A Variable Frequency Control (VFC)-based WPT System Featuring Constant Voltage Output, Less Power Stages, and Lower System Costs

Many compensation topologies showing the characteristic of constant voltage output (CVO) have been proposed for wireless power transfer (WPT) systems. However, the output voltages of practical WPT systems using these compensation topologies are not constant due to the influence of input voltage variations, parasitic resistance, parameter errors, and duty cycle loss at light load. To handle with this problem without adding an extra DC-DC converter, variable frequency control (VFC) is introduced into WPT systems. Series-series topology with leakage inductance compensation (SS-LIC) is utilized in this research as it requires only two capacitors. The CVO characteristic of SS-LIC is deduced using fundamental harmonic analysis method. The frequency response of the WPT system utilizing SS-LIC is studied. The determination of operating frequency range was also investigated. PSpice simulations were conducted. The output characteristics with and without VFC were compared. The validity of the proposed voltage regulation method was corroborated. A WPT prototype was built to verify the rightness of theoretical analysis and simulation results. Experiment results agree well with simulation ones, demonstrating the feasibility of the proposed VFC control in WPT systems.