DC-DC Converter Based Impedance Matching for Maximum Power Transfer of CPT System with High Efficiency

It is well known that a DC or fully tuned inductive power transfer (IPT) system operating at its maximum power output point results in a low power efficiency being equal or below 50%. Based on the analyses of the maximum power transfer condition against the detuning factor of an LC resonant circuit, this paper proposes a Capacitive Power Transfer (CPT) system which can track the maximum power output using a DC-DC converter, at the same time achieve a high-power efficiency when the circuit is not fully tuned. The method is applied to a voltage-fed inverter at series tuned off-resonance operation for reduced power losses. A prototype system is built with a half-bridge inverter to drive the capacitively coupling circuit, and a buck-boost converter is designed for impedance matching. A perturb and observe algorithm is developed for controlling the duty cycle of the DC-DC converter to track the maximum power against load variations. It is found that under a fixed electric field coupling condition, the system can maintain the maximum power transfer operation at 10W and achieve a power efficiency of about 70% over a wide range of load variation from 5\mathbf{\Omega} to 500\mathbf{\Omega}.