This paper presents a sleeve-type capacitive power transfer (CPT) system for contactless rotary applications. Sleeve-type capacitive couplers with different coupling arrangements between primary and secondary metal sleeves are proposed in this research, which lead to different coupling characteristics with positive, zero, and negative coupling coefficients. The effect of coupling coefficient variations caused by both the power transfer distance and the ratio between the overlapping length and the height of outer sleeves is analyzed. Combining the sleeve-type coupler, the CPT system is developed with a double-sided LCcompensated network and half-bridge inverter. For the CPT systems with positive and negative coupling coefficients, parameter design methods are presented to determine system parameters to achieve zero phase angle (ZPA) condition under the same output power. Then overall system performances of the CPT systems with local maximum positive and local minimum negative coupling coefficients are analyzed and compared by simulation in MATLAB/Simulink and Maxwell. Finally, an experimental prototype is constructed, which has demonstrated a power efficiency of 85.3% at 100.8 W. Simulation and experimental results show that the CPT system with local minimum negative coupling coefficient has clear advantages in increasing transfer distance, reducing voltage on sleeves, suppressing fringing electric field, and improving power density.INDEX TERMS Wireless power transfer, capacitive power transfer, sleeve-type capacitive coupler, negative coupling coefficients.
In this paper, possible coupling configurations of a four-plate capacitive power transfer system are studied by varying the combinations of its input and output ports. A voltage source is applied between two of the four plates, and a load is connected to the other two to form different circuit topologies. A mathematical model based on a 4 × 4 mutual capacitance matrix is established for equidistantly placed four identical metal plates. Based on the proposed model, four separate circuit topologies are identified and analysed in detail and described in a general form. The electric field distributions of the coupling configurations are simulated by ANSYS Maxwell. The theoretical modeling and analysis are then verified by a practical system, in which four aluminum plates of 300 mm × 300 mm are used and placed with a gap of 10 mm between adjacent plates. The experimental results show that the measured output voltage and power under the four coupling configurations are in good agreement with the theoretical results. It has found that the voltage gain is the highest when the two inner plates are connected to the source, and this coupling configuration also has the lowest leakage electric field.
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