Synchronous Rectification Through Sense Coil in HF-IPT Systems

This manuscript presents the design and development of a synchronous rectification technique for high frequency inductive power transfer systems which is based on a sense coil.The idea of using a sense coil has been widely discussed for several applications in wireless power transfer. In the literature a sense coil is also used to achieve synchronisation of a bidirectional wireless power transfer system operating in the tens-of-kilohertz range. This solution is viable when it is possible to accurately subtract part of the slave-side coil current from the sense coil to achieve frequency locking between the two sides of the system; however, operation of an IPT system in the megahertz range comes with challenges associated with the required instrumentation to perform current sensing of an operating IPT coil. A possible solution proposed in this manuscript is to decouple the sense coil from the secondary to achieve synchronisation without the need of sensing the current on the slave side.The proposed system is based on a 13.56 MHz back-to-back Class EF configuration with bidirectional capabilities thanks to a source-sink configuration of the input DC voltage of the transceivers using an electronic load in constant voltage mode in parallel with a power supply. The synchronisation of the switching frequency of the slave side of the system is achieved by deploying a sense coil that is decoupled from the slave-side coil and highly coupled with the master-side coil, hence providing a stable frequency reference across the two sides of the system. Phase synchronisation is achieved using a variable delay module to achieve zero reflected reactance, and hence a phase shift between the currents in the coils of the transceivers close to 90°. The system was tested for different low-coupling scenarios, achieving an output power of 10.1 W with 45% efficiency for a coupling of 4.1%, 6 W with 34% efficiency for a coupling of 2.8% and 2.8 W with 5% efficiency for a coupling of 1.9%.