Phase-shift and amplitude control for an active rectifier to maximize the efficiency and extracted power of a Wireless Power Transfer system

Wireless Power Transfer (WPT) is an emerging technology with a huge variety of possible applications, including wireless charging of mobile devices like smart-phones or tablet computers. Currently available systems targeting these applications achieve a relatively low efficiency and hence a limited charging capability. To overcome these drawbacks, this work proposes a concept to maximize the efficiency of a WPT system as well as to increase the amount of extracted power. The presented method is based on actively modifying the equivalent secondary-side load impedance by controlling the phase-shift of the active rectifier and its output voltage level. The proposed concept enables WPT systems to actively adjust both the resistive as well as the reactive part of the equivalent load impedance, hence increasing the system performance in terms of efficiency and extracted power. A prototyping system for mobile applications has been developed based on the Qi standard specifications. The acquired experimental results confirm that the proposed concept is able to obtain a higher system efficiency and to extract more power than state-of-the-art solutions.