Evaluation of Magnetic Pad Sizes and Topologies for Electric Vehicle Charging

Inductive power transfer is becoming increasingly popular in stationary electric vehicle charging systems due to improved designs. However, such optimizations are normally performed for matched topologies which are similarly sized, over constant air gaps and without significant misalignment. In a real situation where the primary and secondary pads may not be matched and may be misaligned, pad designs must take into consideration coupling factors, leakage fluxes, pad quality factors, reflected impedance, and size. This paper analyzes the effects which variations in pad sizes, topologies, and displacements in three dimensions has on these parameters. It was found that solenoid pads should not be used as a primary pad due to high leakage fluxes, low native quality factors, and the fact that they are not fully interoperable over the whole desired range of use. Bipolar pad primaries are able to couple to any secondary pad over the entire range of use required and tend to have high native quality factors. Nonpolarized pads tend to have the lowest leakage fluxes but also low coupling. Suggestions on techniques to optimize these pads have also been included.