International Journal of Electrical and Computer Engineering (IJECE) Vol. 8, No. 3, June 2018, pp. 1331 – 1335 ISSN: 2088-8708 1331 Institute of Advanced Engineering and Science The Interaction between Load Circuits and Decision of Frequency for Efﬁcient Wireless Power Transfer Kazuya Yamaguchi Department of Control Engineering, National Institute of Technology, Nara College, Japan Article Info Article history: Received: Dec 14, 2017 Revised: Feb 6, 2018 Accepted: Feb 22, 2018 Keyword: wireless power transfer coupling coefﬁcient state space representation ABSTRACT This paper derives an expression of efﬁciency of wireless power transfer on a situa- tion that there are two devices towards one AC power supply. The interaction between a power supply and load is paid attention on a conventional wireless power transfer system, in contrast, the interaction between loads must be taken account of on the sit- uation too. This is attributed to a possibility that a load disturbs the energy transmitted from a power supply to another load. Moreover each load needs different frequency of power supply for the ideal transfer since they have different natural frequencies on many situations. This paper models a circumstance that there are a power supply and two loads with a state space equation, and proposes how to decide a frequency of power supply to realize efﬁcient transfer for each load. Copyright c  2018 Institute of Advanced Engineering and Science. All rights reserved. Corresponding Author: Kazuya Yamaguchi Department of Control Engineering, National Institute of Technology, Nara College 22 Yata-cho, Yamatokoriyama, Nara, JAPAN Email: k-yamaguchi@ctrl.nara-k.ac.jp 1. INTRODUCTION Wireless Power Transfer (WPT) system is focused on the areas of energy, information, communica- tion, and control, etc. In WPT, electric power is transferred on electromagnetic ﬁeld by coils based on some electromagnetic theory. The basic theory of transfer electromagnetically was established by Nikola Tesla[1], and WPT is researched actively from the study of WPT on strongly coupled magnetic resonance[2]. The various methods are attempted according to some papers to improve efﬁciency and power, and to reduce energy loss of WPT. [3] focuses on circuit topology, and it mentions that the combination of series or parallel of circuit affects the intensity of power. A phase difference between the two transmission coils is controlled to increase efﬁciency[4]. The several coils are utilized for transmission of power to enlarge power, efﬁciency, and the distance between a power supply and loads[5][6]. Moreover WPT is applied for the various devices, places, and situations. In the medical area, a capsule endoscopy is charged from the outside of human body[7], and an effect to human body is investigated because the electromagnetic wave is generated on transmission wirelessly[8]. In the area of semiconductor, an application of WPT for the semiconductors is examined on low power and high frequency[9]. In terms of the long distance transmission, charge from a power supply on the ground to a balloon at high altitude is reviewed with electric propulsion[10]. As a merit of WPT, charging several devices simultaneously by closing them near a power supply is listed since WPT system does not need any connection of wire. However, when the device A is charged by a power supply, the other device B which is put near A may disturb exchanging energy between the power supply and A. Therefore the interaction between devices must be investigated in addition to the transmission of energy from power supply to loads[11]. In this paper, the exchange of energy between a power supply and two loads is analyzed with a mathe- matical model based on modern control theory. Especially the coupling coefﬁcients between a transmitting coil and device coil, and between device coils are focused for ﬁnding transportation efﬁciency. Finally, the effect of Journal Homepage: http://iaescore.com/journals/index.php/IJECE w w w . i a e s j o u r n a l . c o m