**4.3 Experimental set-up**

In this case, we will focus on the WPT 1 category with an output of 3.7 kW. The experimental workplace consists of a programmable power supply, electronic load, precision power analyzer, oscilloscope, input inverter, output rectifier, additional resistors and the compensated LC circuit WPT itself. The measuring workplace is connected according to the functional diagram, see **Figure 24**. The determining factor in the selection of power components was the ability to work with a switching frequency from 200 kHz upwards. For this reason, a solution based entirely on SiC elements was chosen. The inverter is built on 1200 V JFET modules FF45R12J1W1\_B11 (Infineon) with a type current of 45 A. Due to the low values of switching times of these modules, which are actually in the order of tens of nanoseconds, it is possible to minimize the effect of inverter dead times. The rectifier is based on a 1200 V diode SiC module APTDC20H1201G (Microsemi) with a type current of 20 A.

**Figure 24.** *Block diagram of the laboratory experimental set-up.*

Here the distribution transformer is presented as the grid source, followed by active rectifier, which is responsible for regulation of PF and THDi. Then full bridge

The secondary side of the system shown in **Figure 21** is drawn in more detail in **Figure 22**. The secondary side coupling system is followed by full-bridge diode rectifier with filtering capacitor CS. Then the dc/dc step-down converter (SD) providing required charging algorithm (mostly CC&CV) is supplying the on-board

Previously described concepts are representing the mostly used configurations of power electronic systems required for the design of the wireless power chargers

The most important parameter in the design of coupling coils is undoubtedly the product of quality factors *Q* and coupling *k*. Its operating size is strongly dependent on various parameters (e.g. circuit topology, load size, coil distance, etc.) and therefore cannot be optimized directly. One option is to maximize the quality factor. To achieve maximum inductance, we make the coil as planar with square turns (**Figure 23**). In addition, due to the limitation of parasitic capacitance (we now neglect), we keep constant spacings between individual turns of size *δ<sup>v</sup>* = 4 mm. Geometric dimensions allow to wind about 26 turns. In addition, if we know the

inverter is used as VSI and supplies primary side coupling section.

*Recommended system configuration of secondary side for high power application.*

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

suited for industrial and/or automotive applications.

*Proposed coupling coil (left) and its magnetic field (right).*

battery pack.

**64**

**Figure 23.**

**Figure 22.**

**4.2 Coupling elements design**

### *4.3.1 Measurement of the operational characteristics of series: series compensated system*

On the primary side, a total of three quantities are measured with an oscilloscope. Probe "a" (THDP 0200) measures the output voltage of the inverter, probe "b" (current probe TCP 404 XL and amplifier TCPA 400) measures the primary current and probe "c" (P6015A) senses the voltage on the compensation capacitor. The secondary side is not measured by the oscilloscope at all in this configuration. Also, no resistors are connected here, and the system works directly into the ZS 7080. The applied oscilloscopic measurements on the primary side are rather indicative and do not serve to calculate the efficiency [35–37].

**Figure 25** shows an oscillograph at a load power of 2678 W. The purple waveform represents the inverter output voltage, the light blue waveform the primary current waveform, and the blue waveform represents the voltage on the primary compensation capacitor (scale 1: 1000). The real elements (influenced by parasitics) of the WPT system are the main reason why the phase shift of voltage and current is non-zero (according to theoretical assumptions it should be close to zero).

A comparison of power (**Figure 26**) and efficiency (**Figure 27**) shows that the analytical models accurately describe the behavior of the system in a wide range of frequencies and loads.

### **4.4 Electromagnetic shielding application**

Although the current system achieves very high efficiency even over long working distances, it is unsatisfactory due to hygienic limits and standards for EV charging. The main weaknesses are mainly the high switching frequency and the large intensities of the EM field. The magnetic field in the vicinity of both (optimally coupled) coils at a transmitted power of approx. 4000 W is plotted in **Figure 28**. The distribution of the field changes over time, and therefore each time point must be evaluated separately.

The picture shows a large scattering of the field into the surroundings, which must be avoided. Exact induction values at a specific distance from the center of the

coils can be obtained by introducing a spherical surface to which the EM field results are mapped. The radius of this area must be defined regarding the dimensions of the vehicle and the location of the coupling coils on its chassis. The key is especially the space in which exposed persons can normally occur. For practical reasons, therefore, it does not make sense to monitor the magnetic induction near both coils. For the sake of clarity, we state here (see **Figure 28**) the magnitude of

*Output power characteristic in dependency on load and operation frequency for measurement (left) and*

*Theoretical and Practical Design Approach of Wireless Power Systems*

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

*Efficiency characteristic in dependency on load and operation frequency for measurement (left) and simulation*

**Figure 27.**

**Figure 26.**

*simulation (right).*

**Figure 28.**

**67**

*Magnetic induction around system of unshielded coils.*

*(right).*

**Figure 25.** *Time waveforms of the primary side of tested WPT system during full load operation.*

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

**Figure 26.**

*4.3.1 Measurement of the operational characteristics of series: series compensated system*

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

On the primary side, a total of three quantities are measured with an oscilloscope. Probe "a" (THDP 0200) measures the output voltage of the inverter, probe "b" (current probe TCP 404 XL and amplifier TCPA 400) measures the primary current and probe "c" (P6015A) senses the voltage on the compensation capacitor. The secondary side is not measured by the oscilloscope at all in this configuration. Also, no resistors are connected here, and the system works directly into the ZS 7080. The applied oscilloscopic measurements on the primary side are rather

**Figure 25** shows an oscillograph at a load power of 2678 W. The purple waveform represents the inverter output voltage, the light blue waveform the primary current waveform, and the blue waveform represents the voltage on the primary compensation capacitor (scale 1: 1000). The real elements (influenced by parasitics) of the WPT system are the main reason why the phase shift of voltage and current is non-zero (according to theoretical assumptions it should be close to zero). A comparison of power (**Figure 26**) and efficiency (**Figure 27**) shows that the analytical models accurately describe the behavior of the system in a wide range of

Although the current system achieves very high efficiency even over long working distances, it is unsatisfactory due to hygienic limits and standards for EV charging. The main weaknesses are mainly the high switching frequency and the large intensities of the EM field. The magnetic field in the vicinity of both (optimally coupled) coils at a transmitted power of approx. 4000 W is plotted in **Figure 28**. The distribution of the field changes over time, and therefore each time

The picture shows a large scattering of the field into the surroundings, which must be avoided. Exact induction values at a specific distance from the center of the

*Time waveforms of the primary side of tested WPT system during full load operation.*

indicative and do not serve to calculate the efficiency [35–37].

frequencies and loads.

**Figure 25.**

**66**

**4.4 Electromagnetic shielding application**

point must be evaluated separately.

*Output power characteristic in dependency on load and operation frequency for measurement (left) and simulation (right).*

*Efficiency characteristic in dependency on load and operation frequency for measurement (left) and simulation (right).*

coils can be obtained by introducing a spherical surface to which the EM field results are mapped. The radius of this area must be defined regarding the dimensions of the vehicle and the location of the coupling coils on its chassis. The key is especially the space in which exposed persons can normally occur. For practical reasons, therefore, it does not make sense to monitor the magnetic induction near both coils. For the sake of clarity, we state here (see **Figure 28**) the magnitude of

**Figure 28.** *Magnetic induction around system of unshielded coils.*

induction on the sphere surface with a radius of 450 mm at the time (*j* = 0°), when the current passes through only one coil.

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 ferrite cores.

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

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 meeting the hygienic limits many times over.
