Constant-coupling excitation for road-to-vehicle wireless power transfer

Dynamic wireless power transfer promises electric vehicles that charge while driving, but the coupling between a segmented roadway track and a vehicle pad varies strongly with position, so the delivered power collapses whenever the vehicle crosses a segment boundary. This paper treats that collapse as a geometry problem rather than a control problem. Applying the Poisson summation formula to the spatial coupling profile shows that the coupling seen by a moving pad is exactly position invariant when the segment pitch is placed at a null of the profile spatial spectrum, and that the residual ripple can be read directly off that spectrum before any circuit is built. The nulls are shown to lie at integer multiples of the reciprocal segment length and of the reciprocal pad length. A second result gives the excitation that holds the coupling constant with the least conduction loss: each energised segment should carry current in proportion to its own instantaneous coupling. A third result bounds the load, showing that the phase behaviour of the series compensated link splits whenever the product of coupling and loaded secondary quality factor exceeds unity, and that at the efficiency optimal load this product depends only on the ratio of the two coil quality factors and not on coupling at all, which yields a turns ratio design rule. A quasi static electromagnetic model coupled to a resonant circuit model, evaluated for an eleven kilowatt link at eighty five kilohertz over a one hundred and fifty millimetre gap, reduces delivered power ripple from about one hundred percent to about one percent. The proposed sensorless scheme is compared honestly against conventional current boosting, and the conditions under which each is preferable are identified.