Lateral Position Error Reduction Using Misalignment-Sensing Coils in Inductive Power Transfer Systems

Inductive power transfer (IPT) remains one of the most common ways to achieve wireless power transmission, operating on the same electromagnetic principle as electrical transformers but with an air core instead of an iron core. IPT has been implemented in many applications, including wireless charging of consumer products like smartphones and electric vehicles. However, one challenge with using IPT is ensuring precise alignment between the primary and secondary coils of the system so that maximum power transfer can take place. In this paper, the use of misalignment-sensing coils to detect and correct lateral misalignments in an IPT system is modeled and tested. The sensing coils exploit magnetic-field symmetry to give a nonlinear measurement of misalignment direction and magnitude. Experiments using such sensing coils give a misalignment sensing resolution better than 1 mm when applied to a commercial smartphone wireless charger. Voltage readings from the sensing coils are used for closed-loop control of an experimental two-dimensional coil positioner that can reduce lateral misalignments as large as 35 mm to less than 1.4 mm, allowing for effective power transfer. A similar sensing coil concept can be used to reduce lateral misalignments in scaled IPT systems, such as electric-vehicle wireless chargers.