Large Air-gap Capacitive Power Transfer Research Articles

A Circuit Design Method for Constant Voltage Output With Zero Phase Angle and Minimum Coupler Voltages in Capacitive Power Transfer

Constant output characteristics, zero phase angle (ZPA), and coupler voltage stresses as low as possible are practical requirements for high power and large air-gap capacitive power transfer (CPT) applications. This article derives conditions of load-independent constant voltage output, ZPA, and minimum coupler voltages for general CPT systems, respectively. Minimum degrees of freedom (DOF) for the above performance are analyzed. Given performance requirements, a systematic circuit design method based on DOF analysis is proposed to design compensation circuits with fewer components to simplify complexity and decrease costs. The proposed method can predict feasible topologies, and application considerations are provided to guide topology selection. A 3 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> -compensated CPT system is proposed to realize the constant voltage output with ZPA, minimum coupler voltages, and efficiency optimization. A 2.2 kW CPT prototype has been prepared with a 250 mm air-gap distance and dc–dc efficiency is 87.2%. Rms values of coupler voltages are about 5 kV at the rated power.

Six-Plate Capacitive Coupler to Reduce Electric Field Emission in Large Air-Gap Capacitive Power Transfer

This paper proposes a six-plate capacitive coupler for large air-gap capacitive power transfer to reduce electric field emissions to the surrounding environment. Compared to the conventional four-plate horizontal structure, the six-plate coupler contains two additional plates above and below the inner four-plate coupler to provide a shielding effect. Since there is a capacitive coupling between every two plates, the six-plate coupler results in a circuit model consisting of 15 coupling capacitors. This complex model is first simplified to an equivalent three-port circuit model, and then to a two-port circuit model which is used in circuit analysis and parameter design. This six-plate coupler can eliminate the external parallel capacitor in the previous LCLC topology, which results in the LCL compensation and reduces the system cost. Due to the symmetry of the coupler structure, the voltage between shielding plates is limited, which reduces electric field emissions. Finite element analysis by Maxwell is used to simulate the coupling capacitors and electric field distribution. Compared to the four-plate horizontal and vertical structures, the six-plate coupler can significantly reduce electric field emissions and expand the safety area from 0.9 to 0.1 m away from the coupler in the well-aligned case. A 1.97 kW prototype is implemented to validate the six-plate coupler, which achieves a power density of 1.95 kW/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and a dc-dc efficiency of 91.6% at an air-gap of 150 mm. Experiments also show that the output power maintains 65% of the well-aligned value at 300 mm X misalignment, and 49% at 300 mm Y misalignment.