Multi-coil high efficiency wireless power transfer system against misalignment

It is well known that the power transfer efficiency (PTE) of a two-coil wireless power transfer (WPT) system is maximized at critical coupling under fixed system parameters. However, the two-coil WPT system is critical-coupled with a relatively short distance between the coils. To overcome the problem, a multicoil WPT system has been studied. In this paper, we review the impedance characteristics of the critical-coupled two-coil WPT system and reveal that the conventional three-coil WPT system cannot have the same impedance characteristics as critical coupling. Based on the impedance matching conditions with critical coupling of the two-coil WPT system, we propose a design method of a three-coil WPT system in which the free resonant frequencies of all resonators are changed. The proposed design method is successfully implemented at the operating frequency of 6.78 MHz. The experimental results are in good agreement with the simulated PTEs and show that by changing the free resonant frequencies, a higher PTE can be effectively achieved in comparison to the conventional two-coil and thee-coil WPT systems.

This article is the continuation of graph sets method (GSM) proposed in the companion paper Part I for deriving equations and analyzing multicoil wireless power transfer multicoil (MC) wireless power transfer (WPT) systems. After explaining GSM, categorizing WPT coils into three different types, and proposing some approximation techniques in Part I, this article, as the second part of this work, presents numerical simulations and experimental results for a three-coil MCWPT system similar to what is explained in Part I. The simulations are conducted in MATLAB/Simulink and ANSYS environments, and for the experimental model, three ferriteless cylindrical coils are built and compensated to behave as voltage driven, current driven, and passive coils, respectively, at the specific frequency of 200 kHz. After analyzing and comparing the simulation and experimental results, it is shown that GSM can be an effective and illustrative technique that facilitates comprehensive analysis of interactions amongst the coils and their characteristics, especially when WPT systems contain multiple coils.

In previous researches, an operator-based sliding mode control design to achieve high power transfer efficiency of a wireless power transfer (WPT) system via magnetic resonance coupling were shown. However, it is difficult to reduce the steady-state error by using SMC-based tracking controller. In this paper, an operator-based integral sliding mode control method is adopted to reduce the steady-state error in the WPT system. Moreover, high power efficiency should be achieved in the WPT system by using an impedance matching control. The effectiveness of the proposed method is verified by simulation results.

Achieving high stable Power Transfer Efficiency (PTE) in Wireless Power Transfer (WPT) systems remains challenging due to the nonlinear, multimodal nature of the optimization space. Conventional algorithms such as Genetic Algorithms (GA), Differential Evolution (DE), and Simulated Annealing (SA) often face premature convergence, sensitivity to parameter settings, and inconsistent performance across runs. To overcome these issues, this study introduces the Evolutionary-Swarm Hybrid Algorithm (ESHA), which integrates DE for directional exploration, GA crossover for population diversity, SA for adaptive convergence, and Lévy Flights for stochastic global search. ESHA was implemented on a WPT system with a fixed 20 cm transmission distance and compared with GA, DE, and SA using three performance indicators: PTE, convergence speed, and computational efficiency. Results show that ESHA achieved a maximum PTE of 97.18%, surpassing GA (96.81%), DE (96.65%), and SA (96.19%), while maintaining zero variance across independent runs. It converged in an average of 31.2 iterations, slightly faster than GA (33.15) and SA (32.1), and comparable to DE (31.3). Execution time was 0.4738 s, close to GA (0.4654 s) and only marginally higher than DE (0.4262 s) and SA (0.4329 s). Statistical validation confirmed significant improvements in PTE (p < 0.05).

