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The prosperity of market in multi‐charging devices has made the researches on multi‐load magnetically coupled resonant (MCR) wireless power transfer (WPT) technique be an urgent issue nowadays. For the sake of load recognition and controllable power distribution, the concept of multi‐frequency excitation was introduced into multi‐load MCR WPT systems. However, the transferred power components at different frequencies inevitably suffer the cross interference at receivers, which negatively affects the accuracy of load recognition and power distribution. To suppress the cross interference, a methodology by using the metamaterial composed of a printed circuit board (PCB) spiral inductor and a lumped capacitor was proposed. The concept of equivalent mutual inductance (Meq) was presented to quantitatively describe the influence of metamaterials on the couplings between the transmitting (Tx) and receiving (Rx) coils. By magnetic field simulation, a series of Meq curves versus operating frequency under different metamaterial parameters were plotted and an optimal design was adopted to suppress the power components at non‐targeted frequencies. Moreover, a detailed circuit model was built to characterize the output power of multiple loads after introducing the metamaterial. Finally, the experiments from a prototype was carried out and the experimental results verified the effectiveness of proposed suppression methodology.

With urgent market demand for multiload electronic applications, multiload magnetically coupled resonant (MCR) wireless power transfer (WPT) system has caused widespread concern. In the practical applications, multiload MCR WPT system should have the capability to realize targeted power distribution among loads and stable output power against misalignment of load. To achieve this goal, a multiphase multifrequency system with multiple loads is proposed in this article, where multi-phase structure of transmitting coils can enhance the misalignment tolerance, and multiple operating frequencies are beneficial to achieve multiload identification and targeted power distribution. For simplicity, this article mainly studies a two-phase dual-frequency system with two loads and proposes two phase-shifted control strategies. The equivalent circuit model of the system is established, and the output power in the open-loop system under two phase-shifted control methodologies are analyzed. According to that, the targeted power distribution strategy by adjusting the resonant frequency of the transmitter is implemented. Moreover, the closed-loop control schemes based on phase-shifted control methodologies are adopted to realize stable output power precisely against the misalignment of loads. Finally, a prototype of two-phase dual-frequency MCR WPT system with two loads is built in the laboratory. The experimental results prove the correctness of the theoretical analysis.

Multi-phase magnetically coupled resonant (MCR) wireless power transfer (WPT) technology can fulfill the requirements of time-varying spatial positions of loads in mid-range applications, as it can generate a rotating magnetic field around sending coils, and effectively reduce the limits of spatial positions on transfer characteristics including output power and transfer efficiency. Nevertheless, the design of coils parameters and control strategies put a great influence on the realistic transfer characteristics, which should be considered elaborately in practice. In this paper, a three-phase MCR WPT system with cylinder-shaped coils is investigated, the equivalent circuit model is built to carry out the theoretical analysis. Based on that, the influence on zero-voltage-switching (ZVS) conditions of power switches and the output power of the system, resulting from different phase-shifted angles between each phase, coil turns and angular misalignments of the receiving coil, is analyzed comprehensively. Detailed discussions on relationships among coil turns, the angular misalignment, ZVS conditions, and the output power are completed under different phase-shifted angles. Furthermore, the parametric optimization of coil turns, as well as phase-shifted angles, are proposed to ensure the power switches realize ZVS and ensure the system realize stable output power within the full range of angular misalignment. Finally, experiments are carried out to evaluate the accuracy of theoretical analysis and confirm the validity of the proposed optimal design.

Multi-module series-parallel (MMSP) power systems have the superiority of easy scalability and high reliability, and is the prospective candidate for high-power conversion. In this paper, the MMSP configuration is implemented in wireless power transfer (WPT) applications. However, the voltage and current sharing issues have not been analyzed precisely in existing researches. To obtain the inherent principle of voltage and current sharing in the MMSP WPT system, the dual-module series-parallel WPT systems with four configurations are studied as examples. By the fundamental harmonic analysis, the characteristics of a WPT module are obtained, and then the imbalance mechanism of voltage and current under four kinds of parameters mismatches are revealed. The results of circuit simulation verify the correctness of the theoretical analysis.

