Abstract
Radio Frequency Wireless Power Transfer (RFWPT) systems operating at higher frequencies such as 6.78 MHz are drawing a lot of attention due to their advantages such as the improved user convenience, the compact size and the light weight. In a WPT charging system the DC/DC converter, which provides an accurate voltage and current to the battery is essential for its safety and lifespan. This paper presents the design and implementation of a high efficiency, light weight-Megahertz WPT system that makes it possible to charge Lithium Batteries by Constant Current (CC) and Constant Voltage (CV) charging with a pair of coils. The proposed WPT charger is simple in structure since it does not require a feedback circuit to implement CC/CV charging. Hence, no communication between the primary side and secondary side is needed. Since the charger can provide automatic mode transfer from CC to CV charging, the battery can be fully charged without the help of an additional DC/DC converter. Simulation and experimental results obtained with a 50W WPT charger operating at 6.78-MHz are presented to verify the feasibility and the validity of the proposed method.
Highlights
The Wireless Power Transfer (WPT) technology has become more and more popular for electronic devices since it can eliminate the inconvenience of traditional plug-in chargers by removing the connection wire between the charger and the devices to be charged [1]
OPERATION PRINCIPLE OF THE PROPOSED WPT CHARGER In the proposed WPT topology an S-LCC resonant network is utilized for implementing Constant Voltage (CV) charging and an S-LCC + LCL resonant network is used for implementing Constant Current (CC) charging
In this paper a compact hybrid topology for the CC/CV charge of a WPT charger system operating at 6.78 MHz has been proposed
Summary
The Wireless Power Transfer (WPT) technology has become more and more popular for electronic devices since it can eliminate the inconvenience of traditional plug-in chargers by removing the connection wire between the charger and the devices to be charged [1]. To realize CC/CV in a high frequency WPT charger, closed-loop control can be implemented with frequency modulation with a single stage converter or an additional back-end DC-DC converter in the receiver side Those methods increase the cost, complexity and power loss of the system [8]–[10]. There are four basic compensation topologies, series-series (SS), series-parallel (SP), parallel-series (PS) and parallel-parallel (PP), which can be introduced for the CC/CV charge of a WPT system With these resonant compensation circuits, the instinctive Zero Phase Angle (ZPA) condition can be achieved with load independent constant voltage and constant current output characteristics [12]. High efficiency can be achieved thanks to its soft switching characteristics over a wide range of loads and the absence of a back-end DC-DC converter It is flexible in implementing CC/CV charging with different design specifications due to its high order resonant compensator.
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