A simple method to determine the performance of two-coil wireless power transfer systems without direct output measurement

Abstract

Two-coil wireless power transfer (WPT) systems are composed of two circuits tuned at the same resonance frequency, one containing the source, and other containing the load, both connected to each other by the mutual inductance. The power delivered to the load circuit (𝑷 𝑶 ) divided by the total power supplied by the source (𝑷 𝑻 ) and by the maximum ideal amount of power which can be delivered to the load circuit are usual figures of merit known as efficiency (𝜼) and power transfer capability (𝑷 * ), respectively. Additionally, it can be defined a third figure of merit (𝑰 * ) as the power dissipated at the source circuit divided by 𝑷 𝑻 .It has been recently demonstrated that 𝜼 and 𝑷 * are related to 𝑰 * . In this paper, it is presented a simple method to monitor 𝑰 * , allowing consequently the determination of 𝜼 and/or 𝑷 * without any direct measurement at the load circuit. The qualities and limitations of the proposed method are discussed in details. Practical results are included to verify the proposal.Index Terms-Wireless power transfer, inductive power transfer, figures of merit, efficiency, power transfer capability. I. INTRODUCTIONIRELESS power transfer (WPT) systems via inductive coupling was first reported by Tesla more than a century ago [1]. The simplest WPT systems are composed of only two resonant circuits tuned at the same resonance frequency, one containing the source, and other containing the load, which are magnetically connected by the mutual inductance. Due to its safety, flexibility, and reliability, WPT systems have become a key technology in several fields, such as, for instance, power charging electric vehicles and implantable medical devices [2]-[7].