High efficiency resonator coils for large gap wireless power transfer systems
High efficiency resonator coils for large gap resonant wireless power transfer (WPT), and a coil design methodology are disclosed. Resonator coils comprise a coil topology defined by coil parameters in which turn dimensions, such as trace widths and spacings of each turn, are configured to reduce or minimize a variance of the z component of magnetic field, over an area of a charging plane at a specified distance, or distance range, from the coil. A Tx resonator coil comprises a capacitor arrangement of tuning and network-matching capacitors for improved coil-to-coil efficiency and end-to-end WPT system performance, e.g. for applications such as through-wall WPT, in the range of tens of watts to at least hundreds of watts. Planar resonator coil topologies are compatible with fabrication using low cost PCB technology, e.g. with multi-layer metal, to reduce losses and improve thermal performance.
1. A method of configuring a resonator coil, comprising:
obtaining a population of parameters (a 1 , b 1 , . . . a n , b n ) initial defining an initial (reference) coil topology to be optimized, the population of parameters (a 1 , b 1 , . . . a n n , b n ) initial defining comprising: a maximum coil dimension, a number of turns, a minimum spacing between turns, a minimum trace with, et al. for each turn;
obtaining a target specification, comprising:
selecting a gap distance D gap from the coil to a charging surface;
selecting a charging area Area charging of the charging surface relative to an area of the coil Area coil ;
selecting a Figure of Merit (FOM) which is derived from a vertical magnetic field distribution H z over the charging area Area charging of the charging surface at gap distance D gap from the coil;
a) for the initial population of parameters (a 1 , b 1 . . . a n , b n ), computing the vertical magnetic field distribution H z over the charging plane;
b) computing the FOM based on a fitness function F(H z ) over said area of the charging plane;
c) systematically changing the population of parameters, and for each of a plurality of m populations of parameters (a 1 , b 1 . . . a n , b n ) m where m=2 to m=M, computing H z over the charging plane and computing the fitness function F(H z ) m over the charging plane;
d) when the value of the fitness function F(H z ) for an mth population of parameters (a 1 , b 1 . . . a n , b n ) m meets a target specification, storing the mth population of parameters (a 1 , b 1 a n , b n ) m as a target population of parameters; and
e) outputting the set of parameters (a 1 , b 1 . . . a n , b n ) m corresponding to the target value of the fitness function F(H z ), to define a coil topology meeting the target specification having a coil distribution comprising said dimensions, trace widths and spacings of each of the n turns.
2. The method of claim 1 wherein the FOM is a variance of the vertical magnetic field distribution H z over a target area of a charging plane spaced a distance D gap from the plane of the plan of the coil.
3. The method of claim 2 wherein the target specification comprises minimum value of said variance.