In magnetic coupling wireless power transfer systems, air gap and load changes are very common. Due to the presence of ferrite cores, changes in the air gap can lead to variations in coil parameters (mutual inductance and self-inductances), particularly in small air gap applications. This article proposes a constant current (CC) output method for LCC-LCC compensated WPT system with variable parameters. The proposed method utilizes an integrated magnetic coupler to provide a variable compensation inductance to offset output fluctuations caused by mutual inductance changes. In addition, compensation parameters for maintaining a CC output versus air gap and load changes are obtained through a particle swarm optimization (PSO) algorithm. An 800 W experimental setup is constructed to validate the effectiveness of the proposed method. The experimental results show that, when the output power varies from 400 to 800 W, within the air gap range of 15 to 50 mm, with a maximum self-inductance variation range of 23% and a maximum coupling coefficient variation range of 0.71 to 0.32, the system has a CC output characteristic with a maximum current fluctuation of only 4% and a maximum efficiency of 90.8%. A video demonstrating the variations in system key waveforms during air gap changes is attached to this article.

In wireless power transfer (WPT) systems, changes in air gaps are inevitable, which can cause drift of mutual inductance and self-inductance parameters, leading to a decrease in output power and efficiency. In this paper, a wide coupling range zero voltage switching (ZVS) implementation method with phase shift control (PSC) is proposed, which improves the system efficiency while achieving constant voltage (CV) output characteristics. Based on the time domain model analysis of the inductor–capacitor–capacitor-series (LCC-S) topology, the influence law of coil self-inductance variation on the implementation of ZVS is obtained. The magnetic coupler was designed and the parameters were optimized to realize the ZVS operation with the range of air gap variation of 10~60mm, mutual inductance variation of 21~85μH, maximum self-inductance variation of 80.5~139μH, coupling coefficient variation of 0.2~0.6, and minimum reactive current.

The magnetic coupling wireless power transfer (MC-WPT) system for automatic guided vehicles is characterized by a small and unfixed air gap, which leads to significant changes in self- and mutual inductance of the magnetic coupler. In this article, an efficiency improvement method is proposed for the MC-WPT system with variable self- and mutual inductance parameters. By optimizing the design of magnetic couplers and compensation parameters, a wide range of zero-voltage switching (ZVS) operation and minimization of the reactive current are achieved. The self-inductance variation is utilized to provide a variable system input impedance, which expands the ZVS operation range with phase-shift modulation. Meanwhile, the reactive current of the resonant tank in the entire air gap range can be reduced to the minimum when the tuning parameters are designed properly. Compared with the traditional hybrid control strategies, the proposed method offers a simpler control scheme and eliminates the adverse effects caused by the self-inductance variation. A laboratory prototype is built to verify the theoretical analysis. The experimental results show that the system achieves ZVS operation and minimum reactive current within an air gap range of 20–50 mm, and efficiency reaches 91.2%.

In electric vehicle wireless power transfer (EVWPT) systems, misalignment tolerance has always been one of the concerns. This paper proposes an optimization method of EVWPT system misalignment tolerance through coupling mechanism design and circuit topology analysis. Using the mutual inductance complementary characteristics of the compensation coil and the receiving coil, and using the output series topology, the system has good misalignment tolerance performance and constant voltage (CV) output characteristics. Theoretical analysis and simulation results verify the effectiveness of the proposed method, and the system can achieve good load-independent CV output within the range of 50% misalignment.

In the rotary steering system of oil drilling, both power and data transmission are needed. This paper presents a parallel power and data transmission method for a rotating steering system with output voltage control. To reduce the size of the system, power and data are transmitted through the same rotational coupling mechanism. A power transfer resonance circuit is used to suppress the influence of the power transfer on data transmission. Therefore, crosstalk interference between the power and the data transmission channel is negligible. The experimental prototype is built, and the feasibility of the data transfer method and the closed-loop control method is verified. The experimental results are in good agreement with the theoretical analysis.

Due to the effects of splitting frequency and cross coupling, the resonant frequency of the WPT system usually deviates from the given frequency band, and the system operating at the given frequency band suffers a very low output power. Ensuring that electric vehicle wireless power transfer (EV-WPT) systems operate at a resonant state is the prerequisite for efficient energy transfer. For this purpose, a novel design method by manipulating the eigenstate parameters is proposed in this paper. The proposed system can make a EV-WPT system with arbitrary coil successfully to resonate at any given bands, not just a single band. Therefore, the method designed in this article cannot only eliminate the problem of low power caused by frequency deviation, but also realize the application requirements of multiple frequency bands. Firstly, this article establishes an accurate state space model of an n-coil fully coupled EV-WPT system, and after that, the analytical current response on each circuit is derived. Based on that, a detailed frequency spectrum analysis is presented, along with several essential spectrum parameters’ derivations, including center frequencies and bandwidths. Then, with the center frequency and bandwidth as the design indexes, a novel methodology of designing to make EV-WPT systems achieve resonant-state at arbitrary given bands is derived. Finally, simulation and experimental verification are carried out. Simulation and experimental results show that whether it is a single-band or multi-band system, the accuracy of the value under designed resonant frequency is less than 0.01, which can effectively eliminate the frequency deviation phenomenon and obtain the maximum power output at the given frequency band.

In order to solve the cross-coupling problem in the multirelay magnetic coupling wireless power transfer (MC-WPT) system, a set of magnetic cross-decoupling coil structure is designed in this paper. The coupling mechanism uses the mutual decoupling principle of bipolar coils and unipolar coils to realize the decoupling of non-adjacent coils, while the adjacent coils remain coupled. The frequency characteristics and output characteristics of the cross-decoupling dual-relay system based on the LCC-Multi-S topology are studied. It is found that the system can achieve open-loop constant voltage (CV) output, and the frequency of the optimal efficiency does not deviate from the resonance frequency point. At the same time, the proposed coil structure is compared with the traditional four-coil structure. The experimental results show that the proposed coil structure achieves cross-decoupling and better CV output, suppresses frequency drift and improves system stability.

针对一类既需多级输出又能延长传输距离的无线电能传输(WPT)场合,从磁耦合谐振基本原理出发,结合多中继结构与多负载结构的优势,设计了一种新型三线圈双负载WPT系统.该系统选用LCC-Multi-S型补偿拓扑,在传统双线圈系统中加入一级特殊的接收线圈,设计了两级接收线圈结构,推导了系统双负载恒压输出条件,实现了两级负载端的相同功率输出,同时系统WPT距离得到延长.仿真和实验验证了提出的方案的可行性.

In the dynamic wireless charging system for EVs, the cascaded multi-stage transmitting rail is widely used due to its unique advantages. Combined with the LCC-S constant voltage output compensation topology, the system control method is also simplified. However, the primary side structure of this method is pretty complicated and the number of components is large. The cost is very expensive in long-distance applications. In response to this problem, this paper proposes a method of adding a relay coil to the secondary coil. By setting the transmitting, relay and receiving coils as series compensation, the primary side structure is simplified while maintaining the dynamic constant voltage output of the system and saving the cost of components. Theoretical analysis and simulation results verify the feasibility and superiority of this method.