Conjugate Image Theory Applied on Capacitive Wireless Power Transfer

Abstract

Wireless power transfer using a magnetic field through inductive coupling is steadily entering the market in a broad range of applications. However, for certain applications, capacitive wireless power transfer using electric coupling might be preferable. In order to obtain a maximum power transfer efficiency, an optimal compensation network must be designed at the input and output ports of the capacitive wireless link. In this work, the conjugate image theory is applied to determine this optimal network as a function of the characteristics of the capacitive wireless link, as well for the series as for the parallel topology. The results are compared with the inductive power transfer system. Introduction of a new concept, the coupling function, enables the description of the compensation network of both an inductive and a capacitive system in two elegant equations, valid for the series and the parallel topology. This approach allows better understanding of the fundamentals of the wireless power transfer link, necessary for the design of an efficient system.

Optimal Analytical Solution for a Capacitive Wireless Power Transfer System with One Transmitter and Two Receivers

“…Wireless power transfer for two receivers may be realized by modeling the load as admittances Y 2 and Y 3 . The CWPT link can be described by the coupled capacitances C 1 , C 2 and C 3 [14,23,24].…”

“…We consider the system of Figure 2 with one transmitter and two capacitive coupled receivers. If we assume a system composed of a large aluminum transmitter with aluminum receiver plates of 10 cm × 10 cm, coated with polyethylene as a dielectric material, at a distance of 2.5 mm between transmitter and receiver, we can assume the representative values of Table 2 [14,24]. Using Equations (1), (2), and (10)- (12), the values of the coupling factors, resonance inductances, and auxiliary variables are calculated (Table 3).…”

“…Applications are the charging of, for example, electric vehicles [8], automatic guided vehicles [9], biomedical implants [10], integrated circuits [11] and low-power consumer applications [12]. Compared to IWPT, it has several advantages, such as a reduced cost and weight and the ability to transfer energy through metal [13,14]. Just as for IWPT, CWPT allows for the charging of multiple receivers at once with one transmitter.…”

A High-Efficient Low-Cost Converter for Capacitive Wireless Power Transfer Systems

“…However, the CPT systems have many important benefits that they are cheaper to implement, less vulnerable to metal barriers and electromagnetic interference (EMI), and more flexible with alignment than IPT systems [12]. Thanks to these advantages, the CPT systems have been adopted to various applications, such as biomedical microsystem [5], robot [13], and portable respiratory devices [14], rotating device [15,16] and so forth.…”

“…The IPT is based on magnetic coupling between the winding coils, namely this technique uses the magnetic field to transfer power via air between resonators composed of the isolated windings [1,3,4]. On the other hand, the CPT is based on electric coupling between two metal plates, so that it uses electric field to transfer power through physical isolation barrier that utilizes the capacitance of capacitive interface [5][6][7][8][9][10][11][12].…”