High-power magnetically coupled resonant (MCR) bidirectional wireless power transfer (BWPT) within long distance can be potentially used in various applications. However, the coupling between transmission coils will drastically decrease with the rise of distance to diameter (d-D) ratio, and voltage/current stresses on resonant components tend to increase apparently, which further deteriorate the system efficiency and stability. In this paper, the relationship between the coupling coefficient and the d-D ratio in high-power BWPT systems is analyzed by mathematics methods. The correlations of transferred power and system efficiency with d-D ratio are presented consequently. The scheme of coils magnetic concentration and double-layer coils in parallel is adopted to improve the system performance. The theoretical analysis is demonstrated by the experimental results of a 2kW prototype, and the system efficiency is improved from 70.7% to 77.47% under the d-D ratio of 1 (300mm-300mm).

For multi-source and multi-load wireless power transfer (WPT) applications, a novel architecture of modular stacked multi-port wireless energy interconnection system (WEIS) with virtual AC bus is presented in this paper, which has following advantages: 1) it can serve as the interface among multiple sources and multiple loads; 2) bipolar coils are applied to eliminate the cross-coupling among multiple coils; 3) the relay coils with constant current characteristics are adopted as a virtual AC bus, and the system power distribution is greatly simplified by the proposed phase-shifted control method; 4) the modularization of power converters, coils and compensation networks greatly enhances the system applicability and scalability. A four-port WEIS prototype with the rated power of 2kW was built, and experiments were carried out for typical operation modes including single-source three-load mode and dual-source dual-load mode, which verified the effectiveness of the proposed system architecture.

Nowadays, the magnetically coupled resonant (MCR) wireless power transfer (WPT) system are mostly the single-source or single-load systems that operate at “one to one” mode. With the increasing number of electrical equipment and types of input sources, the “one to one” mode cannot meet the application requirements. Therefore, the "one-to-many" and "many-to-many" WPT become increasingly important. In this paper, a three-port MCR wireless energy router (Wi E-Router) architecture with dual sources and dual loads is investigated in detail, which allows power transfer among dual sources and dual loads wirelessly. The equivalent circuit model of the system is built to analyze its transfer characteristics. Moreover, an effective power management strategy for a variety of input power cases is proposed. Finally, the theoretical analysis is validated by the experimental results from a 600 W prototype.

In multi-frequency multi-load magnetically coupled resonant wireless power transfer (MCR WPT) system, multiple inverters are usually employed to respectively provide a single frequency excitation voltage, and then a multi-frequency excitation voltage can be obtained through superposition methodology. However, the system still has the limitation due to complicated architecture and bulky volume. In this paper, only one single-phase full-bridge inverter is adopted in multi-load MCR WPT system, and a multi-frequency pulse width modulation (MFPWM) control strategy is proposed to integrate multiple frequency components into the single-phase inverter. In view of different excitation voltage characteristics, the unipolar and bipolar strategies are proposed respectively, along with the corresponding algorithm. The differences between the two control strategies in the modulation ratio range and harmonic content are discussed in detail. Finally, a hardware platform is built for experimental verification.

Magnetically coupled resonant (MCR) wireless power transfer (WPT) is capable of supplying power to multiple loads simultaneously. To realize load identification and efficient power distribution in multi-load MCR WPT system, a multi-frequency driving method was implemented. However, this methodology allows loads to receive power at different frequencies, leading to a cross interference among multiple loads and deteriorating the power distribution accuracy. In this paper, a double-frequency double-load MCR WPT system was investigated as an example. To suppress the cross interference in the system, a printed circuit board (PCB) type metamaterial slab was designed to reduce the equivalent mutual inductance between transmitter (Tx) and receiver (Rx) coils at non-targeted frequencies, blocking the transfer channel of non-targeted power components. The suppression effect to cross interference was confirmed by the experiment results.

Recently, LCCL-LC compensated magnetically coupling resonant wireless power transfer (MCR WPT) systems are widely used to achieve the constant and load independent output voltage performance compared with other counterparts. To analyze the zero-voltage-switching (ZVS) conditions of the system, the fundamental harmonic approximation (FHA) model is usually utilized, but the analytical results are not accurate due to the neglect of high order harmonics. In this paper, a time domain model considering high order harmonics was proposed to solve this issue. Based on that, a method of modulating the compensated capacitor was put forward to realize ZVS within the full range of loads. However, this method will cause the system to deviate from its full resonance state and further deteriorate the system efficiency. To enable the system to realize ZVS in the full resonance state, the improved optimization method to modulate the compensated inductor was proposed. Finally, a 1kW prototype was built and a series of experiments were carried out, the experimental results demonstrate the effectiveness of the parameters optimization for ZVS realization. The overall efficiency enhancements by the two proposed methods are 0.47% and 1.31% respectively.

