Idle Power Loss Suppression in Magnetic Resonance Coupling Wireless Power Transfer

Abstract

We present a magnetic resonance coupling (MRC) wireless power transfer system that suppresses power losses when operating in an idle state while maintaining high transmission efficiency when operating in an active state. Maximum power can be transferred between transmitting and receiving resonant coils by designing for a simultaneous conjugate match at the source and the load. This match condition, however, leads to high power losses in the transmitting coil when the receiving coil is removed from the system (i.e., when the system is idle). In applications where a device is charged intermittently using a passive charger, the system should be designed by considering power losses in both active and idle states in order to maximize overall system efficiency over time. Here, we show that we can first reduce the idle power losses by introducing mismatch at the transmitter. We can then ensure high active transfer efficiency by introducing a compensating mismatch at the receiver. A four-coil MRC system was built to demonstrate the effectiveness of the idle power loss suppression. By retuning the source and receiver match, the idle power losses were reduced from 38% to 13%, while the active transfer efficiency only dropped from 85% to 76%.