Wireless charging of the EVs offers a convenient, reliable, and automatic charging of the autonomous vehicles without user interference. The focus of this thesis is the design and optimization of new structures for stationary EV wireless charging applications. The fundamentals of the Wireless Power Transfer (WPT) system and its main components including the magnetic couplers, transmitter and receiver power converters, and control methods are studied in depth. The requirements of the EV wireless charging application and design criteria are discussed in detail. The advantages and disadvantages of each topology are highlighted, and possible candidates for EV wireless charging applications are selected. Optimization of the resonant networks in terms of maximum efficiency and misalignment tolerance is studied. Different resonant topologies are studied in detail and their sensitivity functions are extracted. For each topology, an efficiency model is presented that includes the inverter, resonant capacitors, resonant inductor, diode-bridge, and core and conduction losses. Each topology is optimized with two different objective functions and the results are compared through the simulation and experiments. According to the optimization results, suitable topologies for the EV wireless charging application are selected. In order to increase the power density of the wireless charging system, and save ferrite material, integrated inductors into the magnetic couplers are proposed. In this structure, the DC-DC inductor is integrated into the receiver main coil and the resonant inductor is integrated into the transmitter coil. This integration introduces new challenges to the design of the resonant network and magnetic coupler due to the unwanted cross-coupling effect. To address this issue, the fully integrated magnetic structure is optimally designed to have minimum cross-coupling. Moreover, the resonant network is designed based on an optimization problem that includes the cross-coupling into the system equations to ensure maximum efficiency. The proposed fully-integrated magnetic structure is built and experimental tests are presented to validate the performance of the proposed magnetic structure and its optimization method. To reduce the implementation cost, size and weight a PCB-based magnetic coupler is proposed to replace the Litz wire in the magnetic coupler of the WPT system. Moreover, the proposed PCB-magnetic coupler increases the repeatability of the design and reduces manufacturing errors. The PCB-based magnetic coupler is studied through Finite Element Analysis (FEA) to minimize the AC resistance of the coil. Different parameters such including the number of the PCB layers, copper cross-section, and layer thickness are studied in detail to evaluate their effect on the coil resistance. Thermal analysis is performed to ensure the feasibility of the design under different loading conditions. A 3.3 kW/85 kHz wireless charging system is built and experimental tests are presented. A novel modular resonant topology for fast wireless charging is proposed. A modular structure offers reliability, scalability, and better thermal management. The proposed topology is made by multi-parallel inverter legs connected to an LCC resonant network. The outputs of the resonant networks are connected in parallel to feed the transmitter coil with a high excitation current. The proposed modular system is compared with a conventional system and it showed superior performance in different aspects. / Thesis / Doctor of Philosophy (PhD)

京都大学 / 新制・課程博士 / 博士(工学) / 甲第24232号 / 工博第5060号 / 新制||工||1790(附属図書館) / 京都大学大学院工学研究科電気工学専攻 / (主査)教授 篠原 真毅, 教授 小嶋 浩嗣, 教授 山本 衛 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

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<p> The motor driven treadmill is often used in research as a convenient tool for simulating overground running. There has been varied opinion in the literature regarding the accuracy of this assumption. The major difference that has been quantified is the variation in treadmill belt speed as a result of the forces applied by a runner. In comparison, the earth does not vary its speed during overground running. The aim of the present study was to more clearly define the causes of treadmill belt-speed variation and to elucidate its effects on running mechanics. </p> <p> An in-lab fabricated tachometer was used to determine accurate treadmill belt speed while the treadmill was challenged by five subjects weighing 55.2 to 99.6 kg running at four speeds of 2.6, 3.1, 3.5 and 4.0 m/s. The actual running velocity was found on average to be 0.62% higher than the treadmill display setting. The intra-step belt-speed variation ranged from 4.2 to 8.6 % of average belt velocity. Linear regression analysis showed that 86 % of the variance in intra-step belt-speed variation was attributed to total body mass and a further 10 % attributed to running speed. </p> <p> The effect that this variation had on running mechanics was determined from the power transfer between the foot and belt, as calculated from the product of the change in belt speed and the horizontal ground reaction force. The horizontal force, as calculated using a segmental acceleration approach, did not show complete agreement with simultaneously recorded forceplate data. It was found that an average of 4.49 J flowed to the treadmill during the eccentric phase of running and 3.37 J of energy flowed to the runner during the concentric phase of running. Despite inaccuracies in the calculation, the mathematical approach used in this study permitted insight into the theoretical benefit of belt-speed variation in treadmill running. </p> / Thesis / Candidate in Philosophy