In medium-to-high power magnetically coupling resonant wireless power transfer (MCR WPT) systems, either voltage stress or current stress on resonant components tends to be an important issue, depending on the input and output specifications. High current stress will increase the conduction loss on coils and reduce the efficiency, while high voltage stress will bring the difficulty to the design of resonant components and also will deteriorate the system reliability. In this paper, a parameter design methodology based on voltage/current stress optimization is proposed for LCCL-LC compensated MCR WPT systems. By designing the resonant frequency and the self-inductance of two coils properly, the voltage/current stress of the components are effectively controlled. A 1kW LCCL-LC compensated MCR WPT system is built, the trade-off of voltage/current stress among all the resonant components was obtained, and the high efficiency up to 92.2% is also achieved.

Nowadays, bidirectional wireless power transfer (BWPT) technology has caused increasingly concern, but its application is greatly limited when the number of sources and loads increases. In this paper, the concept of multi-port wireless energy router (Wi E-Router) is proposed to realize energy transfer wirelessly among multiple sources and loads for the multi-source and multi-load wireless power transfer (WPT) applications. Specifically, a three-port magnetically coupling resonant (MCR) Wi E-Router with LCC hybrid compensation network is investigated in detail. The equivalent circuit model of the three-port Wi E-Router is built and the power transfer characteristics are analyzed. Based on the circuit model, the relationships between the power magnitude as well as flowing direction and the shifted phase among or inside multiple ports are revealed. Moreover, a zero-power-flow control scheme is put forward for the case when one port quits from the system. By regulating the outer shifted phase, the power transfer among other ports can still be realized when the idling port achieves zero power flow. Finally, the validity of the above theoretical analysis is verified by experiments.

Magnetically coupled resonant (MCR) wireless power transfer (WPT) is one of the most promising WPT technologies for its remarkable capability of simultaneous noncontact power transfer for multiple independent loads. Nevertheless, diverse energy requirements of different loads and efficiency quota make it difficult to design and optimize the multiload system. In this paper, a novel driver configuration for the MCR WPT system with multiple loads is proposed, in which the transmitting resonant tank is driven synchronously by multiple inverters operating at multiple switching frequency and sharing a common dc voltage source, then a multifrequency superposition methodology is presented to achieve high efficiency and targeted power distribution. The dominant features of the methodology are listed as follows: 1) the multifrequency power components from multiple inverters can be simultaneously delivered to multiple loads through a single transmitter; 2) the receiving coils are elaborately designed at different resonant frequencies that correspond to the operating frequencies of multiple inverters to achieve targeted power transfer and high efficiency; 3) the resonant frequency of the transmitter can be modulated within the adjacent area of multiple operating frequencies, and the power distribution to meet the requirements of selective loads will be realized; and 4) the resonant frequencies of receivers can also be adjusted to effectively realize the power distribution. In this paper, a double-frequency MCR WPT system with two loads is comprehensively investigated as a representative example, and the studied methodology has been experimentally verified by two prototypes of the proposed circuit configurations.

Simultaneous non-contact energy transmission for multiple loads with separate receiving coils is a remarkable advantage of magnetically coupled resonant (MCR) wireless power transfer (WPT). A novel multi-frequency driver configuration for MCR WPT system with multiple loads is proposed, where the receiving resonant tanks are severally tuned at different resonant frequencies to make the loads selective. A methodology of adjusting the resonant frequency of the transmitter is presented to satisfy diverse energy requirements of specific loads. However, the cross interference from non-targeted frequencies inherently exerts an influence between multiple receivers, and thus makes power allocation non-constrained through multi-coupling channels, which increase the difficulty of power control and parameters design. In order to reduce and further eliminate the influences of the cross interference and realise targeted power distribution for selective loads, three types of parallel and series resonant compensation circuits are introduced into receivers. By flexibly utilising the impedance characteristics of parallel and series resonant networks, the proposed compensation circuits are proved to be effective, significantly reducing the cross interference and exclusively delivering power to the selective loads corresponding to pre-tuned resonant frequencies. Finally, the experimental results from a prototype have confirmed the effectiveness of the proposed methods.

