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Traditional wireless power transfer (WPT) systems usually adopt the triple-phase-shift control method to maintain a constant output voltage, track the maximum system efficiency point (MEPT), and achieve zero-voltage-switching (ZVS) operation for various applications. However, these three targets are achieved at the cost of high reactive power on both primary and secondary sides, especially under light-load conditions, leading to low efficiency. This has become one of the challenges that hinder a further deployment of WPT technologies in practice. To address this vital problem, in this article, how the reactive power lowers the system efficiency is revealed based on a mathematical model established. Then, a hybrid modulation control strategy based on a proper selection between the full-bridge and half-bridge modes of the inverter and active rectifier is developed. An experimental prototype is constructed to verify the effectiveness of the proposed control method. Experimental results show that the proposed method can reduce the reactive power, maintain a constant output voltage, and realize the MEPT and ZVS operation, with high efficiencies up to 94.29% in a wide load range. [ABSTRACT FROM AUTHOR]

Efficiency remains a key challenge in wireless charging in academia and industry. In this article, a new wireless power transfer (WPT) system based on a double-half-bridge (DHB) inverter with two variable inductors (VIs) is proposed. Compared with conventional full-bridge (FB) inverters, the DHB inverter can reduce the current through the mosfets under the same output power and thus, reduce the conduction loss. Next, by adjusting the inductances of the VIs instead of using phase shift (PS) method, the output voltage or current can be controlled, while the circulating current can be eliminated and wide-range zero voltage switching operation can be achieved. Consequently, the power loss can be further reduced. Circuit analysis, VI design, as well as hardware implementation, are provided in detail. A laboratory prototype is built to verify the feasibility of the proposed method. Close agreement is obtained between simulation and experimental results. The maximum efficiency can reach 92.4%, which is 3.65% higher than traditional PS control. [ABSTRACT FROM AUTHOR]

In this article, a special magnetic coupler for three-coil wireless power transfer (WPT) is proposed to eliminate the mutual inductance between the source coil and the receiver coil, which can significantly improve the design freedom. Specifically, unipolar Q coil, mixed QDD coil, and bipolar DD coil are designed for the source coil, the transmitter coil ($\text{T}_{\mathrm {X}}$), and the receiver coil ($\text{R}_{\mathrm {X}}$), respectively. By making use of unipolar coils and bipolar coils, this structure magnetically decouples the receiver coil from the source coil. Meanwhile, under different lateral misalignment conditions, this new coupler facilitates maintaining high efficiency. A laboratory prototype has been constructed to validate the proposed structure, demonstrating that the proposed structure can realize inherent characteristics, enhance misalignment tolerance, and energy transfer. The potential applications are EV systems, but this design can be generalizable to other three-coil systems. [ABSTRACT FROM AUTHOR]

To maintain a stable output voltage under various operating conditions without introducing extra dc/dc converters, phase-shift (PS) control is usually adopted for wireless power transfer (WPT) systems. By using this method, however, zero-voltage switching (ZVS) operation cannot be guaranteed, especially in light-load conditions. To achieve high efficiency and reduce electromagnetic interference, it is significant for WPT systems to achieve ZVS operation of all switching devices in the whole operation range. In this article, an auxiliary variable inductor, of which the equivalent inductance can be controlled by adjusting the dc current in its auxiliary winding, is designed for series–series-compensated WPT systems under PS control to mitigate the loss arising from hard switching. As a result, a wide ZVS operation range of all switching devices can be achieved. A laboratory prototype is built to verify the theoretical analysis. The experimental results show that, under load and magnetic coupling variations, ZVS operation at fixed operation frequency as well as a constant dc output voltage can be maintained. Compared to the conventional method with only PS control, the proposed WPT can achieve higher overall efficiency in a wider load range owing to the wide ZVS operation range. [ABSTRACT FROM AUTHOR]

