A wireless power transfer system with a primary-side process variable for maximum efficiency control

This paper proposes a simple primary-side feedback-control approach that tracks maximum efficiency for a tuned-resonant inductive power transfer (IPT) system with a constant-power load. The control loop uses the voltage across a shunt capacitor in a primary-side LCL-T resonant converter (LCL-T RC) as a process variable. The key finding is that this voltage's AC amplitude can exhibit little variation over a wide-range of coupling coefficients k for a system operating at maximum efficiency with a constant power load. Therefore, this signal can be compared against a setpoint to drive a primary-side feedback controller for maximum efficiency tracking without the need for wireless feedback from the receiver. This technique is experimentally verified for a 2.5 W system with primary and secondary controllers acting independently without direct communication. The system maintains near-maximum power efficiency over the range 0.059 < k < 0.13.