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Fine Tuning of an Inductive Link Through a Voltage-Controlled Capacitance

Wireless power transfer is a technique usually based on an inductive link, used for delivering energy to remote devices. The power of different applications ranges from microwatts to hundreds of kilowatts, e.g., in biomedical implants and electric vehicles. The transferred power is highly dependent on the relative position between the inductive link coils. Many studies have been presented considering static or quasi-static conditions, based on a fixed tuned circuit. However, when the coils are not stationary, the inductive link must be dynamically tuned to keep the designed output power. This paper presents a methodology for dynamically tune the inductive link by means of a variable capacitance. A voltage-controlled capacitance using concepts of the negative impedance converter and capacitance multiplier is proposed. The phase angle between the input voltage and current is used as the error signal to control the variable capacitance and keep the output power operating point. The experimental evaluation shows that the proposed methodology can significantly improve the power delivered to the load in comparison to a fixed inductive link.