# An Inverter Topology for Wireless Power Transfer System with Multiple Transmitter Coils
## 5 Experimental Results  
To validate the proposed system, an experimental setup of the WPT multi-coil system is created, as shown in Figure 16. Four identical coils are used as multiple transmitter coils. Each coil is made of 32 turns of litz wire. The inner and outer diameters are 10 cm and 30 cm, respectively. The receiver coil is a two-layer spiral coil with 30 turns of litz-wire for each layer. The inner and outer diameters are 12 cm and 30 cm, respectively. The air gap between the coupled coils is maintained at 10 cm. The transmitter coil is placed in a fixed position, whereas the receiver coil can be laterally moved in a designated area. This results in the horizontal misalignment. The measured circuit parameters are listed in Table 2. The input DC voltage is set to 150 V. The switching frequency is fixed at 58.51 kHz. Experimental waveforms under normal mode operation are shown in Figure 17. The receiver coil is placed at the center or zero horizontal misalignment. Switching pattern 15 is applied, where all the transmitter coils are energized. The angle \(\alpha\) is at 58 degrees. As seen in Figure 17b, the transmitter current in each coil is almost identical in both magnitude and phase. The summation of all the transmitter coil currents are equal to the total primary current, \(I_{PT}\). From the output voltage \(V_{out}\) and current \(I_{out}\) shown in Figure 17c, the output power is obtained as 500 watts. The results of the output voltage regulation when the load resistance is abruptly changed from 123.2 to 151.2 \(\Omega\) is shown in Figure 18. The desired output voltage, \(V_{out}^{*}\), is 200 V. Without the output voltage regulation, the output voltage is rising to 240 V as the load resistance is instantaneously \begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameters** & **Symbol** & **Value** \\ \hline Self-inductance of transmitter coil & L\({}_{\text{PI}}\)–L\({}_{\text{P4}}\) & 280 uH \\ Self-inductance of receiver coil & L\({}_{\text{S}}\) & 1,370 uH \\ Winding resistance of transmitter coil & R\({}_{\text{PI}}\)–R\({}_{\text{P4}}\) & 0.33 \(\Omega\) \\ Winding resistance of receiver coil & R\({}_{\text{S}}\) & 2.03 \(\Omega\) \\ Load resistance & R\({}_{\text{L}}\) & 123.2 \(\Omega\) \\ Primary compensation capacitance & C\({}_{\text{PI}}\)–C\({}_{\text{P4}}\) & 26.4 nF \\ Secondary compensation capacitance & C\({}_{\text{S}}\) & 5.4 nF \\ Filter capacitance & C\({}_{\text{f}}\) & 560 uF \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Measured circuit parameters. Figure 16: Experimental setup: (**a**) Overall system; (**b**) Multiple transmitter coils; (**c**) Single receiver coil. increased, as seen in Figure 18a. With the proposed controller, the output voltage change is negligible and regulated at the desired value, as shown in Figure 18b. Experimental waveforms under detection mode operation are shown in Figure 19. The receiver coil is moved 10 cm from the center and placed between transmitter coils 3 and 4. Each transmitter coil is energized at a time. The angle \(\alpha\) is set to 126 degrees. The output signal from the current sensor,  
Figure 17: Experimental waveforms of the system under normal mode operation: (**a**) Gate signals of the inverter’s main switches (V\({}_{\text{GS,SU}}\) and V\({}_{\text{GS,SL}}\)), inverter voltage (V\({}_{\text{INV}}\)), and total primary current (I\({}_{\text{PT}}\)); (**b**) Current in each transmitter coil (I\({}_{\text{PT}}\)–I\({}_{\text{P4}}\)); (**c**) Secondary voltage (V\({}_{\text{S}}\)), secondary current (I\({}_{\text{S}}\)), output voltage (V\({}_{\text{out}}\)), and output current (I\({}_{\text{out}}\)). \(|I_{PT}|\), is illustrated. In Figure 19a,b, the \(|I_{PT}|\) values of transmitter coils 1 and 2 are 2.2 A and 2.1 A, respectively. These values are greater than the imposed limit \(\left|I_{PT}^{limit}\right|\) at 1.5 A. This is an indication that the receiver coil is placed far away from both transmitter coils, where the magnetic coupling is weak.