Improving energy capture and power quality of power electronic connected generation

Power electronic converter is a significant intermediate media for electric renewable energy systems when integrated into the utility grid. Renewable energy systems such as wind, solar and wave energy systems usually operate with irregular natural energy sources. Advanced energy conversion interfaces are therefore highly desirable for stable power supply, good system reliability and high energy extraction efficiency. This thesis investigates the power generation and conversion systems, with the concentrations on the long-term operation cost, full-power-range efficiency and power quality of power electronic converters, for wind, solar and wave energy applications. The story starts with a hybrid wind-solar energy system design targeting at improving energy yield and system reliability. Wind energy and solar energy, as two complementary energy resources, are combined in a single energy system that features improved energy supply stability and reduced energy storage requirement. Special adaptive energy extraction maximisation algorithms are developed for energy generators in order to increase the energy extraction efficiency. The overall energy cogeneration system can offer high productivity and robustness under varying weather conditions. In the second part of this thesis, a bidirectional DC-AC converter based on the well-established Silicon (Si) based two-level circuit and the emerging Silicon Carbide (SiC) based three-level circuit is investigated, with the motivation to enhance the full-power-range efficiency in renewable energy generation and conversion systems. The SiC based circuit is advantageous especially under low-power conditions due to its low switching losses. The costs of power electronics, especially the power semiconductor devices, are taken into account. The Si based circuit provides a more cost-effective option and lower conduction losses under high-power conditions to further improve the overall energy conversion efficiency. All these benefits are integrated in a single converter called hybrid level-matching (HLM) converter, which is comprised of parallel-connected SiC and Si based circuits. A model predictive control (MPC) algorithm is developed to assist the switching state selection for minimised power losses across the full power range. The proposed HLM converter shows similar power control quality and better full-power-range efficiency compared to its conventional counterparts. The operation of the HLM converter under the proposed MPC controller is experimentally verified by a lab-scale demonstrator. The final part of this thesis focuses on the control of an existing flying capacitor based multilevel converter known as stacked multicell converter (SMC). Considered as a superior DC-AC converter candidate in renewable energy standalone load applications, SMC can be controlled under different capacitor voltage ratios to increase the output voltage resolution. This is studied to explore the potential to improve power control quality within the same SMC circuit by applying different capacitor voltage set-points. The capacitor voltage balancing and the basic three-phase current control are achieved by means of a space vector based MPC algorithm. A method to reduce the computational burden by shrinking the space vector candidate size is proposed. The trade-off between capacitor voltage balancing and current reference tracking poses a major challenge to the SMC in its flexibility in capacitor voltage ratio choice. This is investigated in detail to verify the feasibility to reduce load harmonic distortion by modifying the traditional capacitor voltage ratio in a SMC with three stacked cells

Feature Papers in Electronic Materials Section

This book entitled "Feature Papers in Electronic Materials Section" is a collection of selected papers recently published on the journal Materials, focusing on the latest advances in electronic materials and devices in different fields (e.g., power- and high-frequency electronics, optoelectronic devices, detectors, etc.). In the first part of the book, many articles are dedicated to wide band gap semiconductors (e.g., SiC, GaN, Ga2O3, diamond), focusing on the current relevant materials and devices technology issues. The second part of the book is a miscellaneous of other electronics materials for various applications, including two-dimensional materials for optoelectronic and high-frequency devices. Finally, some recent advances in materials and flexible sensors for bioelectronics and medical applications are presented at the end of the book

