Abstract
The performance of a conventional Class-E2-based WPT system is sensitive to system parameters such as the coil coupling coefficient and load variation. System efficiency decreases rapidly when the coil coupling coefficient and load deviate from their optimum values. In this paper, an impedance matching method and a design procedure are proposed to maintain high system efficiency over a wider range of coupling coefficient and load variations. The load-pull technique is adopted to identify the high-efficiency load region of a Class-E power amplifier (PA), and a double-L-type impedance matching network (IMN) is proposed to transform the load impedance of a Class-E PA into a high-efficiency working region. Compared to a single L-type IMN, a double-L-type IMN is more flexible and has better tuning performance. A 6.78 MHz Class-E2-based WPT system was built to validate the proposed design method. The experimental results show that the proposed double-L-type IMN can significantly attenuate the decline in Class-E PA efficiency when system parameters dynamically change. With a double-L-type IMN, the WPT system could maintain high efficiency (over 55%) under a wider range of coil coupling coefficient and load variations. The peak system efficiency reached 83.2% with 13.7 W output power. The impedance matching method and design procedure in this paper could provide a practical solution for building a high-efficiency WPT system with strong robustness.
Highlights
In recent years, inductive wireless power transfer systems have been widely used in mobile devices, such as cell-phones, smart watches, and earphones
In terms of output power, the maximum output power double-L-type impedance matching network (IMN), the Class-E2-based wireless power transfer (WPT) system has strong robustness and can of the WPT system is improved with an IMN
A double-L-type IMN is added between the Class-E power amplifier (PA) and transmitting coil, which is employed to maintain the high efficiency of the Class-E PA under a wider range of coupling coefficients and load variations
Summary
Inductive wireless power transfer systems have been widely used in mobile devices, such as cell-phones, smart watches, and earphones. To improve the user experience, medium-range wireless power transfer (WPT) and multiple device charging technologies have attracted considerable attention from both academia and industry It will be promising for consumer electronics to achieve longer transmission distances in WPT systems by increasing the system frequency to megahertz. The parameters of a Class-E rectifier need to be carefully designed with DC load variation [15] Various adaptive methods, such as adaptive frequency regulation, adaptive load regulation, and adaptive impedance matching, have been developed to improve the performance of a WPT system with dynamically changing coil distances and loads. A fixed double-L-type IMN is proposed in this paper to transform load impedance into a high-efficiency working region. A novel double-L-type IMN is proposed in the design of a Class-E2-based WPT system. The simulation results of Class-E2-based WPT systems with/without double-L-type IMN are are compared.
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