路 面 供 电 电 动 汽 车 感 应 电 能 传 输 系 统 综 述. A Review on Inductive Power Transfer Systems for Roadway Powered Electric Vehicles

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1 2013 年 电 工 技 术 学 报 Vol.28 Sup.2 第 28 卷 增 刊 2 TRANSACTIONS OF CHINA ELECTROTECHNICAL SOCIETY 2013 路 面 供 电 电 动 汽 车 感 应 电 能 传 输 系 统 综 述 田 勇 1, 夏 必 忠 1*, 徐 智 慧 2, 孙 威 2, 郑 伟 伟 (1. 清 华 大 学 深 圳 研 究 生 院 深 圳 欣 旺 达 电 子 股 份 有 限 公 司 深 圳 ) 2 摘 要 近 年 来, 由 于 化 石 燃 料 的 日 益 紧 缺 以 及 自 然 环 境 的 不 断 恶 化, 电 动 汽 车 受 到 了 人 们 的 广 泛 关 注 然 而, 其 发 展 和 商 业 化 进 程 受 到 了 诸 如 价 格 高 昂 电 池 组 庞 大 笨 重 续 航 里 程 短 充 电 时 间 长 以 及 充 电 频 繁 等 因 素 的 严 重 阻 碍 为 了 解 决 上 述 问 题, 人 们 提 出 了 基 于 感 应 电 能 传 输 技 术 的 路 面 供 电 电 动 汽 车 ( 或 称 为 在 线 电 动 汽 车 ) 本 文 从 供 电 导 轨 和 拾 取 机 构 谐 振 变 换 器 和 控 制 策 略 电 磁 屏 蔽 技 术 等 几 个 方 面 综 述 了 感 应 电 能 传 输 系 统 在 路 面 供 电 电 动 汽 车 领 域 的 应 用 现 状 此 外, 并 就 应 用 于 路 面 供 电 电 动 汽 车 感 应 电 能 传 输 系 统 未 来 可 能 的 发 展 趋 势 做 了 探 讨 关 键 词 : 感 应 电 能 传 输 路 面 供 电 电 动 汽 车 供 电 导 轨 电 磁 场 屏 蔽 中 图 分 类 号 :TM72 A Review on Inductive Power Transfer Systems for Roadway Powered Electric Vehicles Tian Yong 1, Xia Bizhong 1*, Xu Zhihui 2, Sun Wei 2, Zheng Weiwei 2 (1. Graduate School at Shenzhen Tsinghua University Shenzhen China 2. Sunwoda Electronic Co., Ltd. Shenzhen China) Abstract In recent years, electric vehicles (EVs) are widely concerned due to fossil fuel shortage and environmental deterioration. However, their development and commercialization are obstructed by significant drawbacks, such as the high price, overweight of battery pack, short driving distance, long charging time and frequent charging requirement, etc. To solve these problems, the so-called roadway powered electric vehicles (RPEVs) or online electric vehicles (OLEVs) using an inductive power transfer (IPT) technique have been proposed. This paper presents the recent research adva ncements of IPT systems for RPEVs (IPTS-RPEVs) application, including the power track and pick-up, resonant converter and control strategy, and electromagnetic field shielding methods. Moreover, the possible future trends of IPTS-RPEVs are also been discussed. Keywords: Inductive power transfer, roadway powered electric vehicles, power track, electro - magnetic filed shielding 1 Introduction The green vehicles, such as pure electric vehicle (PEV), hybrid electric vehicle(hev) and fuel cell electric vehicle(fcev), etc. are the global trend in the automobile industry. Among of them, the pure electric vehicle is considered as the most prospective one, which is the most suitable alternative of the internal combustion engines(ice) vehicles powered by petroleum. However, its development and commercialization are obstructed by some obvious drawbacks, such as the high price, heaviness, and the large space required by battery pack. In addition, the shorter driving range than ICE vehicles, long charging time, frequent charging requirements and the lack of charging infrastructure are not ignorable. In order to resolve these problems, the RPEVs using an wireless power transfer(wpt) technology were developed [1-5]. As one of the WPT methods,

