Determining the Maximum Power Transfer Points for MC-WPT Systems With Arbitrary Number of Coils

To reveal the general characteristic of the maximum power transfer points of magnetic coupling wireless power transfer (MC-WPT) systems, and to quickly and accurately determine all possible maximum power transfer points for arbitrary coil MC-WPT systems, a novel theoretical analysis method is proposed in this paper. Based on the modal theory, an accurate time-domain model of an n-coil MC-WPT system is established and the analytical current response on each coil is derived. According to the current response of the load, a detailed power spectrum distribution is presented, based on which the mathematic expressions of all possible maximum power transfer points, including the maximum output powers and corresponding operating frequencies, are deduced. The theoretical results are verified in experiment prototypes practically. The experimental results show that: 1) the output power reaches its maximum value at the modal frequencies rather than the designed natural frequency of the resonators in MC-WPT systems; 2) there are n modal frequencies of an n-coil MC-WPT system. The analysis results provide useful information to choose the operating frequency for practical MC-WPT systems with arbitrary number of coils.