Ranking Qi Wireless Power Transmitters by Efficiency

Abstract

The Wireless Power Consortium (WPC) Energy Star Task Force (ESTF), comprised of engineers from major cellphone and consumer electronics manufacturers, test houses, and others, developed a proposed efficiency-test protocol for the U.S. Environmental Protection Agency (EPA), intended to rank Qi wireless power transmitters on the basis of power-transfer efficiency. Key to this test protocol is the assumption that a single, optimally designed test receiver may be used to accurately assess transmitter efficiency and enable ranking. The possibility exists that phones using different power receiver designs (e.g., different “friendly metal” profiles, different electrical designs) will interact with transmitters and report different rankings for a given transmitter, thus invalidating the proposed test protocol. Experiments to prove or disprove the assumption that a single optimized receiver can be used as a proxy to fairly compare and rank the real-world power-transfer efficiency performance of Qi wireless power transmitters were conducted. As a result of these experiments, the WPC has concluded that because of receiver–transmitter interaction, it is not possible to rank transmitters by efficiency for more than one receiver design but decreasing the transmitter’s standby power could save as much energy over a 24-h period as improving full-power efficiency by 10%.