A method of controlling a wireless power transfer system comprising a primary stage and a secondary stage is provided. The primary stage comprises a DC/DC converter configured to generate a DC output, a DC/AC inverter configured to receive the DC output and to generate an AC output according to a variable switching frequency, and a primary coil configured to transfer power to the secondary stage in response to the DC/AC inverter generating the AC output. The switching frequency of the DC/AC inverter is adjusted to cause a phase angle between an input current and an input voltage of the primary coil to be less than or equal to a predetermined threshold. The DC output of the DC/DC converter is controlled to cause a desired amount of power to be transferred from the primary coil at the adjusted switching frequency.