A Systematic Approach for Load Monitoring and Power Control in Wireless Power Transfer Systems Without Any Direct Output Measurement

A systematic method is presented in this paper to show that, based only on the measurements of the input voltage and current, the load impedance of a wireless power transfer system can be instantaneously monitored and load power controlled without using any direct measurement from the load. A new mathematic procedure for deriving the output load information based on input voltage and current is explained. This systematic method, which can be applied to wireless power systems with two or more coils, eliminates the need for sensors and communication devices on the load side, thereby greatly simplifying the power control circuitry. The principle of the load estimation method, the power loss optimization and control scheme are described and favorably verified with measurements obtained from an eight-coil wireless power transfer system.