The scenario of multiple wireless power transfer (WPT) systems working closely, synchronously or asynchronously with phase difference often occurs in power supply for household appliances and electric vehicles in parking lots. Magnetic field leakage from the WPT systems is also varied due to unpredictable asynchronous working conditions. In this study, the magnetic field leakage from parallel WPT systems working with phase difference is predicted, and the induced electric field and specific absorption rate (SAR) in a human body standing in the vicinity are also evaluated. Computational results are compared with the restrictions prescribed in the regulations established to limit human exposure to time-varying electromagnetic fields (EMFs). The results show that the middle region between the two WPT coils is safer for the two WPT systems working in-phase, and the peripheral regions are safer around the WPT systems working anti-phase. Thin metallic plates larger than the WPT coils can shield the magnetic field leakage well, while smaller ones may worsen the situation. The orientation of the human body will influence the maximum magnitude of induced electric field and its distribution within the human body. The induced electric field centralizes in the trunk, groin, and genitals with only one exception: when the human body is standing right at the middle of the two WPT coils working in-phase, the induced electric field focuses on lower limbs. The SAR value in the lungs always seems to be greater than in other organs, while the value in the liver is minimal. Human exposure to EMFs meets the guidelines of the International Committee on Non-Ionizing Radiation Protection (ICNIRP), specifically reference levels with respect to magnetic field and basic restrictions on induced electric fields and SAR, as the charging power is lower than 3.1 kW and 55.5 kW, respectively. These results are positive with respect to the safe applications of parallel WPT systems working simultaneously.

To meet the regulations established to limit human exposure to time-varying electromagnetic fields (EMFs) such as the International Committee on Non-Ionizing Radiation Protection (ICNIRP) guidelines, thin metallic sheets are often used to shield magnetic field leakage in high power applications of wireless power transfer (WPT) systems based on magnetic field coupling. However, the metals in the vicinity of the WPT coils cause the decrease of self and mutual inductances and increase of effective series resistance; as such, the electric performance including transmission power and the efficiency of the system is affected. With the research objective of further investigating excellent shielding effectiveness associated with system performance, the utilization of the optimal magnetic field shielding method by metallic sheets in magnetic field coupling WPT is carried out in this paper. The circuit and 3D Finite Element Analysis (FEA) models are combined to predict the magnetic field distribution and electrical performance. Simulation and experiment results show that the method is very effective by obtaining the largest possible coupling coefficient of the WPT coils within the allowable range and then reducing the value nearest to and no smaller than the critical coupling coefficient via geometric unbroken metallic sheets. The optimal magnetic field shielding method which considers the system efficiency, transmission power, transmission distance, and system size is also achieved using the analytic hierarchy process (AHP). The results can benefit WPT by helping to achieve efficient energy transfer and safe use in metal shielded equipment.

For wireless charging of electric vehicles (EVs), increasing the output power level is particularly important. In this paper, the purpose of improving the output power while maintaining optimal transmission efficiency is achieved by optimizing the parameters of the compensation topology under the premise that the coupled coils of the system does not need to be redesigned. The series-series (SS) and hybrid-series-parallel (LCC, composed by an inductor and two capacitors) compensation topology are studied. The influence factors of load resistance to achieve optimal efficiency, the influence of LCC compensation parameters on the power output level, and the influence of parameter changes on system safety are analyzed. Theorical results show that by rationally designing the LCC compensation parameters, larger output power and optimal transfer efficiency can be achieved under different load resistance by adjusting the inductances of the primary and secondary compensation circuits. The output power of the optimized system with adjusted LCC compensation topology is increased by 64.2% with 89.8% transfer efficiency under 50 ohms load in experiments. The correctness and feasibility of this parameter design method are verified by both theorical and experimental results.

With the rapid development and extensive application requirements of wireless power transfer (WPT) technology, the common symmetrical WPT system is growing more mature, but it may still struggle to meet the vast demands. When the WPT system has a long transmission distance and the dimensions of transmitter and receiver coil are asymmetric, the current in the transmitter coil of traditional two-coil symmetrical structure may be excessive. The addition of a relay coil between the transmitter and the receiver coil can effectively reduce the current of transmitter coil, thereby improving system efficiency and reducing electromagnetic field (EMF) leakage. In this article, the parameters of relay coil are optimized by theoretical calculation and multiobjective genetic algorithm. The results show that the optimized three-coil system can reduce the current of transmitter coil by 73.1%, improve the efficiency by 10.7%, and suppress the EMF leakage by 12 dB simultaneously. Finally, the effectiveness of the proposed system is verified by experiments.

In order to improve the transmission performance of the wireless power transfer (WPT) system under misaligned conditions, a novel type of dual-channel DDP type transmitter coil is proposed inspired by the traditional LCC compensation circuit and DD coil. The proposed DDP coil is a combination of DD coil and P coil, which jointly establishes the main flux for magnetic coupling and power transmission. At the same time, the P coil also acts as the resonant inductor of the LCC compensation circuit of the WPT system. When the system parameters are well designed, we can achieve relatively more stable output current during the offset of the primary and secondary sides. Experimental results indicate that when the misalignment varies from 0 m to 0.15 m, the output current variation range is 2.92 A to 3.68 A, the current fluctuation rate is 11.5%. Compared with the traditional DD coil with LCC topology, the proposed dual-channel transmitter DDP coil shows better performance in misalignment tolerance.

Wireless power transfer via strongly coupled magnetic resonance is an effective and convenient technology to transfer energy. The output power splitting in close distances and monotonic decay of the output power in longer distances exist when it comes to single‐transmitter case. For the sake of more stable output power in a broader space, the authors proposed a novel wireless power system with multiple transmitters. Further analysis of features of both single‐transmitter and multiple‐transmitter systems was presented with the adoption of MATLAB and High‐Frequency Structure Simulator. The authors demonstrated the superiority of the multiple‐transmitter system and then investigated the impact of transmitter spacing on output power. To stabilise the output power as much as possible, an optimisation strategy is designed by setting transmitter spacing as decision variables and the minimum power variance as the target. The measurement shows that for a load demand of 5 W, a stable area with a standard deviation of 0.32 can be achieved when transmitters are placed 0.33 m apart. Both theoretical and simulation results make it possible to power the movable devices more stably.