2 76 电 工 技 术 学 报 2013 年 inductive power transfer (IPT) technique has become a hot research area and is the relatively mature one until now. The IPT system for RPEVs mainly employs inductive coupling, replacing wires and connectors to transmit electric energy from power source to EVs. This paper presents the fundamental structure and working process of IPTS-RPEVs, and also reviews the current research and development situations of IPT technology used in RPEVs. 2 Inductive power transfer system for rpevs A typical IPT system for RPEVs consists of primary power converter, the underground power tracks, the on-board pickups and the on-board power converter as shown in Fig.1, which depicts the process how an EV gets energy when it is moving along the road with a power track installed. Firstly, primary power converter takes electric energy from a conventional single-phase or three-phase power source to generate a high frequency sinusoidal current in the primary sub-track (L p ), around which high frequency magnetic field is formed. Then, in the on-board pick-up (L s ) located in the high frequency magnetic field, high frequency current is induced and finally conditioned by the on-board converter and filter to produce stable electrical supply to battery charging or motor drivin. Fig.1 Structure of IPTS-RPEVs Project supported by China Postdoctoral Science Foundation(2013M )and Shenzhen Key Laboratory of LED Packaging (NZDSY ).*Xia Bizhong is the corresponding author Received May 23, The Development of ipts for rpevs 3.1 Power track and pick-up In the RPEVs system, energy needs to be transferred over relatively large air gaps while allowing sufficient lateral/vertical misalignment tolerance to guarantee free driving. The design of the power track is critical to meet these demands. A excellently designed power track should be such that ensures the loss, cost and EMF (electromagnetic field) are minimised while maximising horizontal and ver- tical misalignment tolerance. In the traditional single-phase IPT systems, the magnitude of the magnetic field drops rapidly as the lateral misalignment distance between the pickup and the track increases [6]. As a result, bulky pickups or a vehicle guidance system are required to keep the required tolerance to lateral movement. However, neither of these is desirable for a passenger vehicle which is driven by a human and sensitive to heaviness of the pick-ups. In order to solve aforementioned problems, several track layouts, such as single-layer [7] or multilayer [8] honeycomb track, three-phase track [9] as shown in Fig.2 have been proposed. However, all of these layouts result in significant track cable requirements and high standing losses. Consequently, a simple, low cost two-phase track and power supply system as shown in Fig.3 is proposed in Ref. [6]. This system can provide similar benefits to a more complex threephase system while lowering the system cost with a simpler installation. Meanwhile, a quadrature pick-up, providing additional benefits in maintaining a constant power transfer across the width of the roadway is

3 第 28 卷 增 刊 2 田 勇 等 路 面 供 电 电 动 汽 车 感 应 电 能 传 输 系 统 综 述 77 proposed. When used together, they can provide the vehicle with high movement freedom and a low total system cost [6]. width of 10 cm, a small pickup size of 80cm, a large air gap of 20cm and alternating polarity magnetic poles along the road. Each magnetic pole consists of a I-type ferrite core and turned cables. The EMF around the power track can be drastically reduced due to the EMF cancellation by neighborhood poles with the opposite polarity. As the pick-up is much wider Fig.2 Three phase IPT system Fig.3 Two phase IPT system A sectional tracks for RPEVs shown in Fig.4 is proposed in Ref. [10]. Each track can be individually switched on or off based on the number of vehicles within the range. It indicates that the different sectional tracks can be allocated to different microgrid Fig.4 Sectional track system units (wind, solar, etc. ) to improve system efficiency and reliability. An IPT system for OLEVs shown in Fig.5 is proposed in Ref. [11]. It consists of a narrow rail Fig.5 I-type power track and pick-up than the power track, large lateral misalignment tolerance can also be achieved. Meanwhile, an experimental prototype is developed and the results indicate that the maximum output power is 35kW and the maximum efficiency is 74% at 27kW. To minimize the EMF generated by power track and allow the system to drive multiple RPEVs at a time, a new cross-segmented power supply rail named as X-rail is proposed in Ref. [12]. Each sub-rail is connected with an auto-compensation switch box which consists of four sets of bidirectional power switches, four compensation capacitors and a transformer. The auto-compensation switch box is able to change the current direction of a pair of power cables as shown in Fig.6. With such X-rail and an inverter, several RPEVs can be selectively driven and the cost can be effectively lowered by reducing the used power cable.

