STUDY OF THE FREQUENCY CHARACTERISTIC FOR A MAGNETICALLY COUPLED RESONANT WIRELESS POWER TRANSMISSION SYSTEM WITH CHANGES OF THE CAPACITANCE

The resonant frequency of a magnetically coupled resonant wireless power transmission system is a core parameter that determines the performance of the system. However, how to obtain the variation law of the resonant frequency and the efficiency or output power of the system is still a difficult problem when the capacitance of each coil is changed. In this paper, a two-coil wireless power transmission system is taken as an object, and the expressions of the input impedance, frequency, efficiency, and output power are deduced. Based on these expressions, the relationships among frequency, efficiency, and output power are studied. It is concluded that there may be multiple resonant frequencies in s WPT system with the changes of capacitance. The system always features a maximum efficiency point and a maximum output power point. The frequencies of the two points are almost the same. These theories provide a feasible scheme for simultaneously achieving both a high efficiency and output power. Finally, a magnetically coupled resonant wireless power transmission system is designed and developed. Simulated and experimental results demonstrate the validity and correctness of the proposed method.