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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]

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]

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]