A highly efficient wireless power transfer (WPT) system is required in many applications to replace the conventional wired system. The high temperature superconducting (HTS) wires are examined in a WPT system to increase the power-transfer efficiency (PTE) as compared with the conventional copper/Litz conductor. The HTS conductors are naturally can produce higher amount of magnetic field with high induced voltage to the receiving coil. Moreover, the WPT systems are prone to misalignment, which can cause sudden variation in the induced voltage and lead to rapid damage of the resonant capacitors connected in the circuit. Hence, the protection or elimination of resonant capacitor is required to increase the longevity of WPT system, but both the adoptions will operate the system in nonresonance mode. The absence of resonance phenomena in the WPT system will drastically reduce the PTE and correspondingly the future commercialization. This paper proposes an open bifilar spiral coils based self-resonant WPT method without using resonant capacitors at both the sides. The mathematical modeling and circuit simulation of the proposed system is performed by designing the transmitter coil using HTS wire and the receiver with copper coil. The three-dimensional modeling and finite element simulation of the proposed system is performed to analyze the current density at different coupling distances between the coil. Furthermore, the experimental results show the PTE of 49.8% under critical coupling with the resonant frequency of 25 kHz.

The wireless power transfer (WPT) system based on parity-time (PT) symmetry has the advantages of robustness, stable, and efficient power transmission. However, the region of PT symmetry is limited, which cannot satisfy some practical requirements. Multiple transmitting coils have been shown to improve the misalignment tolerance of WPT systems. Towards this end, a parity-time-symmetric-based WPT (PT-based WPT) system with double-transmitting coil is presented in this article. First, an approximate equivalent circuit model of this PT-based WPT system was developed. Second, compared with the conventional single transmitting coil PT-based WPT system, the proposed system expands the PT symmetry region and provides higher output power and transmission efficiency. Furthermore, the mutual inductance between two transmitting coils can be designed to meet the requirements of different scenarios, which improves the freedom of system design. Finally, a 30 W prototype is designed to evaluate the proposed WPT system. Experimental results show that the critical coupling coefficient is reduced by about 12.5% at <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sub> = 0.51, which implies a longer transmission distance. Moreover, the maximum output voltage fluctuation in the strongly coupled region is only 3.5%, while the transfer efficiency is approximately constant, which implies stable and efficient power transfer.

This paper proposes double C-shaped reactive shielding coils to alleviate the efficiency degradation caused by the reactive shielding method. Using the proposed method, higher power transfer efficiency and EMF shielding performance than the conventional reactive shielding coil can be achieved. The main idea of the proposed shielding coils is to create an additional inner loop by making the shielding coil into two C-shaped loops. In the inner loop of the proposed shielding coils, current flows in the same direction as that of transmitting coil to amplify the magnetic field. In the outer loop, current flows in the opposite direction to cancel the leakage magnetic field. In this paper, the wireless power transfer system with the proposed shielding coils is designed and verified through 3D electromagnetic and circuit simulation.

Simultaneous power distribution to multiple loads using a single source in the wireless power transfer (WPT) system is a challenging issue due to cross-coupling between the load coils, which reduces the power transfer efficiency. In a resonant WPT system, when two or more coils operated under over coupled condition, the original operating resonant frequency gets bifurcated, and thereby reduction in the power transfer efficiency. Different techniques are investigated in the literature to mitigate the frequency bifurcation phenomena in the resonant WPT system. However, the utilization of frequency bifurcation approach for the simultaneous power transfer to multiple loads is not addressed. This paper proposes a simultaneous power transfer approach using frequency bifurcation for the multiple load system designed with different operating frequency. Mathematical, simulation, and experimental studies performed for dual, triple, and four coil WPT systems with multiple loads. In addition, an automatic power flow control method is implemented to estimate the load current from the source, which helps to select a new set of load coils to be charged. The experimental results confirm the proposed power transfer, helps to attain higher power transfer efficiency of 39.34%, 49.31%, 68.22% and cross interference of -31.2 dBV, -36.2 dBV, -41.2 dBV for dual, triple, and four coil WPT system, respectively.

Many researches have been carried out by previous researchers to get better performance of a wireless power transfer (WPT) system. This research uses a partitioned shielding made of metallic material to protect WPT system from electromagnetic interference (EMI). Also, a shielding material is connected to ground, so that it can reduce occurrence of stray/parasitic capacitance between electrodes of electronic components. Both the electromagnetic interference and the stray/parasitic capacitance can deteriorate performance of WPT system. In this research, the WPT system works at voltage 14.7V, frequency 56,298 Hz, distance coil to coil is 0 till 5 cm. The efficiency of WPT system is achieved until 14.9 % (without shielding) and until 17.9% (with partitioned shielding).

