Wireless power transfer enables reliable energy delivery to fully embedded devices, eliminating the need for physical connectors while supporting device miniaturization. Flexible wireless power transfer systems extend this potential to applications requiring mechanical compliance, such as powering implantable medical devices in anatomically challenging locations with reduced foreign-body sensation. Capacitive power transfer is a near-field wireless power transfer method that is often cited as tolerant to bending deformations. However, this claim is based on limited evidence derived from studies on non-resonant systems or systems operating over larger distances, leaving the bending tolerance of resonant systems at small transfer distances largely unexplored. This work presents a systematic evaluation of bending on resonant capacitive power transfer at small distances, quantifying the impact of bending deformation on both the capacitive link and overall system performance. The results reveal that while concentric bending has negligible impact, outward receiver and inward transmitter bending significantly affect the system performance. AC-analysis measurements show that outward receiver bending shifts the optimal resonance frequency and reduces the power transfer efficiency by 54.5%. With inward transmitter bending, frequency splitting occurs which enhances the maximum power transfer efficiency with 8.5%. The findings redefine the bending robustness of capacitive power transfer systems and provide insight into their suitability for powering flexible applications.

ABSTRACT Maintaining a stable operating frequency while achieving robust power delivery remains a challenge in parity–time (PT)‐symmetric wireless power transfer systems, particularly under variable coupling conditions. While self‐oscillating PT‐symmetric inductive power transfer (IPT) systems can track bifurcation frequencies to sustain power delivered to the load (PDL), their operating frequency varies significantly with coupling, limiting practical applicability. This paper demonstrates that in capacitive power transfer (CPT) systems, one bifurcation frequency remains largely insensitive to coupling variations—a unique property attributed to the fact that the self‐capacitance and the corresponding resonant frequency vary with the mutual‐capacitance. We propose a frequency selection method that enables the system to operate persistently at this stable high‐frequency branch. Experimental results confirm that the implemented CPT system operates within 490–500 kHz across varying coupling conditions, while maintaining a stable PDL and power transfer efficiency of over 75% (up to 90% under optimal loads). This approach offers a viable solution for applications requiring both frequency stability and efficient power transfer.

The development of robust and efficient wireless charging systems is essential for the widespread adoption of electrification in the transport sector, e.g., Electric Vehicles (EVs). Capacitive Wireless Power Transfer (CWPT) has emerged as a promising alternative to inductive methods, offering advantages such as lower cost, lighter structure, and reduced electromagnetic interference. However, the performance of practical CWPT systems, particularly systems employing simple L-type compensation networks, is severely affected by coupling plate misalignment, which causes variations in coupling capacitance. These variations give rise to a pseudo-resonance phenomenon, wherein conventional controllers, such as traditional Sliding Mode Control, mistakenly regulate reactive power to zero at an off-resonant frequency, leading to a drastic collapse in active power transfer. To overcome this limitation, this paper introduces a novel Adaptive Sliding Mode Control (ASMC) framework augmented with an online Recursive Least Squares (RLS) observer for real-time estimation of the time-varying coupling capacitance. The proposed dual-loop control structure integrates an inner adaptive loop that accurately tracks capacitance changes and an outer sliding mode loop that dynamically adjusts the inverter switching frequency to sustain true resonant operation. A rigorous Lyapunov-based stability analysis confirms global convergence and robustness of the closed-loop system. Comprehensive MATLAB/Simulink R2025a simulations validate the proposed approach, demonstrating its capability to maintain zero reactive power and stable 35 kW power transfer with over 95% efficiency under dynamic misalignment conditions of up to 30%. In contrast, a conventional SMC approach experiences severe pseudo-resonant collapse, with output power degrading below 1 kW. These results conclusively highlight the effectiveness and necessity of the proposed ASMC-RLS strategy for achieving robust, misalignment-tolerant CWPT in high-power EV charging applications.

