Design, analysis and application of dynamic wireless power transfer

Abstract

The wireless communication technologies has been found in all aspects of our social and economic life. However, the research on the wireless power transmission (WPT) has not been well established relatively. A strong driving force for the WPT technologies comes from the consumer electronics and the commercialization of electric vehicles (EV) recently. WPT provides a simple, unified and safe means to recharge the battery. With an extensive integration of this technique, the built-in battery size can be minimized to reduce system volume and cost. After performing a comprehensive review of the near-field WPT technologies, three major issues including unstable magnetic coupling, inflexible system architecture and susceptible power transmission are identified as the obstacles in extending the WPT technique into the dynamic application. To provide a stable magnetic coupling for power transmission, the optimal design of the magnetic coupler is studied. The power transfer efficiency and power transfer capability are first modelled by combination of circuit theory and finite element analysis (FEA) to provide a basic for subsequent design. A comparative study is then conducted to evaluate most of the design considerations for magnetic couplers. An optimal design method is finally introduced. A 30×30cm single layer compound winding transmitter is proposed for charging the portable devices. The uniform magnetic coupling is targeted such that the power transmission is less sensitive to the relative position of the receiver. The system with multiple modular transmitter and receiver are proposed to provide a more flexible system structure. The interaction of the magnetic field between adjacent modular is first studied. The flux cancellation phenomenon is identified and found relative to the direction of the exciting currents. A comprehensive comparison of the system configuration is then conducted. The magnetic coupling and the power transfer capability are evaluated for two system topologies and six different configurations by FEA. Two most promising configurations are selected with either the most stable magnetic coupling or the most significant power transfer capability. To avoid the power transfer sensitivity to the magnetic coupling and load variations, a new prototype and corresponding control method are proposed. The load-independent operation modes for different compensation topologies are derived by circuit analysis. Then, one of the aforementioned modular transmitter topology is selected for stable magnetic coupling, such that the load-independent characteristics extends into the dynamic situations. As a result, the load-independent and free-positioning features are satisfied simultaneously. An experimental prototype has been built tentatively for the wireless LED lighting system. A constant output voltage is guaranteed on the receiver side when the receiver moves along the transmitter array or when the load changes. Additionally, due to the decoupled control between the primary side and the secondary side the requirement on communication is eliminated.