无线充电技术要点 WPT

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Fig. 1. Proposed transmitting side (DC bus system).
I. I NTRODUCTION Wireless power transfer (WPT) via magnetic resonant coupling was invented in 2007 by MIT [1]. That gave an enormous impact to the world and the technology is being researched all over the world nowadays. WPT technology has huge potential to be applied to many kinds of fields such as transportation, home appliances [2], medical appliances [3] and so on. Especially among them, the application to electric vehicles (EVs) is one of the hottest topics in WPT society [4], [5]. That is because WPT is able to solve the problems that EVs potentially has such as its short cruising range, long charging process. Therefore, static wireless power transfer for EVs (wireless charging when EVs are not in motion) has been researched from many kinds of point of view: coil structure [6], circuit configuration [7], the control method of power converter [8]. Furthermore, dynamic wireless power transfer (DWPT) (wireless charging while EVs are in motion) has been attracting more attention in recent years. With DWPT, EVs would be able to obtain longer cruising distance because they can travel while receiving power from infrastructure. Moreover, they do not need to carry a large amount of heavy and bulky batteries, which leads to the reduction of the EVs’ cost. In order to propagate DWPT as a substitute for normal charging, it has to be simple and easy to install. On the other hand, the secondary side can be complex and should optimize power transmitting characteristic. For instance, transmitting efficiency can be optimized by adjusting the secondary voltage to optimal voltage with power converters such as DC-DC converters [9], [10]. However, these control methods use the information of the coupling coefficient which changes constantly and is not directly measurable. In the paper [11], a method to estimate coupling coefficient and real-time maximum efficiency control were introduced. Yet, the secondary voltage which has maximum efficiency was not tracked well enough because the control of DC-DC converter was just based on static feed forward control. In this paper, an structure of DWPT system optimized for the transmitting efficiency is introduced. Moreover, a simple method of coupling coefficient estimation and a control method of a DC-DC converter based on dynamic feedback control which has better characteristics of tracking the maximum efficiency point than the previous research are proposed. In section II, the proposed DWPT system structure is introduced. In section III, the basic ideas to track maximum efficiency and to estimate coupling coefficient between a transmitter and a receiver are explained. Furthermore, the modeling and the control method of a DC-DC converter for DWPT system are introduced in section IV. Lastly, the simulation results and the experimental results using experimental setup which simulates DWPT for EVs are provided in section V.
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Fig. 4. Model of WPT with the simplified secondary side.
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978-1-4799-1762-4/15/$31.00 ©2015 IEEE
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Fig. 2. Proposed receiving side.
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III. M AXIMUM E FFICIENCY C ONTROL AND R EAL -T IME C OUPLING C OEFFICIENT E STIMATION A. Maximum efficiency control For simplicity, the WPT model that has a constant voltage source and a constant voltage load is targeted. Fig.3 shows the change in the transmitting efficiency at different secondary voltages V2 (RMS value). Fig. 3 shows that the efficiency depends on V2 and has a peak at a certain voltage (V2ηmax ), which is derived as (1) [10]. V2ηmax = R2 R1 √ ω0 k L 1 L 2 R1 R2 + (ω0 k ) L1 L2 +
Daita Kobayashi∗ , Takehiro Imura∗∗ , Yoichi Hori∗∗∗
The University of Tokyo 5-1-5, Kashiwanoha, Kashiwa, Chiba, 277-8561, Japan Phone: +81-4-7136-3881 Email: kobayashi14@hflab.k.u-tokyo.ac.jp∗ , imura@hori.k.u-tokyo.ac.jp∗∗ , hori@k.u-tokyo.ac.jp∗∗∗
IECON2015-Yokohama November 9-12, 2015
Real-time Coupling Coefficient Estimation and Maximum Efficiency Control on Dynamic Wireless Power Transfer Using Secondary DC-DC Converter
Abstract—Transmitting efficiency is able to be controlled by changing the input impedance on the receiving side using a DC-DC converter for static wireless power transfer system. However, the control method has never been applied for dynamic wireless power transfer system where coupling coefficient changes drastically. The information of coupling coefficient is needed constantly to achieve the control. Moreover, the considerations about dynamics of the transmitting circuit and coupling coefficient are necessary in dynamic wireless power transfer system. In this paper, a simple method of coupling coefficient estimation with RLS (Recursive least squares) filter and maximum efficiency control using a PID feedback controller are proposed. The simulation and experimental results of dynamic maximum efficiency control are provided and indicating the effectiveness of the proposed control in a real dynamic wireless power transfer system for EVs.