The increasing trend towards electrification in transportation highlights the potential for electric ships and the demand for safe, rapid charging systems. Underwater capacitive power transfer (UCPT) is considered a suitable solution due to its high power density potential. This article presents research on and optimization of UCPT for shore-to-ship charging in freshwater environments. It proposes a design for an insulation coupler and explores the influence of parasitic capacitance in the environment. This study demonstrates how the ship and shore impact the coupler’s coupling coefficient and mutual capacitance, thereby affecting the power and efficiency. Through theoretical calculations and finite element analysis, a kW-level UCPT coupler is designed. Experimental verification under different cases confirms the efficiency and constant current output characteristics, with superior performance observed when the coupler is positioned further away from the ship or shore. This study showcases the potential of UCPT to provide reliable and efficient power supply for electric ships, while emphasizing the importance of considering environmental factors and parasitic effects in system design and operation. These findings contribute to advancing UCPT technology and offer insights for further optimization to enhance practical applicability.

Abstract - Wireless charging technology for electric vehicles (EVs) is emerging as a revolutionary solution to address the limitations of traditional plug-in charging systems. It offers enhanced convenience, safety, and automation by enabling energy transfer without physical connectors. This paper provides a comprehensive overview of wireless charging technologies, focusing on the principles, classifications, and advancements in static, dynamic, and quasi-dynamic systems. The study examines the electromagnetic coupling mechanisms such as inductive power transfer (IPT), capacitive power transfer (CPT), and resonant inductive coupling (RIC), highlighting their advantages, limitations, and design considerations. The research also discusses the role of power electronics, control algorithms, and magnetic field alignment techniques in optimizing energy efficiency. A comparative evaluation of existing technologies is presented to demonstrate their performance in terms of transfer efficiency, cost, and interoperability. Furthermore, the paper explores research gaps, challenges, and potential future directions, emphasizing the need for standardization, material innovation, and smart-grid integration. The results underscore that while wireless charging is technically feasible, significant efforts are still required to achieve large-scale commercial adoption for both static and dynamic charging infrastructures. Key Words: Wireless Power Transfer, Electric Vehicles, Inductive Charging, Dynamic Charging, Resonant Coupling.

ABSTRACTThe demand for high‐power wireless power transfer (WPT) systems has been increasing in recent years. However, most of the available research works on high‐power transfer are focused on inductive power transfer (IPT) systems. Compared with IPT, capacitive power transfer (CPT) offers advantages such as light weight, low cost, and simple structure. In this paper, the design and efficiency optimization method of a high‐power CPT system is proposed. Firstly, an input‐parallel output‐parallel (IPOP) multi‐channel topology is established for high‐power CPT systems, and the transmission characteristics are analyzed. A multi‐channel coupler with shielding plates is designed, and the equivalent circuit model of the coupler is developed based on the induced current source model. Then, the factors affecting efficiency are investigated, and an optimization method is proposed to enhance the overall system efficiency. Finally, an experimental platform of a 10‐kW IPOP three‐channel CPT system is built. Experimental results show that the output power is three times that of a single‐channel CPT system, with a dc–dc efficiency of 94.2%. The correctness and effectiveness of the design and optimization method are validated.

In this study, we investigate a shielded capacitive power transfer (S-CPT) system that employs cast iron road covers as transmission electrodes for both dynamic and static charging of electric vehicles. Coupling capacitance was evaluated from S-parameters using copper, aluminum, ductile cast iron, structural steel, and carbon steel electrodes, with additional comparisons of ductile iron surface conditions (casting, machining, electrocoating). In a four-plate S-CPT system operating at 13.56 MHz, capacitance decreased with electrode spacing, yet ductile cast iron reached ~70 pF at 2 mm, demonstrating a performance comparable to that of copper and aluminum despite having higher resistivity and permeability. Power transmission experiments using a Ø330 mm cast iron cover meeting road load standards achieved 58% efficiency at 100 W, maintained around 40% efficiency at power levels above 200 W, and retained 45% efficiency under 200 mm lateral displacement, confirming robust dynamic performance. Simulations showed that shield electrodes enhance grounding, stabilize potential, and reduce return-path impedance. Finite element analysis confirmed that the ductile cast iron electrodes can withstand a 25-ton design load. The proposed S-CPT concept integrates an existing cast iron infrastructure with thin aluminum receiving plates, enabling high efficiency, mechanical durability, EMI mitigation, and reduced installation costs, offering a cost-effective approach to urban wireless charging.

