# An Inverter Topology for Wireless Power Transfer System with Multiple Transmitter Coils
## 3 Transmitter Coil Excitation
### Transmitter Coil Pattern Selection  
Each transmitter coil in the proposed system can be excited separately or simultaneously, depending on the switching pattern of the excitation switches (S\({}_{1}\)-S\({}_{4}\)) of the proposed inverter circuit, as listed in Table 1. The values of the switching function, \"1\" and \"0\", indicate that the excitation switches are turned on and off, respectively. This results in 16 transmitter coil patterns, corresponding with the activated coil. For efficient power transfer, transmitter coils pattern with weakly coupling coefficients should not be energized. Only the tightly coupled transmitter coil pattern, which is defined as the proper transmitter coil pattern, is excited. The proper coil pattern generally gives the highest magnetic coupling available, which maximizes the transfer efficiency of the WPT system. The proposed selection of the transmitter coil pattern is based on the obtained current \(\left|\overset{\rightarrow}{I}_{PT}\right|\) from the detection operation. Initially, the current \(\left|\overset{\rightarrow}{I}_{PT}\right|\) is measured as the receiver coil is laterally moved along the +X direction, as shown in Figure 12. When the receiver coil position is changed from 3 to 4 cm, the \(\left|\overset{\rightarrow}{I}_{PT}\right|\) value obtained from transmitter coil 1 is increased from 1.5 to 2 A, which is the highest rate of change of \(\left|\overset{\rightarrow}{I}_{PT}\right|\). This  
Figure 11: Position of the receiver coil: (**a**) Close to the center of transmitter coil number 3; (**b**) Between transmitter coil numbers 3 and 4. Figure 10: Relationship of total primary current and magnetic coupling coefficient. means that the magnetic coupling between transmitter coil 1 and the receiver coil is greatly reduced at this point. The current of 1.5 A is empirically imposed as the current limit value, \(\left|\overset{-limit}{I_{PT}}\right|\), for the excitation decision of each of the transmitter coils. The proposed coil selection procedure is outlined as follows. First, each transmitter coil is excited at a time. The magnitude of the transmitter current in each coil is identical to \(\left|\overset{-limit}{I_{PT}}\right|\) in this case. Then, each measured transmitter current is compared with \(\left|\overset{-limit}{I_{PT}}\right|\). If \(\left|\overset{-limit}{I_{PT}}\right|>\left|\overset{-limit}{I_{PT}}\right|\), the excitation switch to the activated transmitter coil is set to \"0\" or turned off, because the magnetic coupling is rather weak, indicating that the receiver coil is located away from the activated transmitter coil. If \(\left|\overset{-limit}{I_{PT}}\right|\leq\left|\overset{-limit}{I_{PT}}\right|\), the receiver coil is relatively close to the excited coil, and the corresponding excitation switch will be set to \"1\" or turned on. After the comparison process, the switching pattern for a proper transmitter coil pattern is obtained. \begin{table}
\begin{tabular}{c c c c c c} \hline \multirow{2}{*}{**Switching Pattern**} & \multicolumn{4}{c}{**Switching Function**} & \multirow{2}{*}{**Activated Coil**} \\ \cline{2-2} \cline{4-5}  & **S\({}_{1}\)** & **S\({}_{2}\)** & **S\({}_{3}\)** & **S\({}_{4}\)** & \\ \hline
0 & 0 & 0 & 0 & 0 & None \\ \hline
1 & 0 & 0 & 0 & 1 & Coil No.4 \\ \hline
2 & 0 & 0 & 1 & 0 & Coil No.3 \\ \hline
3 & 0 & 0 & 1 & 1 & Coil No.3, 4 \\ \hline
4 & 0 & 1 & 0 & 0 & Coil No.2 \\ \hline
5 & 0 & 1 & 0 & 1 & Coil No.2, 4 \\ \hline
6 & 0 & 1 & 1 & 0 & Coil No.2, 3 \\ \hline
7 & 0 & 1 & 1 & 1 & Coil No.2, 3, 4 \\ \hline
8 & 1 & 0 & 0 & 0 & Coil No.1 \\ \hline
9 & 1 & 0 & 0 & 1 & Coil No.1, 4 \\ \hline
10 & 1 & 0 & 1 & 0 & Coil No.1, 3 \\ \hline
11 & 1 & 0 & 1 & 1 & Coil No.1, 3, 4 \\ \hline
12 & 1 & 1 & 0 & 0 & Coil No.1, 2 \\ \hline
13 & 1 & 1 & 0 & 1 & Coil No.1, 2, 4 \\ \hline
14 & 1 & 1 & 1 & 0 & Coil No.1, 2, 3 \\ \hline
15 & 1 & 1 & 1 & 1 & Coil No.1, 2, 3, 4 \\ \hline \end{tabular}
\end{table} 
Table 1: Possible switching patterns of the inverter circuit with n = 4.