A Smart Primary Pad With Integrated TMR Sensors for Wirelessly Charged EVs

In this article, a simple and efficient sensing mechanism, using tunneling magnetoresistance (TMR) sensors and a measurement scheme is presented to enable the primary pad to automatically detect and identify the secondary pad in an electric vehicle (EV). In wirelessly charged EVs, a primary pad that can interoperate with different types of secondary pads is highly beneficial. A bipolar pad (BPP) primary can be configured to transfer power to a circular pad (CP) or a double-D pad (DDP) secondary. In the proposed system, during the sensing phase, the primary pad is excited at a very low current (<; 200 mA) in a non-polarized mode at the resonance frequency, 43.8 kHz, of the primary. When a CP secondary is present above the primary, the frequency bifurcation effect due to the high coupling coefficient ( k) is clearly observed. This reduces the primary current considerably. In addition, the magnitude of the primary magnetic field is modulated/changed due to the magnetic field of the secondary. When a DDP secondary is present above the primary, a slight yet repeatable change is seen in the primary magnetic field due to the modulation, while the frequency bifurcation is not seen as the k is very low. The simulation and experimental studies show that these features can be used to reliably detect and identify the type of secondary pad. In the prototype developed, TMR sensors are integrated at the optimal locations on the primary pad to sense the change in the magnetic flux density. In addition, the prototype pad and sensor system developed distinguishes between the metallic body and the secondary pad so that an accidental turning on of the primary pad can be avoided. The results, from the laboratory prototype built and tested in detail, validate the functionality and usefulness of the proposed scheme.