See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/312087881 Sensing Movable Receiving Coils by Detection of AC Current Changes on the Primary Side of a Multi-Coil System Article in Procedia Engineering · January 2017 DOI: 10.1016/j.proeng.2016.11.323 CITATIONS READS 0 54 4 authors, including: Bilel Kallel Olfa Kanoun Technische Universität Chemnitz Technische Universität Chemnitz 9 PUBLICATIONS 15 CITATIONS 353 PUBLICATIONS 832 CITATIONS SEE PROFILE SEE PROFILE Hafedh Trabelsi Ecole Nationale d'Ingénieurs de Sfax 46 PUBLICATIONS 81 CITATIONS SEE PROFILE Some of the authors of this publication are also working on these related projects: Electrode design optimisation for enhanced pressure sensitivity View project Image postprocessing with decision trees of reconstructed Images of electrical impedance tomography reconstructed with EIDORS View project All content following this page was uploaded by Bilel Kallel on 05 January 2017. The user has requested enhancement of the downloaded file. All in-text references underlined in blue are added to the original document and are linked to publications on ResearchGate, letting you access and read them immediately. Available online at www.sciencedirect.com ScienceDirect Procedia Engineering 168 (2016) 991 – 994 30th Eurosensors Conference, EUROSENSORS 2016 Sensing Movable Receiving Coils by Detection of AC Current Changes on the Primary Side of a Multi-Coil System B. Kallela,b*, O. Kanouna, H. Trabelsib, M. Roesc a Chair for Measurement and Sensor Technology, Technische Universität Chemnitz, Reichenhainer Straße 70, 09126 Chemnitz, Germany Computer, Electronic & Smart Engineering systems design, National Engineering School of Sfax, Road of Soukra km 3, 3038 Sfax, Tunisia c Electromechanics and Power Electronics, Eindhoven University of Technology, Postbus 513, 5600 MB Eindhoven, The Netherlands b Abstract Position detection is very important for inductive power transfer systems with movable receivers, in order to switch off inactive coils and to reach a high efficiency. The solution presented in this paper is based on the measurement of the current amplitudes in sending coils, which show a significant difference between no targets, metallic targets and receiving coils. A galvanically separated circuit is designed to implement the new method by transforming the current of the sending coils to a DC voltage and then comparing it to the detection threshold. Finite element simulations were carried out to predict the value of the detection threshold. Both simulation and experimental results show that the circuit fulfils the detection requirements with high precision and high detection height. The proposed method represents a smart, efficient and low cost detection technique for inductive systems with a movable receiver, independently on position and speed. © Published by Elsevier Ltd. This © 2016 2016The TheAuthors. Authors. Published by Elsevier Ltd.is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of the 30th Eurosensors Conference. Peer-review under responsibility of the organizing committee of the 30th Eurosensors Conference Keywords: Inductive power transmission; Multi-coil system; Movable receiver; Position detection 1. Introduction Inductive power transmission IPT is used for different power range applications including biomedical implants [1], battery recharging of electrical vehicles [2] as well as powering autonomous sensors [3] and portable electronic * Corresponding author. Tel.: +49-371-531-34857; fax: +49-371-531-834857. E-mail address: [email protected] 1877-7058 © 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of the 30th Eurosensors Conference doi:10.1016/j.proeng.2016.11.323 992 B. Kallel et al. / Procedia Engineering 168 (2016) 991 – 994 devices [4]. In case of movable receiver, the two-coil inductive system is no more suitable for power transmission and it is proposed to use multi-coil inductive system. Multi-coil inductive link is one of the most promising methods of energy transfer because it provides a safe, convenient and flexible power transfer technology [5 - 7]. However, powering all sending coils simultaneously decreases system efficiency due to the high loss of magnetic field. To overcome this problem a receiver detection system is required and only the coils that are underneath the receiver should be powered. The design of such a system presents a very challenging task for which only few methods were proposed in literature. In [8], authors have proposed a load-detection method to reduce the power consumption of an inductive system by analyzing the transmitting coil voltage and supply current space using a microcontroller with a built-in ADC. Their aim is to turn off the sending coils when no valid receiving devices is placed on the transmitting platform. The low detection height of this method presents its major limitation. In [9] a detection method was proposed using additional coils located in every transmitter coil. Sensing principle is based on the detection of ferrite material in the receiver that increases the inductivity of the additional coils and thus reduces the resonance frequency. However, this method shows some drawbacks due to the necessity to use of receivers covered by ferrite material and the low detection height. In [10], a detection method was proposed, which is based on the measurement of the impedance change of sending coils. Changes of impedance amplitudes and phases can be detected by measuring the voltage and the current of every sending coils. For that, the AC voltages are measured and at the same time, the load type can be estimated. However, this solution requires four extra estimation circuits attached to each sending coil and other electronic components that increase the system complexity and cost. In this paper, we present an effective solution to reduce the power consumption of a multi-coil inductive system in case of no load and metallic targets present on the transmitter platform. This is by powering only the coils underneath the valid receiver which is the receiving coil. The proposed solution overcomes the use of any additional sensors or coils. It is realized by introducing only simple circuits and uses the sending coils themselves as detectors. Fig. 1 (a) depicts the studied multi-coil systems. Sending coils are similar. Every coil has a diameter of 3 cm and 4 turns. The receiving coil has a dimeter of 6 cm and 8 turns. The vertical distance separating the two sides equals to 5 cm. This