In this paper we describe a geometry design solution to minimize performance variations of a wireless power transfer system "on the move" (WPT-Mob). A sequence of switchable couples of coils, connected in series or in parallel, is adopted at the fixed transmitting link side; the geometry of the moving receiver is optimized to keep the coupling factor, and thus the power transfer, constant during the movement. First the analytical formulation of the link coupling factor is derived as a function of its circuit-equivalent parameters computed by fullwave simulation. Then selected geometry parameters of the receiver side are optimized to keep the coupling factor constant while the link is moving. A set of TX-RX arrangements are simultaneously analysed to emulate the sliding movement of the WPT-Mob. The final optimized geometry demonstrates that a constant power transfer on-the-move is enabled, even for variable TX-to-RX link distances. Design and experimental verification are carried out for a geometry suitable for medium power transfer (tens of Watts) at 6.78 MHz, but the method is formulated in such a way that the system can be scaled up and down to accomplish different application needs.
This paper describes the modeling, analysis, and design of a complete (dc-to-dc) inductive wireless power transfer (WPT) system for industrial moving applications. The system operates at 6.78 MHz and delivers up to 150 W to a load moving along a linear path, providing a quasi-constant dc output voltage and maintaining a zero voltage switching operation, regardless of position and load, without any retuning or feedback. The inductive link consists of an array of stationary transmitting coils and a moving receiving coil whose length is optimized to achieve a constant coupling coefficient along the path. Each Tx coil is individually driven by a constant amplitude and phase sinusoidal current that is generated from a GaN-based coupled load-independent Class EF inverter. Two adjacent transmitters are activated at a given time depending on the receiver’s position; this effectively creates a virtual series connection between the two transmitting coils. The Rx coil is connected to a passive Class E rectifier that is designed to maintain a constant dc output voltage independent of its load and position. Extensive experimental results are presented to show the performance over different loading conditions and positions. A peak dc-to-dc efficiency of 80% is achieved at 100 W of dc output power and a dc output voltage variation of less than 5% is measured over a load range from 30 to 500 Ω . The work in this paper is foreseen as a design solution for a high-efficient, maintenance-free, and reliable WPT system for powering sliders and mass movers in industrial automation plants
This paper will present the design of a positionindependent inductive wireless power transfer (WPT) system for dynamic applications, where power is required to be delivered to a moving object on a path, such as industrial sliders and mass movers. A key feature of the designed inductive WPT system is to inherently maintain a constant dc output voltage, dc output power and dc-to-dc efficiency of the overall system, regardless of the vehicle's position. The system consists of an array of transmitting coils, where each coil is driven by a 6.78 MHz constant amplitude current generated from a load-independent Class EF inverter. The receiving coil is series tuned and is connected to a Class EF2 rectifier, which is numerically optimised to maintain a constant dc output, independently of the dc load. The system is powered from a 70V dc voltage source. GaN FET and SiC diodes are used to implement the Class EF inverter and rectifier. Results show a peak dc-dc efficiency of 83% at 150W with a 4% variation of the output voltage. The prototype of the complete link is under way.
The idea of this paper is to develop a moving resonant wireless power transfer (WPT) system capable of keeping the coupling factor, and thus the power transfer, invariable with respect to the reciprocal system sides positions. A typical scenario is the WPT to moving objects on a platform equipped with a sequence of coils underneath. If a single TX coil is active at a time, the receiver movement would cause the coupling coefficient, and consequently the transmitted power, to oscillate. To cope with this problem, in this work we propose to make use of two active Tx coils. Different coil geometries and coil connections have been investigated, trying to get an insight into the coupling mechanism. This have been done by full-wave simulations and measurements of the selected structures and by varying some key parameters of the geometry itself. The connections between coils have been done in post-processing and the results have been plotted for comparison. Future work has been proposed.
An increasing interest is arising in developing miniaturized antennas in the microwave range. However, even when the adopted antennas dimensions are small compared with the wavelength, radiation performances have to be preserved to keep the system-operating conditions. For this purpose, magneto-dielectric materials are currently exploited as promising substrates, which allows us to reduce antenna dimensions by exploiting both relative permittivity and permeability. In this paper, we address generic antennas in resonant conditions and we develop a general theoretical approach, not based on simplified equivalent models, to establish topologies most suitable for exploiting high permeability and/or high-permittivity substrates, for miniaturization purposes. A novel definition of the region pertaining to the antenna near-field and of the associated field strength is proposed. It is then showed that radiation efficiency and bandwidth can be preserved only by a selected combinations of antenna topologies and substrate characteristics. Indeed, by the proposed independent approach, we confirm that non-dispersive magneto-dielectric materials with relative permeability greater than unit, can be efficiently adopted only by antennas that are mainly represented by equivalent magnetic sources. Conversely, if equivalent electric sources are involved, the antenna performances are significantly degraded. The theoretical results are validated by full-wave numerical simulations of reference topologies.
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