US Patent 10135303 Operating a wireless power transfer system at multiple frequencies

A transmitter device in an inductive energy transfer system includes a first transmitter coil operatively connected to a first resonant circuitry. A receiver device includes a first receiver coil operatively connected to a first resonant circuitry. The first transmitter coil and the first receiver coil form a first transformer. The transmitter device, the receiver device, or both the transmitter and receiver devices can also include an auxiliary coil or inductor, which may form an auxiliary transformer. Energy can be transferred from the transmitter device to the receiver device using the first transformer or the auxiliary transformer. The transfer of energy may be adaptively adjusted based on the efficiency of the energy transfer. For example, the transfer of energy can be adjusted based on the operating conditions of the load.