# Impact of Coil Misalignment in Data Transmission over the Inductive Link of an EV Wireless Charger
## 1 Introduction
In contrast to other wireless communication schemes, the inductive link involved in ICPT technology is based on near-field transmissions. Moreover, it is specially designed to maximise the efficiency of power transfer on specific conditions, such as the coil positions and their relative distances [12]. This design goal differs from the one employed in traditional wireless communication systems, which aim to maximise the power transfer with an efficiency equal to 50%. The conditions assumed in the design process do not always hold during the operation of the wireless chargers. In fact, it is expected that there will be an increased number of scenarios where coil misalignments will be present. This is due to the promotion of the use of wireless charge while the vehicle is moving (dynamic charge) or temporally stopped due to traffic signals (stationary charge) [13]. The effect of coil misalignment has already been studied in regard to power transfer, but the analysis regarding its impact on the communication channel is still missing [14]. This paper analyses the capacity of the wireless channel created between the two power coils. In particular, it is based on the scheme proposed in [10] where both data and power signals are transmitted at the same frequency in order to avoid filters, high-frequency communication modules and extra coils to couple the data to the power circuits. Specifically, it studies how this parameter, which represents an upper bond for the data bit rate, is affected by usual coil misalignments (vertical and/or horizontal). The study is carried out for different compensation topologies in order to derive conclusions about the impact of the compensation networks' selections for wireless data transfer. Some previous works have addressed the capacity of an inductive link [15; 16]. However, in these works the coils were intended for low power applications, so the systems have characteristics that cannot be applied to EV wireless chargers. Firstly, they assume that both coils share the same topology (number of turns and dimensions). In an EV, the coil in the pavement is usually bigger than the one in the car in order to improve the coil misalignment behavior [2]. In addition, they work under the assumption that the coupling between the coils is so weak that the primary current is not affected by the impedance reflected from the secondary side. As shown in [17], this assumption is not valid for EV wireless chargers. Moreover, low power applications relay on a Series-Series compensation network, but other matching topologies can be found in EV wireless chargers [18; 19]. Thus, in contrast to [15; 16] this paper extends the study of the capacity offered by an inductive link with the following main contributions:  
1. The coils are realistic for EV applications in terms of their dimensions and size. 2. Four types of compensation networks are considered, as Series-Series is not the only option considered in EV wireless chargers. 3. The reflected impedance is not neglected when deriving the electrical magnitudes affecting the computation of the channel capacity. 4. The vertical, horizontal and joint vertical and horizontal types of misalignments are analysed. This study is based on a theoretical approach for each of the four single-resonant compensation networks. The theoretical models have been compared with simulation results, which show good agreement. For all the types of tested misalignments, the Series-Series compensation network was revealed to be the topology with the lowest stability in terms of variations of its channel capacity. In contrast, the asymmetrical topologies (series-parallel and parallel-series) were the compensation networks demonstrating better tolerance to coil misalignment from the communication point of view. The rest of the paper is organised as follows: Section 2 overviews the structure of wireless chargers for electric vehicles.