Wireless Power Transfer With Automatic Feedback Control of Load Resistance Transformation

This paper proposes a wireless power transfer with automatic feedback control of load resistance transformation to maintain high efficiency over wide variations of coupling current and load current. The receiver (Rx) first determines the desired current level of transmitter (Tx) coil such that the receiver-side converter can transform the load resistance into optimum effective resistance, based on load current and Tx-to-Rx distance information. The determined Tx coil current data are sent to the transmitter, which then adjusts the Tx coil current accordingly. In this way, the effective resistance transformed by the receiver-side converter remains optimum under the variations of distance and load current. One of the advantages of the proposed automatic feedback control is faster response and simple hardware because it does not use operating point sweep and observation. The receiver-side switching converter also incorporates the ability to send data from receiver to transmitter by modulating the duty cycle of converter at data frequency, eliminating the need for separate RF communication hardware. This proposed communication does not require shunt current dissipation from dc output to ground, resulting in low loss. Experimental result demonstrates that the system maintains high efficiency under wide variations of coupling and load current.