# Impact of Coil Misalignment in Data Transmission over the Inductive Link of an EV Wireless Charger
## 4 Analysis of the Results
\begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & **Value** \\ \hline Output & 3.7 kW @ 300 V \\ f [kHz] & 85 \\ N\({}_{1}\) [number of turns in the primary coil] & 11 \\ N\({}_{2}\) [number of turns in the secondary coil] & 14 \\ _a1_\(\times\)_b_1 [m\({}^{2}\)] & 0.75 \(\times\) 0.75 \\ _a2_\(\times\)_b_2 [m\({}^{2}\)] & 0.5 \(\times\) 0.5 \\ _gd_1 [m] & 0.2 \\ \(L\)1 [\(\mu\)H] & 240.5 \\ \(L\)2 [\(\mu\)H] & 230.6 \\ \(R\)1 [m\(\Omega\)] & 196 \\ \(R\)2 [m\(\Omega\)] & 143 \\ _R_b [\(\Omega\)] & 30 \\ C\({}_{2}\) [nF] & 15.20 \\ _C\({}_{1}\)_[nF] @ SS_ & 14.57 \\ _C\({}_{1}\)_[nF] @ SP_ & 15.02 \\ _C\({}_{1}\)_[nF] @ PS_ & 15.02 \\ _C\({}_{1}\)_[nF] @ PP_ & 14.36 \\ M [\(\mu\)H] @ _gap_ = 15 cm, _xm_ = 0 cm & 49.78 \\ M [\(\mu\)H] @ _gap_ = 20 cm, _xm_ = 0 cm & 40.8 \\ M [\(\mu\)H] @ _gap_ = 25 cm, _xm_ = 0 cm & 33.38 \\ M [\(\mu\)H] @ _xm_ = 5 cm, _gap_ = _gd_ & 40.39 \\ M [\(\mu\)H] @ _xm_ = 10 cm, _gap_ = _gd_ & 39.07 \\ M [\(\mu\)H] @ _xm_ = 15 cm, _gap_ = _gd_ & 36.72 \\ M [\(\mu\)H] @ _xm_ = 5 cm, _gap_ = 10 cm & 59.9 \\ M [\(\mu\)H] @ _xm_ = 10 cm, _gap_ = 20 cm & 39.07 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Characteristics of the EV wireless charger. Figure 4: Variations in the wireless channel capacity due to vertical misalignments. SS, Series–Series; SP, Series–Parallel; PP, Parallel–Parallel; PS, Parallel–Series; PSIM (Power Simulation Technology). When a misalignment occurs, the separation between the coils is not the one assumed in the design process. This will affect the flux concatenated by both coils, which can be measured by \(M\). As a consequence, \(f_{P_{L}}^{comp}(M)\) and \(f_{B}^{comp}(M)\) and the corresponding channel capacity will change. Observing the results, the first important conclusion is that the PP topology offers the highest communication capacity. This is due to the fact that this topology is the only one that is not working at the maximum power transfer. In the other three compensation topologies, at the operational frequency there is a peak in the power transfer to the load. Consequently, they are affected by the Q-factor imposed by the circuit. This reduces the bandwidth of the circuits and, in turn, the capacity of the wireless channel. In contrast, the PP compensation topology, even when designed according to [22], does not lead to a peak in the delivered power at 85 kHz. Thus, the diminution of the power delivered to the load is less severe if we compare it with the other ones. However, the power delivered to the load is significantly lower than in the other topologies. Figure 5: Variations in the wireless channel capacity due to horizontal misalignments. Figure 6: Variations in the wireless channel capacity due to vertical and horizontal misalignments. The difference in the positions of the maximum frequencies at which the power delivered to the load is maximum is explained by the fact that the design goal in EV wireless chargers is to maximise the efficiency [24] and not the power transfer (as communication systems do). On the other hand, the results demonstrate that the capacity of the wireless channel strongly varies with different relative positions between the coils for the Series-Series and the Parallel-Parallel compensation topologies. Specifically, for vertical misalignments, an increment in the gap of 5 cm leads to a 50% reduction in the capacity of the SS topology. This change implies nearly a 10% reduction in the channel capacity for the PP compensation network. Conversely, the variations in capacity due to vertical misalignments are much less severe for the Series-Parallel and Parallel-Series topologies. The communication capacity is less sensitive to horizontal misalignments. In Figure 5, it can be observed that the effects are practically unnoticeable when the misalignment parameter, \(xm\), is less than 30 cm.