Analytical Models of Wireless Power Transfer Systems with a Constant-Power Load

Wireless Power Transfer (WPT) has attracted much attention in recent years. Voltage tuning and frequency tuning are two major tuning methods to control the output of a WPT system. For the design of a WPT system at the rated output power, it is crucial to analyze the WPT system with a constant-power load under voltage tuning and frequency tuning. The analytical models of a WPT system with a constant-power load both at and off the resonant frequency are established. The expressions of the transmitter current, the receiver current, the DC voltage of the rectifier, and the coil-to-coil efficiency are derived. The conditions to achieve the maximum coil-to-coil efficiency for voltage tuning and frequency tuning are obtained. An experimental prototype is implemented. The experimental results agree well with the analysis and the calculations. With a strong coupling, the maximum efficiency of frequency tuning can be as high as that of voltage tuning.