Smith chart impedance matching2/28/2023 ![]() ![]() ![]() ![]() When operated in a megahertz system, a soft-switching Class-E rectifier has smaller switching losses and harmonics content than hard-switching rectifiers. In terms of rectifiers, a soft-switching Class-E rectifier is employed in the Class-E2-based WPT system. In practice, the problem is that the load impedance of a Class-E PA is dynamically changed with uncertainties such as coil misalignment and load variation in multiple device charging, which lead to a decline of efficiency. The performance of a Class-E PA deteriorates rapidly when its load impedance deviates from the optimum value. However, the design method for a Class-E PA is only valid under a fixed load. The well-designed Class-E PA and rectifier are operated in zero-voltage-switching (ZVS) and zero-voltage-derivative-switching (ZDS) modes, achieving higher efficiency than hard-switching topologies. ![]() For a megahertz WPT system, a soft-switching-based Class-E2 DC-DC converter composed of a Class-E power amplifier (PA) and a Class-E rectifier is appropriate. However, conventional hard-switching inverters and rectifiers, such as full-bridge inverters and rectifiers, suffer from large switching losses and harmonics when applied in megahertz WPT system. Therefore, megahertz WPT systems are discussed in this paper. Higher-frequency WPT technologies, i.e., gigahertz WPT technologies, are being developed for use in nanoscale and ultra-low-power systems for biomedical applications, wireless sensors, and microwave detection, which require far less power than the mobile devices mentioned above. Furthermore, compared to kilohertz WPT systems, megahertz WPT systems will be more compact, which is advantageous when charging multiple devices simultaneously. It will be promising for consumer electronics to achieve longer transmission distances in WPT systems by increasing the system frequency to megahertz. 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. In recent years, inductive wireless power transfer systems have been widely used in mobile devices, such as cell-phones, smart watches, and earphones. 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. The peak system efficiency reached 83.2% with 13.7 W output power. 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 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. A 6.78 MHz Class-E2-based WPT system was built to validate the proposed design method. Compared to a single L-type IMN, a double-L-type IMN is more flexible and has better tuning performance. 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. 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. System efficiency decreases rapidly when the coil coupling coefficient and load deviate from their optimum values. The performance of a conventional Class-E2-based WPT system is sensitive to system parameters such as the coil coupling coefficient and load variation. ![]()
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