Due to the loose coupling nature and separated primary/secondary side, achieving tight load regulation or implementing closed-loop control of output voltage/current is nontrivial in a wireless power transfer (WPT) system. Previously presented methods for regulating or controlling the output of a WPT system include incorporating either post-regulator stage, wireless communication from secondary to primary side, primary side sensing and modulation scheme, or dual active bridge type of topology. However, all existing methods have limitations and disadvantages in terms of increased size/cost, control complexity, or reliability in electrically noisy environments. This dissertation proposes a single switch control and regulation mechanism based on the secondary side of the WPT system. Specifically, the duty cycle of the secondary side synchronous rectifier (SR) switch is modulated to control the output voltage or current. By modulating the SR duty cycle, output of the WPT system can be controlled without requiring additional regulator stages/power devices, a primary side sensing mechanism, or secondary to primary communication. The proposed control method lowers cost and simplifies the design of WPT systems while improving reliability in noisy environments. The proposed control and modulation mechanism maintains zero voltage switching of all power semiconductor switches so efficiency of the WPT system would not be compromised by implementing the proposed control scheme. The proposed secondary side SR based control method can be applied to dc-dc WPT systems to control output voltage or current, or it could be used in a dc-ac WPT system to generate and regulate ac output if combined with an unfolding stage. When used in dc-ac WPT systems, the bulky output filter stage usually required in conventional dc-ac inverters is eliminated. The proposed control scheme is evaluated with computer simulation as well as hardware implementation and testing. / Doctor of Philosophy / Wireless power transfer (WPT) is an emerging technology that supplies electric power to loads without using wires or electrical contacts. WPT technology has many promising uses in consumer, industrial, transportation, biomedical, and other applications. However, unlike controlling the output voltage of a conventional power supply or power converter, controlling the output of a WPT system is not a simple task due to the physical separation between the transmitting and receiving sides. State-of-the-art methods for controlling the output of a WPT system include adding another power regulator stage to regulate output, incorporating secondary side (power receiver) to primary side (power transmitter) communication so that output information can be passed back to the primary side where that information is used to monitor and regulate output. In some systems, output information may also be estimated indirectly from primary side voltage/current information. However, all these methods have significant disadvantages. Adding another power converter stage increases cost and efficiency loss of the WPT system. Incorporating secondary to primary communication for output control is detrimental to the reliability of the PWT system because communication may be impacted by external noise. The reliability of primary side sensing and regulation is also severely impacted by component parameter variations in the WPT system. This dissertation proposes a new mechanism that controls output of a WPT system at the receiver or secondary side without needing another power conversion stage, communication or any cooperation from primary side. The proposed control mechanism controls the turn on duration of the synchronous rectifier (SR) switch at the receiver side to modulate output voltage or current. Since SR technology is already prevalently used in power electronics systems, including WPT systems, to efficiently convert high frequency ac to dc before delivering power to the load, implementing the proposed control mechanism does not increase complexity or cost of the WPT system. The proposed control mechanism is useful in both dc-dc and dc-ac WPT systems. In a dc-dc WPT system, the proposed mechanism can control or regulate output voltage or current independently from the primary side, while in a dc-ac WPT system the proposed mechanism can generate and regulate ac output. If used in a dc-ac WPT system an unfolding stage needs to be added, but the bulky output filter stage required in conventional pulse width modulation (PWM) dc-ac inverters for suppressing switching ripple is not needed. The proposed mechanism is verified with computer simulation as well as hardware prototyping in this dissertation.

