Sensor System to Aid the Vehicle Alignment for Inductive EV Chargers

For efficient power transfer in an inductive power transfer system, the primary coil, placed inside the charging pad, and the secondary coil, kept inside the vehicle pad, must be aligned correctly. Information about the real-time position of the electric vehicle (EV) with respect to the charging pad is required to aid the driver in the alignment of the two coils. This paper proposes a wireless LC-based scheme using three small sensing coils kept close to the primary coil, to detect the position of the EV. Each sensing coil has a capacitor connected to it, forming three LC tank circuits. The measurement circuit, which is connected to the secondary coil, measures the coupling coefficient between the secondary coil and each of the LC coils. Based on these values, the direction in which the EV should be driven to align the two coils is determined. This information is displayed to the driver. A prototype of the proposed scheme is designed and tested. Using the proposed scheme, the primary and the secondary coils are aligned correctly. This is verified by exciting the primary coil of the prototype by a power source at 50 kHz and measuring the induced voltage in the secondary coil, which is found to be the maximum when the two coils are aligned using the proposed scheme.