Natural Frequency Optimization of Wireless Power Systems on Power Transmission Lines.

Optimizing the natural frequency is crucial for dc-to-load efficient wireless power transfer (WPT) applications on high voltage (HV) power transmission lines. However, a comprehensive optimization approach with the coupling factor and the losses on power electronics both taken into consideration is still in absence. By modeling losses dissipated on various parts, including the class-D inverter, the rectifier, and the resonant loops, a numerical approach is proposed in this paper to evaluate the optimal natural frequency for maximum dc-to-end efficiency. As the system efficiency is also affected by the operating frequency, which is resilient for practical operation, practical operating strategies are applied to determine the working parameters. Furthermore, considering that the HV WPT systems may work with various coupling factors, optimal natural frequencies for various coupling factors are analyzed and compared. Several groups of experiments are conducted to verify the effectiveness of the proposed numerical approach. Experimental results show that the approach can effectively predict the optimal natural frequency. When compared with the cases where the natural frequency is 100 or 600 kHz, an efficiency enhancement of about 20% can be achieved using the optimized natural frequency. When compared with the cases where the natural frequency is optimal for maximum Q value, an efficiency of 9% can still be achieved for loosely coupled occasions.