Although inductive power transfer (IPT) systems dominate the wireless power transfer (WPT) technologies, recently capacitive power transfer (CPT) systems also have received significant attention due to their outstanding benefits such as negligible eddy- current loss, higher reliability, better misalignment performance, lower cost, lightweight, and lower EMI . The CPT technology has many application areas in wireless charging concept. The first example that comes to mind for large transfer distance applications is the wireless electric vehicle (EV) charging . In addition, the effects of dielectric materials on capacitive coupler structures have great importance for increasing the power transfer capability and electric field strength . here three or four metal plate is proposed for EV charging applications . Herein, the chassis of a vehicle and earth ground are high- lighted to substitute for three or four plates used in conventional six plate structures. In addition, a three or four plate capacitive coupler structure provides a decreased number of plates and cost reduction in CPT applications. Then, three or four plate coupler structure to provide less electric field emission for large transfer distance applications. Nevertheless, the number of coupling capacitances to realize the equivalent circuit and increased cost with six metal plates are the drawbacks. the last conventional capacitive coupler structure called as an electric field repeater to enhance the transfer distance in CPT systems. However, the low system efficiency is the disadvantage of the coupler.

Although inductive power transfer (IPT) systems dominate the wireless power transfer (WPT) technologies, recently capacitive power transfer (CPT) systems also have received significant attention due to their outstanding benefits such as negligible eddy- current loss, higher reliability, better misalignment performance, lower cost, lightweight, and lower EMI . The CPT technology has many application areas in wireless charging concept. The first example that comes to mind for large transfer distance applications is the wireless electric vehicle (EV) charging . In addition, the effects of dielectric materials on capacitive coupler structures have great importance for increasing the power transfer capability and electric field strength . here three or four metal plate is proposed for EV charging applications . Herein, the chassis of a vehicle and earth ground are high- lighted to substitute for three or four plates used in conventional six plate structures. In addition, a three or four plate capacitive coupler structure provides a decreased number of plates and cost reduction in CPT applications. Then, three or four plate coupler structure to provide less electric field emission for large transfer distance applications. Nevertheless, the number of coupling capacitances to realize the equivalent circuit and increased cost with six metal plates are the drawbacks. the last conventional capacitive coupler structure called as an electric field repeater to enhance the transfer distance in CPT systems. However, the low system efficiency is the disadvantage of the coupler.

Highly Integrated Hybrid Inductive and Capacitive Power Transfer System With Asymmetrical Printed-Circuit-Board-Based Self-Resonator

An Electrified Tramway Wireless Charging System for Rail Transportation Using Dynamic Capacitive Power Transfer With Four Vertical Plates

ABSTRACTCapacitive wireless power transfer shows promise for wireless energy delivery, utilizing capacitive coupling for transmission. Quantifying the coupling between individual transmitters and receivers is essential, as optimization techniques for optimal output impedance depend on accurate knowledge of the coupling coefficient. Because practical capacitive power transfer systems often experience variations in distance or alignment, impacting the coupling coefficient and consequently, the optimal output impedance, it is desired to constantly measure the coupling coefficient. However, existing methods for measuring mutual capacitance in CPT systems require specific conditions, making them unsuitable for live measurements. This paper introduces a method for live calculation of mutual capacitance in CPT systems, applicable during normal operation. We present a theoretical framework applicable to SIMO systems with an arbitrary number of receivers and validate our results experimentally for both SISO and SIMO systems using a 10‐W prototype operating at a frequency of MHz. Our method shows strong agreement with established techniques, especially for systems with identical receivers. This approach enables live mutual capacitance calculation based on voltages and currents available during normal system operation. It is effective for SISO and SIMO configurations, confirmed by simulations and experiments.

