Method for Adjusting Single Matching Network for High-Power Transfer Efficiency of Wireless Power Transfer System

Abstract

A wireless power transfer (WPT) system is generally designed with the optimum source and load impedance in order to achieve the maximum power transfer efficiency (PTE) at a specific coupling coefficient. Empirically or intuitively, however, it is well known that a high PTE can be attained by adjusting either the source or load impedance. In this paper, we estimate the maximum achievable PTE of WPT systems with the given load impedance, and propose the condition of source impedance for the maximum PTE. This condition can be reciprocally applied to the load impedance of a WPT system with the given source impedance. First, we review the transducer power gain of a two‐port network as the PTE of the WPT system. Next, we derive two candidate conditions, the critical coupling and the optimum conditions, from the transducer power gain. Finally, we compare the two conditions carefully, and the results therefore indicate that the optimum condition is more suitable for a highly efficient WPT system with a given load impedance.

Method for Estimating Optimum Free Resonant Frequencies in Overcoupled WPT System

“…In [7], a switchable capacitor array circuit was proposed, and it was shown that several capacitors were enough to implement a variety of matching cases in an -section matching network. Our group showed that the WPT system can achieve the high PTE by adjusting only the source impedance [8], and we also demonstrated the self-adaptive WPT system achieving the high PTE without the feedback of receiver information [9].…”

“…Figure 2 shows an equivalent circuit model of a twocoil WPT system, where the controllable elements include voltage source V , source impedance R , load impedance R , primary coil 1 , secondary coil 2 , and capacitances of primary and secondary resonators, 1 and 2 . Depending on the circuit elements, various methods have been introduced to improve the PTE and output power of the WPT system [6][7][8][9][10][11][12][13]. These methods are categorized in two types: a method that changes the critical coupling coefficient [6][7][8][9][10] and a method that mitigates the equivalent coupling coefficient in the overcoupled state [11][12][13].…”

Comparative Analysis of Two- and Three-Coil WPT Systems Based on Transmission Efficiency

“…This expression is identical to the PTE of [22], which is derived from the transducer power gain of the two-coil WPT system. Let A = k 2 12 Q 1 Q 2 , then the PTE of the two-coil WPT system can be written as…”

“…Therefore, the transmission efficiency using the transmission coefficient can usually apply to a static WPT system, which has constant system parameters such as constant source and load impedances and constant coupling coefficient. There also have been various attempts to express the transmission efficiency of multi-coil WPT system such as three-and four-coil WPT systems as well as two-coil WPT system in closed form by using the definition of the transducer power gains [4], [22]- [24]. The transmission efficiency of the twocoil WPT system is simply expressed in closed form, but to derive that of WPT system with three or more coils in closed form is very cumbersome.…”

Printed Spiral Resonator for Displacement-Tolerant Near-Field Wireless Energy Transfer

“…Vulnerability of Wireless Energy Transfer (WET) systems in terms of loop orientation should not be overlooked, especially with respect to the effect on its performance metrics specifically coupling coefficient and power transfer efficiency [8]. Attenuation of coupling coefficient is inevitable with the increment of distance due to divergence from critical coupling threshold that does not comply with simultaneous conjugate matching between the source and load impedances resulting in the deterioration of power transfer efficiency [9]. As opposed to ideal situation where receiver loop resonator is positioned at perfect alignment, displacement, be it planar, lateral or angular, often transpires in practical applications [10].…”