*2.1. Dynamic Inductive Charging*

Dynamic inductive charging means that the vehicle is charged wirelessly while in motion. For the wireless power transfer, primary coils are installed below the surface at selected elements of the airport apron road system (see Figure 1). Such a so-called ITU is supplied with an alternating current of the desired frequency by the PSU, which in turn needs a connection to the power grid. The PSU uses power electronics to modify the frequency. SAEJ2954 defines the frequency for wireless power transfer for electric vehicles in the range of 81.39–90 kHz (SAE International [9]). The electromagnetic field is created locally below the pickup unit of the moving vehicle, say, a passenger bus. Via the secondary coils within the vehicle's pickup unit, an alternating current is induced by the electromagnetic field. This alternating current is rectified and used to charge the vehicle's battery and, eventually, power its electric engine. For further technical details on the technology of dynamic inductive charging and example projects, we refer to Li and Mi [10], Cirimele et al. [11], Lukic and Pantic [12], Panchal et al. [6], Ahmad et al. [13] and Covic and Boys [14].

**Figure 1.** Components of the dynamic inductive charging system (Source: Broihan et al. [8]).

The efficiency of the system is strongly dependent on the gap between the primary and secondary coil (Imura and Hori [15] and Moon et al. [16]). The smaller the gap between the primary and secondary coils, the higher the power transmission efficiency. For this reason, dynamic inductive charging systems are suitable for flat surfaces on which low-profiled vehicles operate. This is exactly the situation on airport aprons and one of the reasons why this charging technology might be interesting for airport aprons.