Recentemente os sistemas de transferência de energia sem fio WPT (do inglês Wireless Power Transfer) têm sido amplamente estudados com o propósito de alimentar eficientemente diversos tipos de cargas através de técnicas específicas, dentre elas destaca-se a transferência capacitiva de potência CPT (do inglês Capacitive Power Transfer) e a transferência indutiva de potência IPT (do inglês Inductive Power Transfer), sendo esta última objeto deste estudo. Em um sistema de transferência indutiva de potência a carga é alimentada através de um transformador fracamente acoplado. Em função do elevado espaçamento entre as bobinas primária e secundária, da ausência de núcleo magnético, ou o emprego do núcleos divididos e separados por um grande entreferro, o transformador apresenta alta reatância de dispersão e baixa reatância de magnetização, o que resulta em elevadas correntes, baixa eficiência e regulação da tensão ruim quando houver variação da carga. Com o intuito de aumentar a eficiência e melhorar a regulação de tensão (ou corrente) são aplicadas compensações capacitivas em ambos os lados do transformador, elevando o número de elementos reativos, o que dificulta a compreensão do seu comportamento. Adicionalmente, as diversas configurações geométricas possíveis para a construção das bobinas dificultam a otimização do projeto de transferência indutiva de potência. Esta dissertação analisa e compara as estratégias de compensação série-série (SS) e série-paralela (SP) sob diversos pontos de vista, identificando pontos de operação relevantes nos quais o sistema atua como uma fonte de corrente ou de tensão em malha aberta, modela os elementos que constituem um sistema de transferência indutiva de potência para alcançar à eficiência requisitada. Adicionalmente este trabalho lista os impactos na fonte e na carga quando do desvio das condições nominais de operação e dá diretrizes que permitem escolher os elementos de um sistema IPT. Na sequência esta dissertação propõe as diretrizes para a construção do transformador com valores predefinidos de fator de qualidade, indutâncias próprias e fator de acoplamento. Por fim, o presente trabalho dimensiona e confecciona alguns sistemas IPT a partir de uma lista de especificações, usando uma metodologia de projeto baseada em fórmulas aproximadas e a valida experimentalmente. / Recently Wireless Power Transfer (WPT) is widely studied in order to efficiently feed many different kinds of loads using specific techniques, such as Capacitive Power Transfer (CPT) and Inductive Power Transfer (IPT). IPT system relies on large air gap and loosely coupled transformer which will be studied in this work. Due to the large separation between the primary and secondary coils, the absence of a magnetic core, or the presence of split cores the transformer presents large leakage inductances, resulting in poor voltage regulation against load variation. Moreover, the low magnetizing inductance results in high magnetizing currents, reducing the overall efficiency. In order to improve the WPT performance, capacitive compensation techniques are applied in both sides of the transformer. Series compensation is commonly used at the primary side of the WPT transformer while Series or Parallel compensation is eligible to the secondary side. In addition, the loosely coupled transformer must be designed, in spite of the complex relationship between the various electrical and geometrical parameters of the coils that complicates the transformer construction and its optimization. This work compares Series-Series and Series-Parallel compensation strategies based on a simple approach, comprehensively highlighting the pro and cons of each one. Also the open loop operation in voltage source and current source modes, and the effect of the gap length for both compensation strategies are discussed. Moreover, the elements that constitute an inductive power transfer system are modeled in order to achieve the required efficiency. This research also proposes some guidance to build the transformer with high figure-of-merit and coupling. Finally, the present work designs and builds few IPT systems that satisfies a set of specifications, based on a simplified design procedure. The proposed design methodology is experimentally validated.

