Load-Independent Output Voltage Analysis of Multiple-Receiver Wireless Power Transfer System

The frequencies for load-independent output voltage in two-coil and three-coil wireless power transfer (WPT) systems have been studied. However, analysis of load-independent output voltage in multiple-receiver WPT is still lacking in previous studies. This letter investigates the output voltage characteristics of a multiple-receiver WPT system against load variations and determines the operating frequency to achieve a constant output voltage. First, a multiple-receiver WPT system is modeled, and the analytical expression of the root mean square of the output voltage is derived. By substituting the loaded quality factor and the coupling coefficient between each receiver and the transmitter, we determine the frequency for load-independent output voltage in multiple-receiver WPT for the first time. For the given multiple-receiver WPT system, although the load in each receiver is the same, the coupling coefficient between each receiver and the transmitter can be different. When the coupling coefficients are relatively small, there are two frequencies that can achieve load-independent output voltage. If the coupling coefficients increase and the quadratic sum of these coupling coefficients is greater than 1, only one frequency can achieve load-independent output voltage. Theoretical calculations and experimental results confirm these conclusions.