Current imbalance in multistring light-emitting diodes (LEDs) is a critical issue. It may cause overcurrent in one or more LED strings, leading to rapid degradation. In this paper, a mixed high-order compensation networks-based wireless power transfer system is proposed to generate multiple constant current outputs. It is composed of an LCC resonant network in the transmitting side, a series resonant network, and multiple CLC resonant rectifiers in the receiving side. The CLC resonant rectifiers are connected in parallel to form multiple independent output channels, and each channel is then connected to an LED string. Based on the analysis of the T resonant circuit and the modeling of coupling coils, multiple constant output currents can be derived. As a result, current balance can be achieved, which is very suitable for driving multistring LEDs. The proposed system also offers a modular, scalable, and maintenance-free design, which can significantly reduce the construction cost and the control complexity. In addition, the inverter in the transmitting side can achieve zero phase angle. A laboratory prototype with dual independent output currents is built to verify the proposed method. The experimental results agree well with the theoretical analysis. [ABSTRACT FROM AUTHOR]

Wireless power transfer (WPT) technology has shown its significant role in various applications, such as electric vehicles and consumer electronics. In this paper, an input-parallel output-series circuit topology based on a compact double-sided decoupled coupler is presented to upgrade the power capacity of the WPT system with low-power and low-cost semiconductors. To avoid the potential risk of magnetic saturation, the phase difference between the transmitter currents is controlled to be 90° to achieve a symmetrical magnetic flux distribution for the magnetic coupler. Most importantly, an analytical model, which illustrates the relation between the efficiency and the ratio of the output voltages of the transmitter-side inverters under various misalignments, has been derived. Based on this, a control strategy is developed to maximize the energy efficiency under various misalignment conditions. The experimental results based on a 2.5-kW laboratory prototype show that, in comparison with the traditional method with identical inverters output voltages, the overall efficiency is improved by 2.32% by using the proposed method. [ABSTRACT FROM AUTHOR]

In this letter, a new power and data-parallel transmission method for wireless power transfer (WPT) systems based on a magnetically decoupled coupling structure is proposed. Unipolar coils are used for power transfer, while series-connected perpendicular bipolar coils are used for data transfer. Data transfer coils are placed in overlap with the power transfer coils at both primary side and secondary side, respectively, to form a compact structure. Especially, the side lengths of data transfer coils are intentionally designed to be smaller than the power transfer coils. Thus, in the specific four-quadrant misalignment area, the crosstalk interference between power and data transfer channels can almost be neglected, resulting in a straightforward design of data processing circuit. With the proposed coupling structure, data transfer presents a symmetrical misalignment ability. Moreover, the data transfer channel is utilized to conduct the closed-loop control of output voltage in the WPT system. Thus, in the specific four-quadrant misalignment area, stable power transfer can also be achieved. The feasibility of the proposed power and data-parallel transfer method is verified by a 122-W laboratory prototype. The system efficiency reaches 87% and data transfer rate is 19.2 kb/s. (This letter is accompanied by a video demonstrating the experimental test). [ABSTRACT FROM AUTHOR]

In this letter, a multistring light-emitting diode (LED) driver based on a three-coil wireless power transfer system is proposed. The proposed system can solve the current imbalance problem among multiple LED strings because of its unique merit of multiple load-independent constant current (CC) outputs. Also, zero-phase-angle operation is achieved. Thus, not only the power rating of power switches can be reduced but also the efficiency is improved. For the sake of compactness, the source coil and the transmitter coil on the transmitting side are attached to the same plane. In addition, to further save the install space, magnetically integrated LCL resonators are utilized on the receiving side. The proposed system is cost-effective since only one receiver and passive components are needed to obtain the multiple CC outputs. Furthermore, by employing a master–slave control strategy, the output currents can be changed synchronously, which enables the “plug and play” capability and features a simple control structure. Finally, the feasibility of the proposed method is verified on a laboratory prototype. [ABSTRACT FROM AUTHOR]

In this letter, a compact battery charger based on wireless power transfer (WPT) technology without any communication requirement is proposed. Here, a new intermediate coil is developed to achieve load-independent constant current (CC) and constant voltage (CV) outputs. The intermediate coil is split into two coils and is overlapped with the receiver coil to form a compact structure. Two switches on the receiver side are used to reconfigure the intermediate resonant circuit in order to select different charging modes, i.e., CC mode or CV mode. The communication between the transmitter side and the receiver side as well as complex control strategies is not needed in the proposed structure. Besides, the proposed system can achieve zero phase angle operation, fixed operating frequency, and zero-voltage switching, which not only can lower the power rating of power devices but also improve the efficiency. A laboratory prototype with a 3.6 A charging current and a 48 V charging voltage is built to verify the feasibility of the proposed method. [ABSTRACT FROM AUTHOR]