4 2013 年 电 工 技 术 学 报 Vol.28 Sup.2 第 28 卷 增 刊 2 TRANSACTIONS OF CHINA ELECTROTECHNICAL SOCIETY 2013 Fig.6 The circuit configuration and current direction of the X-rail for different switch connections 3.2 Resonant converter and control strategy In order to maximize the magnetic field strength and minimize the VA (volt-ampere) rating of the power source, the resonant converter is usually employed in the IPT systems. A novel resonant topology named as SPS topology, which combines the characteristics of SS (Series- Series) and PS (Parallel-Series) configurations is proposed in Ref. [13]. This topology may transfer rated power with high lateral misalignment (up to 25% for a 2kW laboratory-scale prototype) of the pick-up width without a specific controller and with high efficiency. Therefore, it indicates that a suitable compensation topology can be used as a new method to improve lateral misalignment tolerance for RPEVs. For the segmented or sectional tracks application, a dual-powered track structure and a topology used to implement this structure are proposed in Ref. [14]. With two inverters in this topology, more control freedom can be achieved. Meanwhile, the ACM-DDC (Asymmetrical Clamped Mode- Different Duty Cycle) control strategy is considered as the best choice. A full-resonant converter, which shows quite different characteristics compared with conventional converters, is proposed in Ref. [15]. In this converter, a current source is used at the primary side, and the system is fully resonated to maximize power transfer. It is quite robust to the load change or power source fluctuation. Furthermore, the output voltage of this converter is nearly constant regardless of output power, and the output current may increase regardless of source current. 3.3 Electromagnetic filed shielding According to the International Committee on Non-Ionizing Radiation Protection (ICNIRP), in the frequency range (usually 10~150kHz) of IPT systems, a maximum of 6.25μT or 62.5mG is allowed to be exposed to the body. As a magnetic flux more than hundreds of mg from current of thousands of ampereturn is generated between power track and pick-up, even 0.1% of leakage from main flux can be hundreds of mg [16]. Therefore, it is very necessary to minish the leakage magnetic flux in the IPT system for RPEVs. For the reduction of EMF from the power tracks and RPEVs themselves, some electromagnetic filed shielding methods have been proposed. Passi ve metallic plate shield and active shield methods shown in Fig.7 are proposed to minimize the leakage EMF from the IPT system for OLEVs [16]. And the test results show that the EMF level is lower than 62.5 mg at the observation points. A 5 kw pad meets the ICNIRP regulations at a distance of 900 mm from the center, which is sufficient due to the extended width of the car chassis [17]. By applying a metallic plate shield, horizontal and vertical shield, and connecting (a)passive shield