Recentemente os sistemas de transferência de energia sem fio WPT (do inglês Wireless Power Transfer) têm sido amplamente estudados com o propósito de alimentar eficientemente diversos tipos de cargas através de técnicas específicas, dentre elas destaca-se a transferência capacitiva de potência CPT (do inglês Capacitive Power Transfer) e a transferência indutiva de potência IPT (do inglês Inductive Power Transfer), sendo esta última objeto deste estudo. Em um sistema de transferência indutiva de potência a carga é alimentada através de um transformador fracamente acoplado. Em função do elevado espaçamento entre as bobinas primária e secundária, da ausência de núcleo magnético, ou o emprego do núcleos divididos e separados por um grande entreferro, o transformador apresenta alta reatância de dispersão e baixa reatância de magnetização, o que resulta em elevadas correntes, baixa eficiência e regulação da tensão ruim quando houver variação da carga. Com o intuito de aumentar a eficiência e melhorar a regulação de tensão (ou corrente) são aplicadas compensações capacitivas em ambos os lados do transformador, elevando o número de elementos reativos, o que dificulta a compreensão do seu comportamento. Adicionalmente, as diversas configurações geométricas possíveis para a construção das bobinas dificultam a otimização do projeto de transferência indutiva de potência. Esta dissertação analisa e compara as estratégias de compensação série-série (SS) e série-paralela (SP) sob diversos pontos de vista, identificando pontos de operação relevantes nos quais o sistema atua como uma fonte de corrente ou de tensão em malha aberta, modela os elementos que constituem um sistema de transferência indutiva de potência para alcançar à eficiência requisitada. Adicionalmente este trabalho lista os impactos na fonte e na carga quando do desvio das condições nominais de operação e dá diretrizes que permitem escolher os elementos de um sistema IPT. Na sequência esta dissertação propõe as diretrizes para a construção do transformador com valores predefinidos de fator de qualidade, indutâncias próprias e fator de acoplamento. Por fim, o presente trabalho dimensiona e confecciona alguns sistemas IPT a partir de uma lista de especificações, usando uma metodologia de projeto baseada em fórmulas aproximadas e a valida experimentalmente. / Recently Wireless Power Transfer (WPT) is widely studied in order to efficiently feed many different kinds of loads using specific techniques, such as Capacitive Power Transfer (CPT) and Inductive Power Transfer (IPT). IPT system relies on large air gap and loosely coupled transformer which will be studied in this work. Due to the large separation between the primary and secondary coils, the absence of a magnetic core, or the presence of split cores the transformer presents large leakage inductances, resulting in poor voltage regulation against load variation. Moreover, the low magnetizing inductance results in high magnetizing currents, reducing the overall efficiency. In order to improve the WPT performance, capacitive compensation techniques are applied in both sides of the transformer. Series compensation is commonly used at the primary side of the WPT transformer while Series or Parallel compensation is eligible to the secondary side. In addition, the loosely coupled transformer must be designed, in spite of the complex relationship between the various electrical and geometrical parameters of the coils that complicates the transformer construction and its optimization. This work compares Series-Series and Series-Parallel compensation strategies based on a simple approach, comprehensively highlighting the pro and cons of each one. Also the open loop operation in voltage source and current source modes, and the effect of the gap length for both compensation strategies are discussed. Moreover, the elements that constitute an inductive power transfer system are modeled in order to achieve the required efficiency. This research also proposes some guidance to build the transformer with high figure-of-merit and coupling. Finally, the present work designs and builds few IPT systems that satisfies a set of specifications, based on a simplified design procedure. The proposed design methodology is experimentally validated.

