with different EVs. The WPT system with the proposed double-coil dynamic shielding scheme is modeled, simulated, experimented, and com-

Given that different transmission distances lead to different degrees of EMF leakage,

The simulation and experimental results show that the proposed double-coil dynamic shielding scheme can shield approximately 77.4% of the EMF leakage and maintain high shielding effectiveness as the transmission distance varies. Furthermore, the application of the double-coil dynamic shielding scheme essentially has no effect on the power transmission efficiency. Therefore, the adaptability, effectiveness, and feasibility of the double-coil dynamic shielding scheme for WPT systems with different transmission dis-

EVs currently available in the market have different structures, and the distances between their vehicle chassis and the ground are bound to be different. When the transmitting coil is fixed to the ground in the WPT system, EVs with different chassis heights signify different transmission distances. The proposed double-coil dynamic shielding scheme can shield the EMF leakage as the transmission distance changes, avoiding the repeated design of the shielding system. The proposed scheme is also generally applicable to other cases where the position of the transmitting coil is fixed but the distance of the receiving coil changes. Thus far, the scheme involves a large amount of analytical calculations, and it is hoped that a more concise method can be sought in future research.

**Author Contributions:** Conceptualization, Y.L. and Z.C.; methodology, Y.L.; software, Y.L.; validation, Y.L.; formal analysis, Y.L.; investigation, Y.L.; resources, Y.L.; data curation, Y.L.; writing original draft preparation, Y.L.; writing—review and editing, Y.L.; visualization, Y.L.; supervision, S.Z.; project administration, Z.C.; funding acquisition, Z.C. and S.Z. All authors have read and

**Funding:** This research was funded by National Natural Science Foundation of China, grant number