Previous work reveals that the magnetically coupled resonant (MCR) wireless power transfer (WPT) technology is efficient and practical for mid-range wireless energy transmission, able to handle nontrivial amount of power. This paper presented an equivalent analytical model for MCR WPT system to incorporate spatial misalignments between the transmitting coils and receiving coils. The mutual inductance formulas were derived when receiving coils are laterally, angularly or generally misaligned from transmitting coils. The relationship among the output power, transmission efficiency and the mutual inductance, load resistance were analyzed in detail. Experiments had also been carried out to facilitate quantitative comparison and validate the theoretical analysis.

Multi-load wireless power transfer (WPT) using electromagnetic induction principle has attracted increasing attention recently. However, there is much difficulty to achieve targeted power distribution to multiple loads and stable transmission power with misalignment between sending coils and receiving coils. To solve this problem, as a representative case, this paper employs a two-phase magnetically coupled resonant (MCR) WPT system with two receiving coils. The receiving coils are adjusted at two different frequencies to implement load identification. Meanwhile, by adjusting the resonant frequency of sending coils, the targeted power distribution to selective loads is achieved. Furthermore, the system combines two orthogonal sending coils excited by two equivalent ac sources with phase-shifted angle control to stabilize the transmission power. Finally, a prototype is built to test the transmission power of the system and the experimental results are in agree with the theoretical analysis.

In multi-load magnetically coupled resonant (MCR) wireless power transfer (WPT) systems, it is an urgent issue to satisfy the power requirement of loads with high efficiency. In this paper, a multi-frequency concept is introduced to solve this issue. By employing the coil structure with a single transmitter and two receivers, a double-frequency circuit configuration driven by two inverters is implemented to transfer power to loads. Based on the influential factors on transmission characteristics revealed from the equivalent circuit model, a high efficiency design method and a power distribution control strategy are put forward respectively. Finally, a prototype of the double-frequency double-load MCR WPT system is built in the laboratory and the experimental results have shown the validity of the proposed high efficiency design and power distribution control methods.

Multi-load magnetically coupled resonant (MCR) wireless power transfer (WPT) system has attracted more attention recently due to its long-distance power delivering and simultaneous power supply for different electrical loads. However, the spatial misalignments between sending and receiving coils will exert an influence on the transmission characteristics of system owing to time-varying mutual coupling between coils. Taking a double-load system for example, this paper investigates an equivalent circuit model of the double-cheeked MCR WPT system under different spatial misalignments between the sending coil and two receiving coils. Based on fundamental harmonic analysis and equivalent circuit theory, the influence of spatial scales on the transmission power and transmission efficiency is analyzed in detail. The mutual inductance between the sending coil and the receiving coil in the general case is calculated to find out the tendency of the transmission characteristics of the system under different spatial scales. The experiments of the double-cheeked MCR WPT system with two receivers are carried out and the results agree with the theoretical analysis well.

Wireless power transfer (WPT) that is essentially based on electromagnetic induction has been attracted increasing attention recently. Most of the previous work revealed that the transfer characteristics of the system would be greatly influenced by the spatial positions between the sending coils and the receiving coils. This paper focuses on a two-phase magnetically coupled resonant (MCR) WPT system, which incorporates two orthogonal sending coils excited by two equivalent ac sources with phase-shift angle control and a single receiving coil, and investigates the distribution of magnetic field around the sending coils under different angular misalignment of the receiving coil. The calculation of the magnitude of magnetic field, the induced voltage, and the output power are given in detail, along with the simulation verification by Maxwell. Finally, a prototype is built and tested to verify the theoretical analysis.

Multi-phase magnetically coupled resonant (MCR) wireless power transfer (WPT) technology, which can effectively reduce the limits of coils spatial locations on power transfer, has become one of the most promising technologies in the mid-range applications. In this paper, a three-phase MCR WPT system was investigated and the equivalent circuit model was built and simplified. Based on the theoretical analysis of the simplified model, the influential factors on output power of the system were revealed, including the phase-shifted angle between each phase, coil turns and spatial locations of receiving coil. Further, coil turns and control strategy of the phase-shifted angle were optimized to ensure the system realize the optimal output power characteristics that was defined as the one with high amplitude and minor fluctuations within the full range of angular misalignment. Finally, the experiments had been carried out to confirm the theoretical analysis.

