# Impact of Coil Misalignment in Data Transmission over the Inductive Link of an EV Wireless Charger
## 2 Overview of a Wireless EV Charger  
The structure of an ICPT wireless charger for an EV is illustrated in Figure 1.  
In this scheme, the inductive link formed by the EV wireless charger is used to transfer the power (\(p(t)\)) and the data (\(d(t)\)), as done in [8; 9; 10]. The core of the charger is the pair of coils. When a time-varying current traverses the primary coil, a magnetic field is then generated, according to [PERSON]'s law. On the other hand, when this magnetic field is present in the secondary coil, a voltage is induced in this element, as expressed by [PERSON]'s law. The induced voltage depends on the strength of the magnetic field and how much of the magnetic flux traverses the secondary coil. Thus, the relative distance between the coils as well as their misalignment have an impact on the induced voltage. Figure 1: Structure of an Inductively Coupled Power Transfer (ICPT) wireless charger for electric vehicles (EV). In a lumped equivalent circuit, this phenomenon is modelled with the coupling factor (\(k\)) or the related mutual inductance (\(M\)). In order to have reasonably-sized coils, the magnetic field involved in this process is in the frequency range of 20-100 kHz [4]. This implies that the current injected to the primary coil must be in the aforementioned frequency range. The frequency conversion from the one provided by the grid (50-60 Hz) to the one required is performed by power converters, which are installed in the primary and the secondary sides. Therefore, the EV wireless charger depends on an inverter in the primary side and a rectifier in the secondary side. The topology of the inverter differs according to the power requirements [20]. The works in [10] and in [8] incorporated a data signal into the inductive link. In particular, the work in [10] incorporated one switch connected to the coil, to transmit the information. Both data and power signals were transmitted at the same frequency in order to avoid additional components, such as filters or extra coils. These elements are necessary to couple the data signal to the power one when both are generated at different frequencies. Other components of the EV wireless chargers are the compensation networks. These are reactive elements that help to ensure resonant operation when a predetermined set of conditions holds (e.g., the relative position between the coils). Although more complex compensation topologies [19; 21] exist, the single-resonant ones are the most common due to their simplicity. In these schemes, a primary capacitor (\(C_{1}\)) is installed on the primary side and a secondary capacitor (\(C_{2}\)) is also placed on the secondary side. The single-resonant compensation topologies are referred to as Series-Series (SS), Series-Parallel (SP), Parallel-Series (PS) and Parallel-Parallel (PP). The first term refers to the type of connection between the primary coil and the capacitor installed on this side. On the other hand, the second term in this nomenclature describes the connection between the secondary coil and the secondary capacitor. The values of the capacitors depend on the topology and the relative positions of the coils. In the design process, a certain distance between the coils is assumed so that a specific mutual inductance (\(Mi\)) is utilised during the computation of \(C_{1}\) and \(C_{2}\). An equivalent circuit, as shown in Figure 2, can be used to determine the correct capacitors. \(R_{1}\) and \(R_{2}\) represent the Equivalent Series Resistances (ESR) of the coils, whereas \(R_{b}\) stands for the equivalent resistance of the battery. \(V_{s}\) can be the data or the power signal. In our study, \(V_{s}\) corresponds to the information source. As previously stated, the goal of introducing the capacitors is to allow the system to operate under resonant conditions. When this condition holds, the input impedance seen by the source should have a null imaginary part.