High efficiency wireless power transmission at low frequency using permanent magnet coupling

• Main Author: Li, Weilai
• Language: English
• Published: University of British Columbia 2009
• Online Access: http://hdl.handle.net/2429/12599

A new method of electrical wireless power transfer has been parameterized and experimentally verified for a variety of size-scales and applications. The main distinction between this and previous methods of wireless power transfer is the nature of the coupling mechanism, which is a magnetic interaction between synchronized, rotating, permanent magnets. Its main components can be viewed as equivalent to an electric motor, a magnetic gear, and an electric generator. Its performance parameters such as power, range and efficiency are within the same order of magnitude as previously known resonant inductive power transfer devices. However, it has the distinct benefit of operating at much lower operating frequencies. A theoretical model of the new system has been developed with sufficient detail to characterize and predict experimental behavior of various sizes. The theoretical treatment has been divided into three main interactions: the motor, the generator and the magnetic gear. The mechanism for operation, as well as a model for efficiency and losses have been developed for each interaction. The viability of this new method of wireless power transfer was experimentally verified for two size-scales. The larger size-scale achieved 1.6 kW of power transfer with 15 cm separation. The main target applications of this size-scale are for wireless charging of electric vehicles and industrial applications. The smaller size-scale achieved 60 W of power transfer with 10 cm separation. The main target applications of this size-scale are for powering medical implants and consumer electronics. Both size-scales achieved efficiencies in the range of 81%, and the operating frequency did not exceed 150 Hz. The design and construction of the devices are outlined for both size-scales. Misalignment tolerance between the transmitting device and the receiver device was experimentally investigated, and related control schemes for managing the power transfer were implemented and tested. Additionally, the potential risk to human health from the time-varying magnetic field produced by this system was evaluated using exposure limits set within two widely adopted standards. For short-term exposure to the larger-scale device, the fields met the standards at a distance beyond 6 cm, and for long-term exposure, beyond 1 meter.