Simultaneous non-contact energy transmission for multiple loads with separate receiving coils is a remarkable advantage of magnetically coupled resonant (MCR) wireless power transfer (WPT). Nevertheless, diverse energy requirements of different loads and efficiency quota make it considerably difficult to design and optimize the parameters of present single-frequency system. In this paper, a novel driver configuration for MCR WPT system with two receivers is proposed, in which, the transmitting resonant tank is driven synchronously by two half-bridge inverters operating at different switching frequencies and sharing a common dc voltage source. Then, a methodology is presented to achieve high efficiency and oriented power distribution. The dominant features of the methodology are listed as follows: 1) the receiving resonant tanks are elaborately tuned at two operating frequencies for high efficiency; 2) by adjusting the resonant frequency of the transmitter in the neighborhood of two operating frequencies, power distribution can be determined to meet the demands of specific loads; 3) the adjustment of resonant frequencies of receivers can also realize the power distribution effectively. The proposed methodology based on the new circuit configuration has been practically verified in an experimental prototype.

In a magnetically coupled resonant (MCR) wireless power transfer (WPT) system, adding repeating coils is an effective way to lengthen transmission distance and improve the transferred power in a wide range. This paper investigated a 3-coil MCR WPT system. Based on fundamental harmonic analysis on the equivalent circuit model, the relationship between the transmission characteristics and the spatial misalignments of coils were derived in detail. To improve the robustness of the output power to the spatial scales, one can adjust the position of the repeating coil to ensure the mutual inductances between sending and repeating coils, receiving and repeating coils be proportional when the spatial scales of load coil varies. To verify the theoretical analysis, a prototype of the 3-coil MCR WPT system was built and the experimental validation were carried out.

Variation of spatial scales and load resistances have significant effects on the transmission power of magnetically coupled resonant (MCR) wireless power transfer (WPT) system. To realize maximum power transmission under arbitrary spatial scale and different load resistances, a control scheme for automatic maximum power point tracking (MPPT) operation was presented in this paper. Based on the transmission power characteristics of a two-coil WPT system with a series resonant topology, a SEPIC converter was introduced to cascade at the receiving side to achieve MPPT for MCR WPT system. Adopting perturbation and observation (P&O) method to adjust equivalent input resistance of SEPIC converter dynamically, the proposed scheme tracked the maximum transmission power operating point by matching the corresponding mutual inductance with varying spatial scales. The experimental results had shown the validity of the theoretical analysis and the feasibility of the proposed scheme.

Multi-phase magnetically coupled resonant (MCR) wireless power transfer (WPT) technology has attracted wide spread attention recently, for it can not only reduce the sensitivity of system to the spatial scale effectively, but also maintain the high transmission efficiency and power in the middle distance. This paper presented an analytical equivalent model for a three-phase MCR WPT system under phase angle control method with different spatial locations between the sending coils and receiving coil. The mutual inductance formulas of the sending coils and receiving coil were derived. The relationship among the output power, transmission efficiency and the angular misalignments were analyzed in detail. Experiments have also been carried out to facilitate quantitative comparison and validate the theoretical analysis.

As a mid-range wireless power transfer (WPT) technology, magnetically coupled resonant (MCR) WPT has become a reseach focus in recent years. In this paper, an equivalent circuit model of 4-coil MCR WPT system was presented, along with the formulas of the output power and transmission efficiency. Besides, to comfirm whether spatial misalignments will influence the transmission characteristics of the system, the relationship between the mutual inductance and the spatial misalignments of the coils was analyzed, and the transmission characteristics under various spatial scales was revealed. An experiment circuit was designed and experimental results were well consistent with the theoretical analysis.

Magnetically coupled resonant (MCR) wireless power transfer (WPT) technology is efficient and practical for mid-range wireless energy transmission. For the design of MCR WPT system, it is necessary to seek optimal transmission performance under different applications. This paper presented an equivalent analytical model for such system to incorporate spatial misalignments between the transmitting coils and receiving coils. According to the obtained model, the relationship among the output power, spatial misalignments and coil parameters were analyzed in detail. To achieve maximum output power and high stability of power transfer in a specific misalignments range, a normalization method was introduced, providing critical insight into the optimal design of coils. Relative design considerations and optimization procedures were further stated. Experiments had also been carried out to evaluate the accuracy of theoretical analysis and confirm the validity of the proposed method.