Power and efficiency are two important indexes for power transmission systems. By theoretical analysis combined with experiments

the transmission characteristics of power and efficiency for the wireless power transmission system based on magnetic resonance coupling are researched. The results show that there is the bifurcating phenomenon in both the bearing power and the frequency response curves of system efficiency. The bearing power and frequency response curves of a transmitting system with identical parameters at the transmitting and receiving terminals appear to be approximately symmetric in shape. The bearing power before bifurcation vanishes does not vary with the change in distance between transmitting and receiving terminals. There is the difference between the primary and secondary resonance frequencies when the frequency is bifurcated for asymmetrical systems

and the bearing power will be enhanced first and then declined with an increase in the transmission distance. Mathematical expressions for critical coupling coefficient and transmitting and receiving terminals optimization coupling coefficient for optimal power transmission are deduced. In view of the feature that the peak power and peak efficiency working frequency points do not coincide

an information feedback-based energy efficiency optimal control strategy is proposed. In addition

by the aid of the energy transmitting channel

the work state is fed back to the transmitting terminal using the load modulating technique to realize closed loop control of the energy transmission process. The conclusions drawn in the paper are in agreement with experimental results. This work is supported by National Natural Science Foundation of China (No. 61403201).