Coexistence of Dual Inductive Wireless Power Transfer Systems

Abstract: Wireless power transfer is emerging into everyday life. The idea is to create a more convenient way of charging, or at least powering, devices. Ideally, all power transmitters and power-receiving devices should be interoperable so that the user does not need to investigate whether a specific power transmitter will work together with a specific device. Interoperability is what the standard Qi, invented by the Wireless Power Consortium, has achieved for the wireless charging of smartphones since its release in 2008, which also leads to its phenomenal success. However, when it comes to cordless kitchen appliances, the standard (called Ki) is still under development; the idea is to transform the kitchen into a cordless environment, for the user’s convenience. Unlike Qi, which standardizes power transfer in the order of tens of watts, Ki should safely handle power level of up to the kilowatt range. Hence, Ki is technically more challenging to develop. This thesis investigates how the dual wireless power systems proposed in Ki may coexist in space and time. One system is used to transfer high power levels in the kilowatt range for appliance operation, while the other utilizes low power of less than 1 watt for communication needs. To simply implementation, the current Ki approach is to separate the operation of two systems in time, to bypass the need for coexistence. In this investigation, the dual wireless power systems were first characterized. It was found that the transmitting and receiving units will act significantly differently depending on the material that surrounds the power transmitter and receiving units. With the system characterized, methods to decouple the two systems (i.e., a filter and a shielding barrier) were studied. The decoupling of the two systems is important as the signals from one system can otherwise interfere with the correct operation of the other system, and viceversa. Although coexistence has not been achieved in this work, the progress made towards that direction is presented. Adequate shielding of the combined of a low-frequency magnetic field and a high-frequency electric field will require further efforts. In addition, the low-power communication system is very susceptible to interference due to its lower signal power compared to the noise emitted by the high-power system. Increasing the power level in the low-power system may enable coexistence.