Extended-Distance Wireless Power Transfer System with Constant Output Power and Transfer Efficiency based on Parity-Time-Symmetric Principle
Abstract : Maintaining constant power transfer while keeping near-unity transfer efficiency at varying transfer distances is a major challenge for existing wireless power transfer (WPT) system with multiple repeaters. In order to overcome the problem, this article proposes a novel WPT mechanism with multiple repeaters based on the concept of parity-time symmetry. First, the coupled-mode model of this WPT relay system is established. Then, the steady-state transfer characteristics of the proposed WPT system with an odd and even number of repeaters are analyzed. The theoretical analysis shows that whether an odd or even number of repeaters are inserted between the transmitting and receiving coils, the proposed system automatically achieves constant output power and transfer efficiency against the variation of the transfer distance without any tuning or feedback within a certain distance. The prototype with one repeater and two repeaters is implemented to verify the validity of the theoretical analysis. Experimental results show that the prototype with one repeater can transfer power with an invariant transfer efficiency of 91% and a constant output power of 15 W within a transfer distance of 420 mm. Similarly, the prototype with two repeaters transfers constant power of 15 W over a transfer distance ranging from 420 to 500 mm, and the transfer efficiency is constant near 89%.
? According to the relative magnitude of the operating frequency, these branches are called the high-frequency branch, the mid-frequency branch and the low-frequency branch.
? Moreover, although the mid-frequency branch of the system theoretically exists when ? < 0, it cannot be observed in the experiment due to its instability.
? Wireless power transfer (WPT) is a technique that transmits power without contact and is the main method for making electrical devices wireless.
? WPT systems are widely favored by the public due to their high portability and flexibility.
? The electrochemical fatigue or the heat damage of battery could change the load resistance or capacitance. In this case, the two bifurcating eigenfrequencies in the TO-PT circuit can be exploited for monitoring the receiver’s status (i.e., by measuring the resonance shift and the battery lifetime.
? While the WPT technology has motivated considerable research and development in the past two decades, there are still several fundamental issues which need further investigation to maximize the potential of this technology.
? Traditional WPT systems are not robust against alteration of distance and misalignment between coils [5,16], and variations in the terminating impedance of an electric power grid or battery over time
• A new type of current mode NPTS-WPT was proposed in , focusing on the factors affecting the critical coupling coefficient.
• The results show that the current mode NPTS-WPT has similar transfer characteristics to the system proposed in , and is more suitable for the case of smaller load resistance and higher current requirements. References innovate and explore the topology of NPTS circuit.
• The reactance mismatch caused by detuning can have great influence on the system output power and efficiency so that the performance of the overall system will degrade accordingly .
? In this system, high-efficiency power transfer always takes place at ?0, and the performance is rather insensitive to the offset between the receiver and the transmitting module (i.e., ? variations) and to changes in the receiver’s load impedance (which causes ? variations).
? Besides, the range of inductive power transfer remains a principal challenge. In spite of advances in various coil designs and the capability to create spatial Bessel beams, it remains difficult to overcome the performance deterioration due to the poor tolerance in coil misalignment, especially in the weak-coupling regime .
? A fundamental challenge for the nonradiative wireless power transfer (WPT) resides in maintaining the stable power transmission with a consistently high efficiency under dynamic conditions.
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