Two-Dimensional Electronic Materials and Devices: Opportunities and Challenges

The unprecedented growth of the Internet of Things (IoT) and the 4th Industrial Revolution (Industry 4.0) not only demands dimensional scaling of device technologies but also new types of applications beyond today’s electronics. Two-dimensional (2D) materials, a group of layered crystals (such as graphene and MoS2) with unique properties, have emerged as promising candidates for IoT and Industry 4.0 since they can, not only extend the scaling with unprecedented performance and energy efficiency but also exhibit high potential for novel electronic devices. However, such nanomaterials suffer from significant challenges in process integration, especially in the modules that involves the formation of interfaces between 2D materials and conventional bulk materials. Thus, realizing high-performance energy-efficient 2D electronic devices has been challenging. This dissertation focuses on understanding the fundamental issues in such 2D materials (such as contacts, interfaces and doping) and in identifying applications uniquely enabled by these materials.First, a comprehensive treatment of metal contacts to 2D semiconductors, which has been a huge hurdle for 2D electronic technologies, will be presented. As a pioneering study, new interface physics originating from the unique dimensionality and surface properties have been revealed [1]. Solutions to minimize contact resistance are described though techniques of interface hybridization [2] and seamless contacts [3], [4]. These techniques transform 2D semiconductors from solely scientifically-interesting materials into high-performance field-effect transistor (FET) technologies, such as MoS2 FETs with record-low contact resistances [5], [6] and WSe2 FETs with record-high drive current and mobility [7]. Beyond metal interfaces, dielectric interface is crucial for preserving the carrier mobility in 2D channels, for which a solution enabled by buffer layers has been proposed [8]. On the other hand, the vertical van der Waals interfaces between 2D and 3D semiconductors, which retain the advantages of pristine ultra-thin 2D films as well as maximized tunneling area/field, have been studied and exploited into a novel beyond-silicon transistor technology – the first 2D channel tunnel FET (TFET) [9], which beat the fundamental limitation in the switching behavior of transistors. Recent results from the engineering of such 2D-3D semiconductor interfaces by surface reduction/passivation are described, showing a significant boost of drive current. While conventional diffusion/ion implantation methods are infeasible for 2D materials, two efficient doping techniques that are specific for 2D materials – surface doping [10], [11] and intercalation doping [12] are presented. The theoretical study of surface doping using ab-initio methods helped develop a novel doping scheme that uniquely exploits the Lewis-base like pedigree of 2D semiconductors without disturbing the structural integrity of the 2D atomic layer configuration [13], as well as a novel electrocatalyst based on MoS2 that achieved record high hydrogen evolution reaction (HER) performance [14]. On the other hand, intercalation doping has been employed to demonstrate graphene based transparent electrodes with the best combination of transmittance and sheet resistance [12], and also the first graphene interconnects with excellent performance, reliability and energy-efficiency [15], [16]. Moreover, by uniquely exploiting the high kinetic inductance and conductivity of intercalation doped graphene, a fundamentally different on-chip inductor has been demonstrated [17], [18], with both small form-factors and high inductance values, that were once thought unachievable in tandem. This 2D technique provides an attractive solution to the longstanding scaling problem of analog/radio-frequency electronics and opens up an unconventional pathway for