# Impact of Coil Misalignment in Data Transmission over the Inductive Link of an EV Wireless Charger
## 1 Introduction  
Wireless charging is now a reality and a wide range of commercial low-power products are equipped with this technology [1]. In addition to common mobile phone devices and some biomedical electronics, the commodity of use associated with wireless power transfer also makes it attractive for medium power devices (kW level). In this range, electric vehicles (EVs) are clear candidates that could benefit from the wireless power transfer, to charge their batteries in a safer and easier way. Inductively Coupled Power Transfer (ICPT) technology is the most mature mechanism applied to the wireless charge of EVs [2]. It basically consists of a pair of loosely coupled coils. The one in the pavement (referred as the primary side) is excited with a time-varying current, which induces a voltage in the secondary coil, that is, the coil placed in the EV chassis. This voltage is employed to charge the battery that is connected to the secondary coil [3]. To enhance the power transfer, reactive components (typically named compensation networks) are added to both coils. Power converters are also inserted in the chargers to ensure a high-frequency magnetic field [4]. The adequate operation of the EV wireless chargers requires some mechanisms that control the correct current and/or voltage, which are provided to the battery once permitted. Thus, the primary and the secondary side need some information exchange [5] (e.g., some billing information or some electrical status about the battery). This information does not only occur during the charge, but it can also occur with no charge. For instance, in a V2G (Vehicle-to-Grid) scenario, the vehicle and the grid need to exchange some data about prices or the battery State-Of-Charge (SOC) to decide whether it is convenient or not to perform a charge or a discharge [6]. For this information exchange, wired communication is advised against, as it will eliminate the main benefits reported by the wireless chargers. Several wireless-based communication techniques have been proposed as alternatives. The more straightforward strategy consists of opting for some commercial wireless modules, which could be inserted in the primary and secondary sides. Coordination between the modules and some security drawbacks are the main concerns which could make this solution inoperative [7]. To obtain more reliable communication, these solutions can be complemented, or even avoided, by using the same wireless link that is involved with the wireless charger. Several papers have been published regarding the use of the coils for the simultaneous transmission of data and power in EV wireless chargers. In [8], the authors designed a scheme where both data and power are transmitted at the same time. Specifically, data and power are generated at different frequencies (1.6 MHz and 22.4 kHz, respectively). A similar scheme was published in [9]. Both schemes are complex to implement, as they have to add high-frequency data communication modules, extra coils and filters to separate the power and data processing accordingly. As demonstrated in [10; 11], additional costs can be avoided if the power converters employed to create the high-frequency signal generate the data signal too. According to this strategy, data and power are transmitted at the same frequency. The work in [10] included experimental results which show how this kind of combination is feasible for a 700-W wireless charger operating at 22 kHz. In fact, the spectrum of the data signal is centered at the frequency in which the wireless charger resonates. On the other hand, the data protocol is based on the BFSK (Binary Frequency Shift Keying). As demonstrated in [10], when the data and the power are transmitted at the same frequency, a data protocol needs to then be designed. To do so, some features of the wireless link over the inductive channel need to be characterised. Among these characteristics, it is necessary to know the communication capacity of the link, which limits the bit rate that the wireless channel can support.