Network Methods for Analysis and Design of Resonant Wireless Power Transfer Systems

In this chapter we illustrate networks methods for the analysis an design of Wireless Power Transfer (WPT) systems. We begin with an introduction which compares the alternatives available for transfering electromagnetic power. In particular, we illustrate the advantages and disadvantages of the various possibilities: transmission lines, antennas, and mid-range reactive field couplings. Then, in the introduction, we also illustrate practical applications for WPT and discuss relevant papers published so far. In the second section, after introducing a basic structure for realizing WPT (see Fig.1), we discuss the relevant theory for WPT by considering a very simple network which, nevertheless, contains all the relevant phenomenology. We derive formulas for maximizing the efficiency of power transfer and we show the necessity of introducing matching networks. Several possible realizations of matching networks are then illustrated. In the next section we introduce appropriate methods, based on the ABCD matrix, for the narrow-band analysis of WPT systems including matching networks. An example of such a network is reported in Fig. 2. A section will be devoted to the input and output coupling design where we will provide new formulas for the design of the matching networks. In particular we show that, for a given type of resonators with a given quality factor Q and a given value of the coupling between the two resonators, we can find the optimal coupling coefficients which maximize the efficiency. An example of the results achievable when optimizing the input/output coupling is reported in Fig. 3. Having derived a procedure for attaining maximum efficiency, it is also possible to establish the theoretical limits that can be achieved for a given value of coupling and for specified values of the resonators Q. A section will be also devoted to the case of multiple transmitting and multiple receiving resonators. For this arrangement, which has practical relevance and is illustrated in Fig 5, we also introduce a rigorous general network model for its analysis. Several different types of resonators will be investigated and compared. Closed form formulas relevant to the resonators' design will be introduced and also fullwave analysis of resonators well be exploited. Theoretical results will be compared with measured ones and measurement methods will be discussed. One of the problems of WPT, i.e. the frequency shift occurring when resonators are placed at different distances, will be discussed and the solution will be outlined. This is very important in practice because allows to realize systems without the need of complex sources or difficult tracking mechanisms. Finally, we will also illustrate how to analyze, both in frequency and time domain, the network representations used for WPT

A Network Approach for Wireless Resonant Energy Links Using Relay Resonators

In this paper, a network approach for the analysis of a wireless resonant energy link consisting of N inductively coupled LC resonators is proposed. By using an artificial transmission line approach, the wireless link is modeled as a transmission line described by effective parameters. It is shown that the analyzed system exhibits a passband filter behavior. More specifically, the reported results demonstrate that in the wireless link passband the effective parameters assume negative values resulting in a negative phase delay. Useful design formulas are derived and validated by comparisons with the experimental data

Coupling-Independent Wireless Power Transfer

It is well known that mid-range wireless power transfer can be realized by a link consisting of mutually coupled series resonant circuits operating at the common resonant frequency. However, in such conditions, the link load which maximizes the output power or the transfer efficiency is coupling dependent. This letter provides an analytical solution to this problem by exploiting the frequency bifurcation phenomenon, which occurs after a certain threshold value of the coupling. When the system is operated at one of the secondary resonances, it behaves as an ideal transformer; thus, it is able to deliver to a prescribed load constant output power with constant efficiency. This is true for variable coil distances or coil misalignment, that is, for variable coupling coefficient

Electromagnetic field computation by network methods

This monograph proposes a systematic and rigorous treatment of electromagnetic field representations in complex structures. The book presents new strong models by combining important computational methods. This is the last book of the late Leopold Felsen

Harmonic balance design of wireless resonant-type power transfer links

none4noHarmonic-balance (HB) based nonlinear techniques are exploited for the design of a high-efficiency and medium-power switching mode oscillator, used as continuous power source in a wireless power transmission system. The oscillator power is transmitted through resonant coils over variable distances. To account for the resonant frequency variations, which also tune oscillation frequency, a broadband design of the system is carried out with the oscillator load including the resonant coupling and the rectifier. The oscillator efficiency, the RF-to-DC system efficiency and the DC power are then directly optimized for any coupling distance of interest. A Royer-type oscillator is designed and prototyped using the proposed technique. The oscillator exhibits 40 W at 223 kHz with 75% conversion efficiency while the WPT system efficiency, DC-to-DC, is better than 60% for coupling distances of the order of 10 cmmixedF. Mastri; A. Costanzo; M. Dionigi; M. MongiardoF. Mastri; A. Costanzo; M. Dionigi; M. Mongiard