Comparative Study of CCPT Systems With Two Different Inductor Tuning Positions

Capacitively coupled power transfer (CCPT) technology has been proposed and investigated as an alternative to inductive power transfer solution in certain low-power applications with the advantages of being able to transfer power across metal barriers and having low standing power losses. A series inductor is often used to compensate a CCPT system for the reactance introduced by the capacitive coupling, and there is a preconception that the tuning inductor can be placed either before or after the capacitive coupling without affecting the system performance. This paper develops a simple circuit model to enable the performance differences of placing such a tuning inductor on the primary and secondary sides of the circuit to be compared. The output voltage transfer function, voltage across the tuning inductor, displacement power factor, and total harmonic distortion are evaluated, and it is found that due to the existence of cross capacitive coupling there are significant differences in each of these performance indices when coupling variations are considered. The output voltage can be boosted, the misalignment tolerance can be improved, and the total harmonic distortion can be reduced when the tuning inductor is placed on the primary side of the circuit. The theoretical analysis is verified by experimental results.