is to perform a high detection height. b a Fig. 1. (a) Studied multi-coil inductive system (b) sending coil S1 current for different load types 2. Implemented detection method The proposed solution consists of the measurement of the peak of the AC current of every sending coils, converts it into DC voltage value and then compare it to a threshold limit which is dependent, in general, on the supply voltage, the sending coil parameters as well as on the receivers. In order to predict the current value of the sending coil, finite element simulations were carried out. Results presented in Fig. 1 (b) demonstrate a significant difference between no loads (without receiver), metallic targets (conductive material) and receiving coils (valid receiver). They show that the current amplitude decreases only in the case of the presence of a receiving coil in the proximity. Based on the aforementioned results, a detection threshold can be chosen between 0.61A and 0.73A. B. Kallel et al. / Procedia Engineering 168 (2016) 991 – 994 The system converts, first, the AC current circulating in the sending coil to a DC voltage and then compares it to a reference voltage. The reference voltage is chosen within the gap between the voltage thresholds corresponding to the case of a valid and invalid load. For a threshold current of 0.66 A (see Fig. 1 (b)), a detection voltage threshold “Vref” of 2.4 V was chosen. Fig. 2. Detection circuit Fig. 2 depicts the designed detection circuit. Via a toroidal transformer, the current in the sending coil is transferred to a galvanically separated circuit. The measured current in the secondary side after the transformer is converted to a voltage “Vcoil” by a simple peak detector circuit and then compared to the detection voltage threshold “Vref”. A timer and flip-flop circuits were added to periodically test for valid loading conditions when the transmitting coil is switched off. The time interval for detection can be adjusted by the user by modifying the value of resistances R3 and R4 and the capacitor C2. Fig. 3. Laboratory set-up for the sensing circuit Fig. 3 shows the laboratory set-up for the sensing circuit. A ferrite ring was used for the toroidal transformer, two integrated circuits NE555 and one LM311P are used for the timer, flip-flop and comparator respectively. In order to test the circuit experimentally, an AC voltage generator was used. 3. Results and discussions Two current values corresponding to the sending coil current are programmed as an input to the designed detection circuit. After transformer and AC/DC conversion, two voltage values are obtained: 1.5 V which indicates the presence 993 994 B. Kallel et al. / Procedia Engineering 168 (2016) 991 – 994 of valid load and 3.4 V which indicates either no load or invalid load (see Fig. 4, black signal). A short time interval was chosen for the evaluation of the circuit to clearly identify its two operation modes. The timer and flip-flop are also programmed to test every 1.8 ms for valid loading conditions when the transmitting coil is switched off. This value could be changed by the user and depending on the velocity of the receiver. The green lines of fig. 4 represent the output voltage for the inverter’s driver. It is clear that if Vcoil > Vref so the output voltage Vout = 0 V and if Vcoil < Vref so the output voltage Vout = 1 V. The choice of the value of Vout is only to check the good operation of the circuit. It could be changed to another value chosen by the user. The main advantages of the designed circuit that it requires no communication link between the sending and receiving sides and its high detection height which equals to 5 cm. Fig. 4. Simulation results of the implemented detection circuit 4. Conclusion In this paper, a detection circuit for movable receiver of a multi-coil inductive system is designed. It consists of the measurement of AC current peak of every sending coils, converts it into DC voltage value and then compare it to a threshold limit. The coil current threshold is predicted by finite element simulation. Both simulation and experimental results show that the designed circuit fulfils the detection requirements. It presents an efficient, low cost detection technique which is also suitable for high distances. Additionally, it doesn’t require any communication link between the sending and receiving sides. References [1] E. K. F. Lee, A discrete controlled fully integrated class E coil driver with power efficient ASK modulation for powering biomedical implants, IEEE Trans.Circuits Syst. I: Reg. Papers 62 (2015) 1678–1687. [2] X.T. García, J. Vázquez, P.R Sánchez, Design, implementation issues and performance of an inductive power transfer system for electric vehicle chargers with series–series compensation, IET Power Electron. 8 (2015) 1920–1930. [3] B. Kallel, T. Keutel, O. Kanoun, MISO configuration efficiency in inductive power transmission for supplying wireless sensors, IEEE 11th Int. Multi-Conf. on Systems, Signals & Devices (2014) 1–5. [4] H.H. Wu, G.A. Covic, J.T. Boys, D.J. Robertson, A Series-tuned inductive-power-transfer pickup with a controllable AC-voltage output, IEEE Trans. Power Electron. 26 (2011) 98–109. [5] B. Kallel, O. Kanoun, H. Trabelsi, Large air gap misalignment tolerable multi-coil inductive power transfer for wireless sensors, IET Power Electron. (2016) DOI: 10.1049/iet-pel.2015.0800. [6] D. Ahn, S. Hong, Effect of coupling between multiple transmitters or multiple receivers on wireless power transfer, IEEE Trans. Ind. Electron. 60 (2013) 2602–2613. [7] W.X. Zhong, X. Liu, S.Y.R. Hui, A novel single-layer winding array and receiver coil structure for contactless battery charging systems with free-positioning and localized charging features, IEEE Trans. Ind. Electron. 58 (2011) 4136–4144. [8] Z. N. Low, J. J. Casanova, P. H. Maier, J. A. Taylor, R. A. Chinga et al., Method of load/fault detection for loosely coupled planar wireless power transfer system with power delivery tracking, IEEE Trans. Ind. Electron. 57 (2010) 1478-1486. [9] E. Waffenschmidt, T. Staring, Limitation of inductive power transfer for consumer applications, in Proc. 13th Eur. Conf. Power Electron. Appl. (2010) 1-10. [10] C. L. W. Sonntag, J. L. Duarte, A. J. M. Pemen, Load position detection and validation on variable-phase contactless energy transfer desktops, IEEE Energy Conversion Congress and Exposition (2009) 15-27. View publication stats
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