the development of future ultra-compact wireless communication systems. Finally, a novel dissipative quantum transport methodology based on Büttiker probes with band-to-band tunneling capability is developed for 2D FETs [19]. Subsequently, gate-induced-drain-leakage (GIDL), one of the main leakage mechanisms in FETs especially access transistors, is evaluated for the first time for 2D FETs. The results establish the advantages of certain 2D semiconductors in greatly reducing GIDL and thereby support use of such materials in future memory technologies.The dissertation concludes with a vision for how a smart life can be realized in the future by harnessing the capabilities of various 2D technologies in the era of IoT and Industry 4.0.[1] J. Kang, D. Sarkar, W. Liu, D. Jena, and K. Banerjee, “A computational study of metal-contacts to beyond-graphene 2D semiconductor materials,” in IEEE International Electron Devices Meeting, 2012, pp. 407–410.[2] J. Kang, W. Liu, D. Sarkar, D. Jena, and K. Banerjee, “Computational Study of Metal Contacts to Monolayer Transition-Metal Dichalcogenide Semiconductors,” Phys. Rev. X, vol. 4, no. 3, p. 31005, Jul. 2014.[3] J. Kang, D. Sarkar, Y. Khatami, and K. Banerjee, “Proposal for all-graphene monolithic logic circuits,” Appl. Phys. Lett., vol. 103, no. 8, p. 83113, 2013.[4] A. Allain, J. Kang, K. Banerjee, and A. Kis, “Electrical contacts to two-dimensional semiconductors,” Nat. Mater., vol. 14, no. 12, pp. 1195–1205, 2015.[5] W. Liu et al., “High-performance few-layer-MoS2 field-effect-transistor with record low contact-resistance,” in IEEE International Electron Devices Meeting, 2013, pp. 499–502.[6] J. Kang, W. Liu, and K. Banerjee, “High-performance MoS2 transistors with low-resistance molybdenum contacts,” Appl. Phys. Lett., vol. 104, no. 9, p. 93106, Mar. 2014.[7] W. Liu, J. Kang, D. Sarkar, Y. Khatami, D. Jena, and K. Banerjee, “Role of metal contacts in designing high-performance monolayer n-type WSe2 field effect transistors.,” Nano Lett., vol. 13, no. 5, pp. 1983–90, May 2013.[8] J. Kang, W. Liu, and K. Banerjee, “Computational Study of Interfaces between 2D MoS2 and Surroundings,” in 45th IEEE Semiconductor Interface Specialists Conference, 2014.[9] D. Sarkar et al., “A subthermionic tunnel field-effect transistor with an atomically thin channel,” Nature, vol. 526, no. 7571, pp. 91–95, Sep. 2015.[10] Y. Khatami, W. Liu, J. Kang, and K. Banerjee, “Prospects of graphene electrodes in photovoltaics,” in Proceedings of SPIE, 2013, vol. 8824, p. 88240T–88240T–6.[11] D. Sarkar et al., “Functionalization of Transition Metal Dichalcogenides with Metallic Nanoparticles: Implications for Doping and Gas-Sensing,” Nano Lett., vol. 15, no. 5, pp. 2852–2862, May 2015.[12] W. Liu, J. Kang, and K. Banerjee, “Characterization of FeCl3 intercalation doped CVD few-layer graphene,” IEEE Electron Device Lett., vol. 37, no. 9, pp. 1246–1249, Sep. 2016.[13] S. Lei et al., “Surface functionalization of two-dimensional metal chalcogenides by Lewis acid–base chemistry,” Nat. Nanotechnol., vol. 11, no. 5, pp. 465–471, Feb. 2016.[14] J. Li, J. Kang, Q. Cai, W. Hong, C. Jian, and W. Liu, “Boosting Hydrogen Evolution Performance of MoS2 by Band Structure Engineering,” Adv. Mater. Interfaces, vol. 1700303, 2017.[15] J. Jiang et al., “Intercalation doped multilayer-graphene-nanoribbons for next-generation interconnects,” Nano Lett., vol. 17, no. 3, pp. 1482–1488, Mar. 2017.[16] J. Jiang, J. Kang, and K. Banerjee, “Characterization of Self - Heating and Current - Carrying Capacity of Intercalation Doped Graphene - Nanoribbon Interconnects,” in IEEE International Reliability Physics Symposium, 2017, p. 6B.1.1-6B.1.6.[17] X. Li et al., “Graphene inductors for high-frequency applications - design, fabrication, characterization, and study of skin effect,” in IEEE International Electron Devices Meeting, 2014, p. 5.4.1-5.4.4.[18] J. Kang et al., under review.[19] J. Kang et al., under review