Contactless Electric Vehicle (EV) charging based on magnetic resonant induction is an emerging technology that can revolutionize the future of the EV industry and transportation systems by enabling an automated and convenient charging process. However, in order to make this technology an acceptable alternative for conventional plug-in charging systems it needs to be optimized for different design measures. Specifically, the efficiency of an inductive EV charging system is of a great importance and should be comparable to the efficiency of conventional plug-in EV chargers. The aim of this study is to develop solutions that contribute to the design enhancement of inductive EV charging systems. Specifically, generalized physics-based design optimization methods that address the trade-off problem between several key objectives including efficiency, power density, misalignment tolerance, and cost efficiency considering critical constraints are developed. Using the developed design methodology, a 3.7kW inductive charging system with square magnetic structures is investigated as a case study and a prototype is built to validate the optimization results. The developed prototype achieves 93.65% efficiency (DC-to-DC) and a power density of 1.65kW/dm3. Also, self-tuning power transfer control methods with resonance frequency tracking capability and bidirectional power transfer control are presented. The proposed control methods enhance the efficiency of power converters and reduce the Electromagnetic Interference (EMI) by enabling soft-switching operations. Several simplified digital controllers are developed and experimentally implemented. The controllers are implemented without the use of DSP/FPGA solutions. Experimental tests show that of the developed simplified controllers can effectively regulate the power transfer around the desired value. Moreover, the experiments show that compared to conventional converters, the developed converters can achieve 4% higher efficiency at low power levels. Moreover, enhanced matrix converter topologies that can achieve bidirectional power transfer and high efficiency with a reduced number of switching elements are introduced. The self-tuning controllers are utilized to design and develop control schemes for bidirectional power transfer regulation. The simulation analyses and experimental results show that the developed matrix converters can effectively establish bidirectional power transfer at the desired power levels with soft-switching operations and resonance frequency tracking capability. Specifically, a direct three-phase AC-AC matrix converter with a reduced number of switches (only seven) is developed and built. It is shown that the developed converters can achieve efficiencies as high as 98.54% at high power levels and outperform conventional two-stage converters.

In the era of Internet of things (IoT), sensor-equipped devices exchange data over networks. In battery powered IoT devices, the lifespan of the devices is often much longer than the battery life, leading to multiple costly and environmentally hazardous battery replacements during the operational life of the devices. As a result, there is a growing interest in using rechargeable batteries that can be wirelessly fast charged to prolong the lifespan of IoT devices and their batteries. In wireless power transfer based on induction, the transmitter and receiver antennas can be accurately modeled as two coils in separate circuits. The transmitter coil, energized by alternating current, generates an oscillating magnetic field that induces an electric field in the nearby receiver coil, following Faraday's law of induction. By connecting a resistive load to the receiver coil, it is then possible to extract energy from the induced electric field. This project investigates inductive fast charging for IoT devices with a focus on the electromagnetic power transfer. Two different types of coil antennas were simulated in a solver based on the finite element method and tested in lab for verification purpose. One was a transformer-like ETD coil and the other a flat spiral coil. Both the transmitter and receiver coils were compensated with a capacitor in series to allow for increased efficiency and power transfer at the designated frequency of 100 kHz. The compensating capacitors were tuned such that frequency bifurcation or frequency splitting was avoided. Due to the higher quality factor of the ETD coil compared to the spiral coil they were compensated differently to operate at the resonance peak. The simulation and the experimental tests agreed well, and the findings indicate that both types of coils demonstrate the ability to transfer high power with high efficiency. Theoretically there is no limit in the power transfer for both types of coils since it is proportional to the square of the excitation voltage. All tested coils exhibited the ability to transfer a power of at least 30 W with an 86 to 92 % efficiency without experiencing any significant temperature elevation. The advantages of each coil depend on the design of the systems surrounding the power transfer unit and the nature of the built charging system. For scenarios where the equivalent load resistance of the battery charger unit on the receiver remains relatively constant throughout the charging process, the spiral coil proves to be a suitable choice due to its inherent capacity for easy dimensioning, allowing optimal efficiency for a specific load resistance. Conversely, if the equivalent load resistance fluctuates significantly during the charging process, the ETD coil would be a better alternative, since it exhibits small load dependence and high efficiency. Finally, to further increase the validity of the simulation model, the full magnetization curve of the ferrite core and a more general core loss model should be implemented to enhance the accuracy in studying the effects of higher harmonics and when operating closer to saturation.