In this paper, a new approach is proposed to achieve maximum coupling coefficient for the windings in circular Wireless Power Transfer (WPT) systems. The designed magnetic structure has the maximum magnetic coupling coefficient in a specific air gap in order to maximize the system efficiency. Series resonant compensator network is analyzed in frequency domain and proper operating point is selected to achieve constant voltage gain in different loads. This system controls output voltage through a closed loop control via controlling inverter's duty cycle. The design procedure is explained for a 5 kW system. This system can transfer power from 100mm to 200mm air gap by resonant network and magnetic circular coupling that has a 480mm diameter. Efficiency results for output power in various air gaps are presented, where efficiency of the nominal load for 150mm air gap is 93%.

An energy-efficient high-powermulti-coil wireless power transfer system (WPT) has been studied in this paper. The proposed system was first analyzed and examined using theoretical modeling; this was followed by finite element analysis and circuit simulation to confirm the goal. As the air gap between the transmitter and receiver coils widens, the coupling coefficient of a WPT system will drop. A large-air-gap WPT system’s coupling coefficient can be raised by adding relay coils between the transmitting and receiving coils. On the other hand, an increased coupling coefficient improves the system’s overall power transfer efficiency. The suggested multi-coil system, which has an air gap of 15 cm and a lateral misalignment of 3 cm between the transmitting and receiving coils, has been simulated and verified using the Maxwell 3-D finite element tool and Ansys Simplorer circuit simulation software.

In this paper, we propose an efficient wireless power transfer (WPT) system at 1050 kHz for an active capsule endoscope. The performance of the proposed WPT system is evaluated by placing a capsule receive coil in a hollow body phantom as well as that filled with colon-equivalent liquid. The power transfer efficiency has been studied with respect to the operating frequency and the load resistance. The measured results show that the maximum power transfer efficiency of 20.4% and 17.47% can be achieved in a hollow and a liquid phantom, respectively.

In this paper, we propose a method to reduce the leakage magnetic field from wireless power transfer (WPT) systems with series–series compensation topology by adjusting the phase difference between the transmitter (TX) coil current and the receiver (RX) coil current without additional shielding coils or materials. A WPT system employing the proposed method adjusts the phase difference between the TX coil current and RX coil current by tuning a resonant capacitor of the RX coil. The conditions for minimizing the leakage magnetic field are derived, and the range of the resonant capacitor of RX, considering power transfer efficiency and the leakage magnetic field, is proposed. Through simulations and experiments, it is verified that the proposed method can reduce the leakage magnetic field level without any additional materials. For that reason, the proposed method can be suitable for size-limited, weight-limited or cost-limited WPT systems.

In this article, we propose a compact module‐integrated wireless power transfer (WPT) system for miniaturizing a WPT system and improving power transfer efficiency (PTE) within the operating distance. Using an eddy current (and its associated magnetic field) formed in a module‐integrated square metal plate, the proposed WPT system realizes a uniform mutual inductance between the coils within the operating distance and achieves an improved PTE of up to 54.7% at 6.78 MHz compared to the conventional WPT system.

The use of resonant magneto-inductive links is an efficient technique to transfer power over midranges in the field of wireless power transfer (WPT). Power transfer efficiency (PTE) and power delivered to the load (PDL) are two important indicators of power transmission for a WPT system. A predetermined amount of PDL need be generated at maximum PTE for practical application in a WPT system; thus, the authors focus on maximising PTE and a predetermined amount of PDL for transfer in this study. First, load-matching conditions are presented for maximum PTE transfer though circuit theory-based analyses. Then, a new tuning method is proposed to transfer a predetermined amount of PDL which can be controlled by source-matching distance at maximum PTE. The relations between the loss of a load-matching resonator and the PTE (or PDL) of a correspondingly unmatched system are derived though analyses as well. Finally, the calculated results of the design examples are verified through electromagnetic simulations and experimental measurements.