Lokalisierung und freie Positionierung unter Verwendung eines kooperativen Multi-Spulensendesystems für die drahtlose Energieübertragung

With the continuous development of communication technology there are more and more portable devices requiring periodic charging with a cable and power socket. Wireless power transfer (WPT) technology provides a promising solution to overcome the inconvenience, potential safety hazard and unsightliness of power supply cables. The result of this thesis is a conceptual design for an optimized 100 kHz WPT system having a large charging pad allowing free placement of the device to be charged. The system has high efficiency and is Electromagnetic Compatibility friendly. The three-coil system, composed of a single transmitter coil and two coils in the receiver, is operating in series resonance and has been optimized by synthesis of the coupling coefficient and quality factor to provide maximum efficiency and power simultaneously. Unique to the proposed design is that the single transmitter coil is replaced with 4-coil structure which enables field forming to strengthen the field in the center of the 4-coil structure and reduce it at the margins. A transmitter matrix consisting of cooperative multiple coils is proposed to increase the charging pad area and reduce the external magnetic field. A 16 coils system is selected as most cost efficiency. The transmitter coil radius is optimized using the criterion of weighted overall efficiency, which results in high efficiency with minimal emission to the surroundings. During charging, the appropriate 4-coil structure is activated, depending on the device location, with the other coils turned off. Several algorithms are presented that enable localization of the receiver position including: grid search, Gauss-Newton and reflected impedance for combined coils. COMSOL simulation is used to investigate the effects of using ferrite, aluminum loading and a reactive resonant coil to improve system efficiency and reduce external fields below specified human exposure limits. This thesis provides a WPT solution for charging mobile and portable devices that has many advantages. The proposed 100 kHz 16 coils transmitter matrix WPT system, consisting of individually activated 4-coil sub structures, allows free placement within the charging area, more than 65% transfer efficiency at 10 cm transmission distance and electromagnetic field emission considerably less than required by guidelines.Mit fortschreitender Entwicklung der Kommunikationstechnik steigt die Anzahl tragbarer Geräte, die einen wiederholten Ladevorgang über ein Kabel benötigen, kontinuierlich. Drahtlose Energieübertragung (Wireless Power Transfer, WPT) umgeht die damit verbundenen Sicherheitsrisiken sowie die Unbequemlichkeiten und Unansehnlichkeit, die eine große Zahl an Ladekabeln mit sich bringt. Im Rahmen dieser Arbeit ist ein konzeptueller Entwurf für ein optimiertes 100 kHz WPT-System entstanden, welcher einen großen Ladebereich mit der Möglichkeit zur freien Platzierung des zu ladenden Gerätes erlaubt. Das System zeichnet sich durch eine hohe Effizienz und elektromagnetische Verträglichkeit aus. Ein Dreispulensystem, bestehend aus einer Sendespule und zwei Empfängerspulen in Serienresonanz, wird hinsichtlich Kopplungsfaktor und Gütefaktor optimiert. Die Sendespule wird durch eine 4-Spulen Struktur ersetzt, die eine Feldformung ermöglicht, so dass eine Verstärkung des Feldes im Zentrum der Struktur erreicht wird bei gleichzeitiger Abschwächung an den Rändern. Sendermatrizen aus kooperativen Mehrspulensystemen werden untersucht mit dem Ziel, die Fläche des Ladefeldes zu vergrößern und das externe magnetische Feld zu reduzieren. Ein System aus 16 Spulen wird als das mit dem besten Kosten-Effizienz Verhältnis identifiziert. Der Radius der Senderspulen wird nach einem Kriterium der gewichteten Gesamteffizienz optimiert. Ziel ist eine hohe Effizienz bei gleichzeitig minimalen Emissionen in die Umgebung. Beim Ladevorgang wird in Abhängigkeit von der Position des zu ladenden Geräts die passende 4-Spulen Struktur aktiviert während die übrigen deaktiviert bleiben. Zur Lokalisierung des Empfängers werden die Algorithmen Rastersuche, Gauss-Newton und reflektierte Impedanz für kombinierte Spulen vorgestellt. Zur Untersuchung der Effekte von Ferriten und Aluminium sowie reaktiver resonanter Spulen wurden Simulationen mit COMSOL durchgeführt, mit dem Ziel die Effizienz zu erhöhen und die externen Felder zu reduzieren, so dass die Grenzwerte für die menschliche Exposition unterschritten werden. Diese Arbeit liefert eine WPT-Lösung für das Laden mobiler und portabler Geräte welche zahlreiche Vorteile bietet. Das vorgeschlagene 100 kHz 16-Spulen Matrixsystem, bestehend aus individuell aktivierbaren 4-Spulen Teilstrukturen, ermöglicht eine freie Platzierung auf dem Ladebereich, mehr als 65 % Übertragungseffizient im Abstand von 10 cm sowie deutlich geringere Elektromagnetische Feld Emissionen als in den Richtlinien gefordert

