MR Sensor-Based Coil Alignment Sensing System for Wirelessly Charged EVs

Reduced power transfer efficiency due to coil misalignment is one of the key challenges faced in the design of electric vehicle (EV) wireless charging system. For improved efficiency, perfect alignment between the primary coil (charging pad) and secondary coil (vehicle pad) is crucial. This paper proposes a new EV alignment scheme using three giant magnetoresistance (GMR) sensors placed in an equilateral triangle fashion symmetrically around the center of the spiral shaped primary coil. The primary coil with a capacitor in series is excited (at a much reduced current compared to its rated value) at its resonance frequency of 41 kHz. The magnetic field of the primary coil induces a current in the mutually coupled secondary coil. The magnetic field generated by the secondary coil modulates the magnetic field distribution of the primary which is sensed by the GMR sensors. An algorithm is designed to decide the direction and magnitude of displacement of the vehicle required for coil alignment. The GMR sensors give identical output only in the case when the two coils are perfectly aligned. A prototype of the proposed scheme was built and tested to verify its functionality. The results show that the driver can align the vehicle correctly based on the misalignment factors displayed by the algorithm, based on the GMR sensors outputs. The new system is very sensitive and does not require any changes in the charging system in the vehicle.