Three-dimensional geometric optimization of WPT coils for coupling coefficient maximization

High-power transfer capacity is a major design objective of wireless power transfer (WPT) systems. For magnetic coupling-based WPT systems, increasing the coupling coefficient of power transceiver coils is the key to improving the power transfer capacity under specified limits on resonant current and voltage stresses. An effective method to increase the coupling coefficient is to optimize the geometric distributions of the coil wire loops. The obstacle of the optimization is the high computational complexity caused by the high geometric degrees of freedom, especially for multiturn coils. This paper proposes a 3D optimization method to reduce the computational complexity and give the optimal wire loop distributions for the maximum coupling coefficient. Design examples show that the optimal wire loop distribution is nonuniform. The smallest loop-to-loop spacing occurs near the front outer circumferences of the coils. Compared with common spiral and helix coils, the optimization can achieve 20% increase in coupling coefficient. The increase in coupling coefficient and power transfer capacity is verified through experiments.