General Model and Analysis of Misalignment Characteristics of Fixed-Frequency WPT Systems

To obtain a smooth output of a wireless power transfer (WPT) system over a large-misalignment range, many efforts have been devoted to altering compensating parameters of conventional compensating topologies, such as series-series, LCC-LCC, and proposing new compensating topologies, which naturally have better misalignment performance, such as CCC and X-type. This article shows that these systems, with fixed operating frequencies and optimized misalignment performance, can be described with the same mathematical model. The model is first introduced. Then, based on this model, a general analysis on the misalignment performance of two- and multicoil WPT systems is provided. According to the output-misalignment characteristics, these systems are divided into two groups, i.e., low degree and high degree. A detailed analysis of the low-degree WPT system is performed, with either a resistive load or a battery load. It is found that most (if not all) of the reported large-misalignment WPT systems are low-degree systems and they have a similar misalignment performance. Moreover, a general design method of the compensating networks is presented for lower degree WPT systems to achieve the desired misalignment performance. As an example, the compensating networks of a two-coil WPT system are designed and the experimental results verify the proposed model and the design method.