Compensation Network Design of CPT Systems for Achieving Maximum Power Transfer Under Coupling Voltage Constraints

It is well known that a high voltage across the coupling plates of a capacitive power transfer (CPT) system is beneficial to increase its power transfer capability, but a high voltage may lead to high insulation requirements and cause safety concerns. This article proposes a compensation design method for achieving the maximum power of CPT systems under coupling voltage constraints. Based on a simplified capacitive coupling model and thorough power transfer characteristics analysis, a family of compensation topologies are derived to maintain a 90° phase shift between the input and output voltages across the CPT coupler against load variations, so that the coupling voltages (which practically need to be limited) are fully utilized for power transfer purposes. A full design process for determining the compensation parameters is presented, and an example 2-kW CPT system is built and tested using
LC
compensation at the primary side to boost the input voltage to the coupler; and one of the proposed compensation topologies (CLC) at the secondary side for impedance transformation of a given load with a specified voltage and power requirements. Experimental results show a good agreement with theoretical analysis, which demonstrate the phase difference between the voltages before and after the coupler is kept nearly 90°, and a maximum possible power transfer of 2.039 kW is achieved under the given voltage limits and coupling conditions. A system end-to-end (dc–dc) efficiency of 90.29% is obtained when the air gap between the coupling plates is 150 mm, and the coupling capacitance is only 13.84 pF.