Development of a hybrid microwave-optical system to monitor human thermoregulation

Warming of human tissue causes vasodilation and therefore, increase in blood volume. Such thermal responses allow the assessment of hemodynamics in the tissue, providing physiological and clinically important information of the diagnosed subject. Local warming is often accomplished on the skin because of its accessibility and simplicity. To allow the investigation into deeper tissue such as the muscle, an innovative hybrid microwave-optical system has been developed. This comprises of a microwave system, an optical monitoring and cooling system. The tissue warming is induced by a novel microwave applicator, which was based on microstrip patch design operating at 2.45 GHz with a superstrate interface layer to improve the coupling of electromagnetic (EM) waves into the skin. The active cooling was introduced to reduce skin heating. While the optical sensors based on Near-Infrared Spectroscopy (NIRS), was used to measure the changes in tissue oxygenation including the muscle. This thesis demonstrates the development procedure, covering the design and operation of the entire system. Moreover, the majority of the work is based on the four developed applicators, where each design was evaluated using EM and thermal simulation based on numerical phantoms. The study evaluates the distribution of absorbed EM energy in the tissue known as the specific absorption rate (SAR). The applicators are developed in the following order: (i) Applicator I was fabricated for preliminary study for general tissue heating with the integrated optical probes. This early study provided an insight to the importance of superstrate thickness and material. (ii) Applicator II, which introduces a new approach to skin cooling based on Thermoelectric Coolers (TEC) and high thermal conductive superstrate. This design could cool the skin and monitor tissue oxygenation, skin perfusion and temperature. (iii) Applicator III was an updated model of the predecessor, resolving cooling configuration and the discrepancy in operating frequency, and was capable of minimising skin heating effectively (iv) Circularly polarized (CP) Applicator aimed at reduction of the SAR in the superficial layer, and hence skin heating. The simulated thermal study of all developed applicators was validated with exvivo (mimicked phantom) and in-vivo experimental trials. The measurements and the simulation model were in agreement, apart from the CP applicator due to the complexity of measurement. The results from the phantom and human calf indicated superficial heating was reduced by about 5.0-6.0 ° C when skin cooling was applied, while the temperature change in muscle was not significantly affected. The measurement with mimicked tissue showed the applicator was capable of elevating muscle temperature by approximately 3.0-4.0 ° C. This is a sufficient increase to cause tissue dilation, and therefore, change in the thermal response. The hybrid microwave-optical system has been developed and examined on three human calves during in-vivo physiological study. The results using Applicator II illustrated that the device can successfully stimulate and measure thermal responses in terms of oxy/deoxy/total haemoglobin concentrations changes ( HbO2/ HHb/ HbT). The slope (rate of change) of HbT curve during microwave exposure is defined as the thermal response. This parameter is essential in studying physiological responses between different subject, particularly in vascular diseases, transplanted free flaps and other conditions, including chronic spinal cord injury. Subjects with such conditions will have a distinguishable response to tissue heating than a healthy subject. The monitored haemodynamic signals of Applicator II are primarily based on superficial responses. However, measurements with Applicator III showed the potential of the applicator. The measured thermal response was 0.83 10 3×10⁻³ μM/s without skin cooling, which was dedicated by skin heating. The introduced cooling system has reduced the skin temperature and maintained the local skin micro-circulation, which was monitored with the secondary optical system based on Laser Doppler Flowmetry (LDF). This probe measures blood flow at superficial depth, and consequently, was used as a validation tool to demonstrate the cooling efficiency. The measured thermal response with skin over-cooling was -0.08 10 3×10⁻³ μM/s. The negative response indicates arterial constriction, and therefore, the skin heat was eliminated while the simulations study to indicate the muscle temperature was elevated by 3 ° C. However, the response was dominant by the superficial response. Obtaining a response from muscle only was challenging and currently being solved in numerous applicator and cooling technique, which have been presented in the thesis