Variable-distance wireless-power-transfer system with fixed tuning and power limiting

A wireless-power-transfer system comprising:

• a transmitter circuit including:
• a DC input;
• an oscillator-controlled drive stage connected to the DC input and providing an output at a fixed frequency;
• a primary series-resonant capacitor connected to the oscillator-controlled drive stage;
• and
• a transmitting coil connected to the primary series-resonant capacitor;
• wherein
• a transmitting resonant frequency is defined by the primary series-resonant capacitor and the transmitting coil;
• and
• the transmitting resonant frequency is below the fixed frequency of the oscillator-controlled drive stage;
• and
• a receiver circuit including:
• a receiving coil;
• a secondary series-resonant capacitor connected in series with the receiving coil;
• a secondary parallel-resonant capacitor connected in parallel with the receiving coil;
• a rectifier circuit connected to the secondary series-resonant capacitor and the secondary parallel-resonant capacitor and including at least one rectifier;
• and
• an output filter capacitor connected to the rectifier circuit and arranged to receive a rectifier-circuit DC output;
• wherein
• a receiving resonant frequency is defined by the secondary series-resonant capacitor, the secondary parallel-resonant capacitor, the receiving coil, and a nonlinear capacitance of the at least one rectifier;
• and
• the receiving resonant frequency increases as a nonlinear capacitance of the at least one rectifier decreases when the rectifier-circuit DC output increases.