5 第 28 卷 增 刊 2 田 勇 等 路 面 供 电 电 动 汽 车 感 应 电 能 传 输 系 统 综 述 79 have become a hotspot in the automobile industry. This paper has reviewed the current research state and discussed the future trend of the IPT systems for RPEVs. This new technology will be preferentially applied in the public transportation due to its fixed travelling path and lower sensibility to the cost. References (b)active shield Fig.7 Passive and active shielding methods wire for loop cancellation, the low frequency EMF is significantly reduced to less than 62.5mG at the observation points [18]. 4 Future trends of ipts-rpevs IPT systems for RPEVs have steadily gained in popularity over recent years as it reduces the total amount of on-board battery packs, extends the driving range, shortens the charging time and saves the construction land of charging stations. Segmented tracks will acquire great development because it increases the system efficiency. In order to improve the lateral misalignment tolerance and reduce the total length of track requirements, however, much deeper research should focus on the efficient and low-cost power tracks structure, and intelligent control strategy for each single track segment. The optimization design of the resonant converter in the IPTS-RPEVs is another challenging work due to the dynamic and static behaviors of the system in practice. The IPTS- RPEVs, the same as the EVs themselves, will be firstly applied in the public transportation, such as the bus, taxi, AGV (automatic guide vehicle), and mono rail which have the lower sensibility to the cost than the private one and have the relatively fixed travelling path. 5 Conclusions The limited fossil fuel and worsening environment have allowed EVs to greatly develop over the past decades. However, they have not been widely popular due to some drawbacks resulted by battery technology. Because of their advantages in expanding driving range, reducing battery weight and saving recharge time, the RPEVS using an IPT technique [1] Zhu C B, Liu K, Yu C L, et al. Simulation and Experimental Analysis on Wireless Energy Transfer Based on Magnetic Resonances, Vehicle Power and Propulsion Conference, US, IEEE, 2008: 1-4. [2] Zou Y W, Huang X L, Tan L L, et al. Current Research Situation and Developing Tendency about Wireless Power Transmission, International Conference on Electrical and Control Engineering, US, IEEE, 2010: [3] Wu H H, Gilchrist A, Sealy K, et al. A Review on Inductive Charging for Electric Vehicles, International Electric Machines & Drives Conference, US, IEEE, 2011: [4] Zhang X, Yang Q X, Chen H Y, et al. Modeling and Design and Experimental Verification of Contactless Power Transmission Systems via Electromagnetic Resonant Coupling[J]. Proceeding of the CSEE, 2012: [5] Tian Y, Sun Y, Su Y G, et al. Neural Network -based Constant Current Control of Dynamic Wireless Power Supply System for Electric Vehicles, Information Technology Journal, Pakistan, ITJ, 2012: [6] Kissin M L G, Hao H and Covic G A. A practical Multiphase IPT System for AGV and Roadway Applications[C]. Energy Conversion Congress and Exposition, US, 2010: [7] Achterberg J, Lomonova E A, De Boeij J. Coil Array Structures Compared for Contactless Battery Charging Platform[J]. IEEE Transactions on Magnetics, 2008: [8] Liu X, Hui S Y R. Equivalent Circuit Modeling of a Multilayer Planar Winding Array Structure for Use in a Universal Contactless Battery Charging Platform [J]. IEEE Transactions on Power Electronics, 2007: [9] Covic G A, Boys J T, Kissin M L G, et al. A

6 80 电 工 技 术 学 报 2013 年 Three-Phase Inductive Power Transfer System for Roadway-Powered Vehicles[J]. IEEE Transactions on Industrial Electronics, 2007, 54(6): [10] Zhang W, Wong S C, Tse C K, et al. A Study of Sectional Tracks in Roadway Inductive Power Transfer System[C]. ECCE: Energy Conversion Innovation for a Clean Energy Future, US, IEEE, 2011: [11] Huh J, Lee S W, Lee W Y, et al. Narrow-Width Inductive Power Transfer System for Online Electrical Vehicles, IEEE Transactions on Power Electronics, U S, I E E E, , 2 6 ( 1 2 ) : [12] Huh J, Lee W Y, Choi S Y, et al. A New Cross- Segmented Power Supply Rail for Roadway Powered Electric Vehicles[C]. International Sympo- sium on Power Electronics for Distributed Generation Systems, US, IEEE, 2011: [13] Villa J L, Sallán J, Osorio J F S, et al. High- Misalignment Tolerant Compensation Topology for ICPT Systems[J]. IEEE Transactions on Industrial Electronics, 2012: [14] Bai S Z, Pantic Z, Lukic S. Dual-Powered Track Sections for Roadway Powered Electric Vehicles[C]. Vehicle Power and Propulsion Conference, US, IEEE, 2011: 1-6. [15] Huh J, Lee W Y, Cho G H, et al. Characterization of Novel Inductive Power Transfer Systems for On-Line Electric Vehicles[C]. Applied Power Electronics Conference and Exposition, US, IEEE, 2011: [16] Ahn S Y and Kim J. Magnetic Field Design for High Efficient and Low EMF Wireless Power Transfer in On-Line Electric Vehicle[C]. Proceedings of the 5th European Conference on Antennas and Propagation, 2011: [17] Budhia M, Covic G A, Boys J T. Design and Optimisation of Magnetic Structures for Lumped Inductive Power Transfer Systems[C]. Energy Conversion Congress and Exposition, 2009: [18] Ahn S Y, Pak J, Song T, et al. Low Frequency Electromagnetic Field Reduction Techniques for the On-Line Electric Vehicle (OLEV)[C]. International Symposium on Electromagnetic Compatibility, 2010: Brief notes:tian Yong Male, born in 1985, Ph. D degree. His research interests are wireless power transfer systems for electric vehicles, battery management system.*xia Bizhong Male, born in 1969, M.S. degree. He is currently researching the Application of Li-ion Battery Pack, Preparation of Nanostructured Materials.

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