Avoiding Null Power Point in DD coils

DD coils are one of the most used coupling arrangements for the tracks and the pickups in dynamic wireless power transfer system. They reach a higher coupling coefficient with respect to conventional coil pairs with the same dimensions and assure a more effective and efficient power transfer to the electric vehicles. On the other hand, DD coils suffer of the phenomenon known as null power point, by which the power transferred to the pickup, is zero even if it is still partially coupled to the transmitting track coil. The null power points are typically removed by installing the so-called Q coil in the pickup. The power transferred to the Q coils is added to that harvested by the DD coil by a separate power converter so that the overall architecture of the receiving side of the dynamic wireless power transfer system results rather intricate. This paper presents a different approach to the problem of the null power points, based on the switching between two different supplying modes of the track DD coils. In front of a more complex architecture of the power supply system of the track, this approach gets rid of the Q coil and of the relevant power converter. The proposed solution is at first studied analytically with an approximated model of the DD coils and then verified by means of a FEM analysis and simulation.