The rapid development of power electronics technology and wireless power transmission (WPT) has broadened application prospects in consumer electronics and traditional fields like electric vehicles, implantable medical devices, and autonomous underwater vehicles. The unique nature of wireless charging scenarios often results in significant variations in transmission distance, causing rapid drops in coupling coefficient and transmission efficiency. Therefore, coil compensation is an important research area of WPT. This paper proposes a segmented coil compensation method using inter-turn capacitance to solve increased internal voltage gradients in coils caused by traditional external capacitor compensation methods. By closely fitting the adjacent turns of the receiving coil, the capacitance of the closely fitting section is increased, thereby achieving coil compensation. The coil is divided into several segments, with inter-turn capacitance to compensate for each segment.

First, the advantages of segmented coil compensation are derived using rigorous circuit theory. Next, equivalent modeling and calculation of the Litz wire wound coil are performed to analyze the factors influencing the size of the inter-turn capacitance. Finally, the overall coil with inter-turn capacitance segmented compensation is modeled, and the port impedance of the entire coil is calculated. The inter-turn capacitance of the closely fitting coil segments increases significantly, effectively replacing the external capacitors for compensation. Compared to external capacitor compensation topologies, the proposed segmented compensation topology can reduce the internal voltage gradient of the coil, voltage loss, and energy dissipation. Accordingly, the energy reception efficiency of the coil is improved. Additionally, this structure is compact, with a small size and cost.

An experimental coil is compared with a coil using external capacitor compensation. Under the same input and load conditions, the receiving power of the coil with the proposed segmented compensation is increased by 54.3%, and efficiency is improved by 27.6%, which verifies the proposed method.

The following conclusions can be drawn. (1) The tight alignment length of the turns and the dielectric constant of the wire insulation layer influence the inter-turn capacitance. When Litz wire is used for equivalent analysis, the inter-turn capacitance increases significantly with the tight alignment length and shows a linear growth trend. The capacitance also increases significantly as the equivalent dielectric constant of the insulation layer increases, effectively compensating the coil. (2) Inter-turn capacitance compensation provides adequate compensation. Compared to traditional concentrated compensation methods, the proposed segmented compensation reduces the internal voltage gradient of the coil, decreases voltage losses and energy dissipation, and enhances the energy reception efficiency of the coil.