Wireless Electric Vehicle Charger With Electromagnetic Coil-Based Position Correction Using Impedance and Resonant Frequency Detection

Wireless power transfer (WPT) is an enabling technology for electric vehicles (EV), as it eliminates driver intervention during charging. Major challenges to the adoption of WPT systems include coil misalignment and large air-gap WPT, both of which degrade the transfer efficiency. To address these issues, this article presents a compact WPT charger for the rear of an EV, capable of correcting lateral misalignment Δx using two integrated electromagnetic coils. The air-gap Δy is reduced due to the rear placement of the charging pads. The variation in Δy, however, increases due to vehicle parking accuracy, which impacts the operation of the electromagnetic coils. This article proposes a closed-loop three-stage position-correcting control algorithm capable of detecting the impedance and resonant frequency of the system, which, in conjunction with the electromagnetic coils, results in improved vehicle alignment. The experimental prototype achieves a peak dc-dc efficiency of 90.1% at 5 kW WPT. With Δy = 50 mm, the electromagnetic coils laterally align the pads within 1.75 s and correct Δx as large as 240 mm. The position-correcting control was successfully demonstrated in four parking scenarios with the charging pads being corrected to within a 10-mm radius of perfect alignment.