High-power magnetically coupled resonant (MCR) bidirectional wireless power transfer (BWPT) within long distance can be potentially used in various applications. However, the coupling between transmission coils will drastically decrease with the rise of distance to diameter (d-D) ratio, and voltage/current stresses on resonant components tend to increase apparently, which further deteriorate the system efficiency and stability. In this paper, the relationship between the coupling coefficient and the d-D ratio in high-power BWPT systems is analyzed by mathematics methods. The correlations of transferred power and system efficiency with d-D ratio are presented consequently. The scheme of coils magnetic concentration and double-layer coils in parallel is adopted to improve the system performance. The theoretical analysis is demonstrated by the experimental results of a 2kW prototype, and the system efficiency is improved from 70.7% to 77.47% under the d-D ratio of 1 (300mm-300mm).

Nowadays, the magnetically coupled resonant (MCR) wireless power transfer (WPT) system are mostly the single-source or single-load systems that operate at “one to one” mode. With the increasing number of electrical equipment and types of input sources, the “one to one” mode cannot meet the application requirements. Therefore, the "one-to-many" and "many-to-many" WPT become increasingly important. In this paper, a three-port MCR wireless energy router (Wi E-Router) architecture with dual sources and dual loads is investigated in detail, which allows power transfer among dual sources and dual loads wirelessly. The equivalent circuit model of the system is built to analyze its transfer characteristics. Moreover, an effective power management strategy for a variety of input power cases is proposed. Finally, the theoretical analysis is validated by the experimental results from a 600 W prototype.

Multi-module series-parallel (MMSP) power systems have the superiority of easy scalability and high reliability, and is the prospective candidate for high-power conversion. In this paper, the MMSP configuration is implemented in wireless power transfer (WPT) applications. However, the voltage and current sharing issues have not been analyzed precisely in existing researches. To obtain the inherent principle of voltage and current sharing in the MMSP WPT system, the dual-module series-parallel WPT systems with four configurations are studied as examples. By the fundamental harmonic analysis, the characteristics of a WPT module are obtained, and then the imbalance mechanism of voltage and current under four kinds of parameters mismatches are revealed. The results of circuit simulation verify the correctness of the theoretical analysis.

For multi-source and multi-load wireless power transfer (WPT) applications, a novel architecture of modular stacked multi-port wireless energy interconnection system (WEIS) with virtual AC bus is presented in this paper, which has following advantages: 1) it can serve as the interface among multiple sources and multiple loads; 2) bipolar coils are applied to eliminate the cross-coupling among multiple coils; 3) the relay coils with constant current characteristics are adopted as a virtual AC bus, and the system power distribution is greatly simplified by the proposed phase-shifted control method; 4) the modularization of power converters, coils and compensation networks greatly enhances the system applicability and scalability. A four-port WEIS prototype with the rated power of 2kW was built, and experiments were carried out for typical operation modes including single-source three-load mode and dual-source dual-load mode, which verified the effectiveness of the proposed system architecture.

Nowadays, bidirectional wireless power transfer (BWPT) technology has caused increasingly concern, but its application is greatly limited when the number of sources and loads increases. In this paper, the concept of multi-port wireless energy router (Wi E-Router) is proposed to realize energy transfer wirelessly among multiple sources and loads for the multi-source and multi-load wireless power transfer (WPT) applications. Specifically, a three-port magnetically coupling resonant (MCR) Wi E-Router with LCC hybrid compensation network is investigated in detail. The equivalent circuit model of the three-port Wi E-Router is built and the power transfer characteristics are analyzed. Based on the circuit model, the relationships between the power magnitude as well as flowing direction and the shifted phase among or inside multiple ports are revealed. Moreover, a zero-power-flow control scheme is put forward for the case when one port quits from the system. By regulating the outer shifted phase, the power transfer among other ports can still be realized when the idling port achieves zero power flow. Finally, the validity of the above theoretical analysis is verified by experiments.