This paper proposes a 1000 W high-frequency three-phase power inversion underwater capacitive wireless power transfer (UCWPT) system for power delivery to autonomous underwater vehicles (AUVs). The multi-phase coupling structure is designed as a columnar configuration that conforms to the shape of AUVs. This paper innovatively presents a curved coupling coupler composed of six metal plates. This design significantly enhances the mutual capacitance of the coupling structure and the power transfer capacity of the UCWPT system. Utilizing the columnar structure, the receiver of the capacitive wireless power transfer system can be easily integrated into AUVs, reducing the installation space. Furthermore, the cylindrical dock-transmitter terminal structure of the system greatly improves the anti-misalignment capability. This addresses issues such as charging voltage and current fluctuations caused by vehicle rolling in dynamic ocean environments. Additionally, the wireless power transfer capacity is notably enhanced. An experimental platform was constructed, and tests were conducted in both air and water media. A 1000 W experimental setup was developed to validate the theoretical analysis and simulations. The experimental results align closely with the theoretical predictions. At a fixed distance of 3 cm between transmitter and receiver, peak power transfer efficiencies of 80% in air and 74% in water were achieved with stable operational performance. The cylindrical structure demonstrates robust anti-misalignment properties.

This study analyzed the modeling and characteristics of parallel-plate capacitors for underwater capacitive wireless power transfer (CWPT) systems. Using finite element method (FEM) simulations, this study investigated the impact of various factors on the simulation results for both capacitance and conductance. A fitting equation is proposed for the coupling capacitance and conductance in a seawater environment. The derived equations were verified by varying the coupler size. For four different sizes, the maximum error percentage for capacitance was 9.18% at a size of 180×100 mm. For conductance, all error percentages were less than 3.49% at a transfer distance of 20 mm. The agreement between the simulated results and those calculated from the derived equations confirms the validity of the derived equations for both capacitance and conductance. Notably, this study also demonstrates a ratio of approximately 295.9 between the real and imaginary parts of the coupling admittance at a frequency of 3 MHz. This finding confirms that conductance, rather than susceptance, dominates the CWPT systems in underwater applications.

ABSTRACTIn underwater environments, existing capacitive power transfer (CPT) systems only consider the capacitance or conductivity of the coupling plate when analyzing transfer efficiency. This is inconsistent with the characteristics of the underwater coupler. Thus, it would lead to inaccurate efficiency models and difficult efficiency optimization design. To address the above issue, this paper models the underwater CPT system by simultaneously considering the capacitance and conductivity of the coupler in the efficiency model, so a more accurate efficiency model of CPT system in the underwater environment is derived. On this basis, the efficiency optimization design of the underwater CPT system is carried out, and the optimization design process is provided. Finally, the accuracy of the proposed efficiency model and the effectiveness of the design method have been demonstrated through simulation and experimentation. With the proposed optimization method, the underwater CPT system achieves a transfer efficiency of 82% within a load range of 10 Ω to 60 Ω at a plate spacing of 100 mm. The maximum transfer efficiency reaches 90%.

A Novel Comb-Shaped Coupler for Hybrid Inductive and Capacitive Wireless Power Transfer System

Stabilization Control of Output Voltage for Segmented Dynamic Capacitive Power Transfer System Based on Partial Power Processing

A Critical Review of Compensation Converters for Capacitive Power Transfer in Wireless Electric Vehicle Charging Circuit Topologies

This work aims to present an innovative design and simulation of an auto-tuning capacitive power transfer (CPT) system. The system utilizes a Class-E converter, renowned for its exceptional efficiency. Challenges arise when trying to regulate the output voltage of a Class-E converter in the presence of load fluctuations, leading to an escalation in switching losses. By employing first harmonic approximation (FHA) and generalized state space averaging (GSSA), a state-space model of the system is constructed to effectively address this problem. The output voltage is regulated by a state feedback controller developed using the Lyapunov approach. This paper presents a comparative analysis of a traditional PID controller and a recently suggested state feedback controller, with a primary emphasis on system stabilization. The study examines the similarities and differences between the two controllers. The efficacy of the proposed controller design is demonstrated through the utilization of simulation data. Furthermore, these results confirm the validity of the comparative study, making it a substantial contribution to the field of CPT systems.

Modeling and Analysis of Undersea Capacitive Power Transfer Based on Conduction Current in Seawater