A double-sided LCLC-compensated capacitive power transfer (CPT) system is proposed for the electric vehicle charging application. Two pairs of metal plates are utilized to form two coupling capacitors to transfer power wirelessly. The LCLC-compensated structure can dramatically reduce the voltage stress on the coupling capacitors and maintain unity power factor at both the input and output. A 2.4-kW CPT system is designed with four 610-mm × 610-mm copper plates and an air gap distance of 150 mm. The experimental prototype reaches a dc-dc efficiency of 90.8% at 2.4-kW output power. At 300-mm misalignment case, the output power drops to 2.1 kW with 90.7% efficiency. With a 300-mm air gap distance, the output power drops to 1.6 kW with 89.1% efficiency.

This paper proposes a four-plate compact capacitive coupler and its circuit model for large air-gap distance capacitive power transfer (CPT). The four plates are arranged vertically, instead of horizontally, to save space in the electric vehicle charging application. The two plates that are on the same side are placed close to each other to maintain a large coupling capacitance, and they are of different sizes to maintain the coupling between the primary and secondary sides. The circuit model of the coupler is presented, considering all six coupling capacitors. The LCL compensation topology is used to resonate with the coupler and provide high voltage on the plates to transfer high power. The circuit model of the coupler is simplified to design the parameters of the compensation circuit. Finite-element analysis is employed to simulate the coupling capacitance and design the dimensions of the coupler. The circuit performance is simulated in LTspice to design the specific parameter values. A prototype of the CPT system was designed and constructed with the proposed vertical plate structure. The prototype achieved an efficiency of 85.87% at 1.88-kW output power with a 150-mm air-gap distance.

This paper proposes a continuous dynamic wireless power transfer system for electric vehicles that reduces power pulsations during the charging process. Multiple rectangular unipolar coils are used at the primary side as the transmitters, and another unipolar coil works as a receiver at the secondary side. The transmitters are placed closely together to reduce the variation of magnetic fields along the moving track of the receiver. This structure induces self-coupling between the adjacent transmitters. An LCC-compensated circuit topology is utilized, and a compensation parameter design is provided which considers self-coupling between the primary coils. Finite-element analysis of the dynamic charging system is performed using Maxwell. The receiver size is optimized to reduce the variation of the coupling coefficient. A 1.4-kW dynamic charging prototype is constructed according to the designed coil structure and circuit parameters. There are six transmitters, each with dimensions 388 mm×400 mm, and one receiver with dimensions 485 mm×400 mm. Experimental results show that the output power pulsation is within ±7.5% in the dynamic charging process, and the maximum efficiency is 89.78%. If the edge effects of the transmitters are neglected, then the power pulsation is within ±2.9%.

Capacitive power transfer (CPT) technology is an effective and important alternative to the conventional inductive power transfer (IPT). It utilizes high-frequency electric fields to transfer electric power, which has three distinguishing advantages: negligible eddy-current loss, relatively low cost and weight, and excellent misalignment performance. In recent years, the power level and efficiency of CPT systems has been significantly improved and has reached the power level suitable for electric vehicle charging applications. This paper reviews the latest developments in CPT technology, focusing on two key technologies: the compensation circuit topology and the capacitive coupler structure. The comparison with the IPT system and some critical issues in practical applications are also discussed. Based on these analyses, the future research direction can be developed and the applications of the CPT technology can be promoted.

This paper proposes a double-sided LC-compensation circuit for a loosely coupled, long-distance capacitive power transfer (CPT) system. A CPT system usually contains two pairs of metal plates as the capacitive coupler. An LC-compensation circuit resonates with the coupler to generate high voltages, and corresponding electric fields, to transfer power. When the compensation circuit is used on both the primary and secondary sides, it results in a double-sided LC-compensated CPT system. The working principle and frequency properties of the CPT system are analyzed. The results show a similarity with the series-series-compensated inductive power transfer system, which has both constant-voltage (CV) and constant-current (CC) working modes. LC-compensation is also compared with LCLC -compensation in terms of power, frequency properties, and output efficiency. A 150-W double-sided LC -compensated CPT prototype is designed and implemented to demonstrate a loosely coupled CPT system with 2.16% coupling coefficient. For both CC and CV working modes, the experimental results achieve dc-dc efficiencies higher than 70% across an air-gap distance of 180 mm with a switching frequency of 1.5 MHz.

Wireless Power Transfer (WPT) has attracted much attention in recent years. In an underwater WPT system, the eddy current loss tends to be non-negligible as the frequency or the coil current increases. Thus, it is crucial to analyze the eddy current loss in an underwater WPT system. The analytical model of the eddy current loss of a coreless WPT system in the seawater is established with Maxwell's equations. The expressions of the electric field intensity and the eddy current loss are derived. The eddy current loss is analyzed in different circumstances to illustrate the impacts of related factors. For a WPT system in the air, there is an optimum resonant frequency, a higher frequency leads to a larger induced voltage, but will result in larger coil losses simultaneously. However, the optimum resonant frequency will be shifted for the eddy current loss in the seawater. Then the optimum operating frequency is obtained based on the analytical model. It is found that the optimum operating frequency is supposed to be larger than the resonant frequency to achieve the maximum DC-DC efficiency in the seawater. An underwater WPT prototype was built and the experimental results verified the theoretical analysis.