Design of High Efficiency Broadband Adjusted Class AB Power Amplifier

This thesis starts with a discussion of different classes of operation of power amplifiers (PAs). Comparing advantages and disadvantages of these classes, class AB is chosen as the best initial candidate for the design of broadband PA. Different methods for design of matching networks are first discussed. Some of them fall into the group of narrowband matching networks, while others are suitable for a broadband context. Broadband design methodologies are categorized into two groups of real-to-real transformations and complex-to-real transformations. Complex-to-real transformations are the most useful methods for this project, since design of power amplifiers deals with complex loads rather than just real loads. The design of broadband matching networks exploiting filter theory is presented in this thesis for synthesizing broadband and highly efficient power amplifiers (PAs). Starting with sets of optimum impedances over the targeted frequency band, the matching networks are designed using a systematic approach. The effects of load termination at the 2nd and 3rd harmonic on the PA performance (efficiency) are studied. The significance of proper termination, especially at the 2nd harmonic, is highlighted. To prevent further complication of the design process, though, specific harmonic termination (stubs) is avoided and special arrangement of the matching network (position of the bias network) is preferred, as it is found to lead to acceptable efficiency. Two PA prototypes were designed with the proposed methodology using 25W GaN devices. The designs targeted two frequency bands: 1.8 to 2.2 GHz (20% BW) and 1.8 to 2.7 GHz (40% BW). For the former, drain efficiency (DE) of 70% (+/–5%) and output power of 45.5 dBm (+/- 1.0dB) was measured while the latter achieved very promising efficiency of about 60% over the entire bandwidth

Flexible operation of grid-interfacing converters in distribution networks : bottom-up solutions to voltage quality enhancement

Due to the emerging application of distributed generation (DG), large numbers of DG systems are expected to deliver electricity into the distribution network in the near future. For the most part these systems are not ready for riding through grid disturbances and cannot mitigate unwanted influences on the grid. On the one hand, with the increasing use of sensitive and critical equipment by customers, the electricity network is required to serve high voltage quality. On the other hand, more and more unbalanced and nonlinear equipment, including DG units, is negatively affecting the power quality of distribution networks. To adapt to the future distribution network, the tendency for grid-interfacing converters will be to integrate voltage quality enhancement with DG functionality. In this thesis, the flexible operation of grid-interfacing converters in distribution networks is investigated for the purpose of voltage quality enhancement at both the grid and user sides. The research is carried out in a bottom-up fashion, from the low-level power electronics control, through the realization of individual system functionality, finally arriving at system-level concepts and implementation. Being essential to the control of grid-interfacing converters, both stationaryframe techniques for voltage detection and synchronization in disturbed grids, and asymmetrical current regulation are investigated. Firstly, a group of high performance filters for the detection of fundamental symmetrical sequences and harmonics under various grid conditions is proposed. The robustness of the proposed filters to small grid-frequency variation and their adaptability to large frequency change are discussed. Secondly, multiple reference frame current regulation is explored for dealing with unbalanced grid conditions. As a complement to the existing proportional resonant (PR) controllers, sequence-decoupled resonant (SDR) controllers are proposed for regulating individual symmetric sequences. Based on the modeling of a four-leg grid-connected system in different reference frames, three types of controllers, i.e. PI, PR, and proportional plus SDR controllers are compared. Grid-interactive control of distributed power generation, i.e. voltage unbalance compensation, grid-fault ride-through control and flexible power transfer, as well as the modeling of harmonic interaction, are all investigated. The in-depth study and analysis of these grid interactions show the grid-support possibilities and potential negative impact on the grid of inverter-based DG units, beyond their primary goal of power delivery. In order to achieve a co-operative voltage unbalance compensation based on distributed DG systems, two control schemes, namely voltage unbalance factor based control and negative-sequence admittance control, are proposed. The negativesequence voltages at the grid connection point can be compensated and mitigated by regulating the negative-sequence currents flowing between the grid and DG converters. Flexible active and reactive power control during unbalanced voltage dips is proposed that enables DG systems to enhance grid-fault ride-through capability and to adapt to various requirements for grid voltage support. By changing adaptable weighting factors, the compensation of oscillating power and the regulation of grid currents can be easily implemented. Two joint strategies for the simultaneous control of active and reactive power are derived, which maintain the adaptive controllability that can cope with multiple constraints in practical applications. The contribution of zero-sequence currents to active power control is also analyzed as a complement to the proposed control, which is based on positive- and negative-sequence components. Harmonic interaction between DG inverters and the grid is modeled and analyzed with an impedance-based approach. In order to mitigate the harmonic distortion in a polluted grid, it is proposed to specify output impedance limits as a design constraint for DG inverters. Results obtained from modeling, analysis, and simulations of a distribution network with aggregated DG inverters, show that the proposed method is a simple and effective way for estimating harmonic quasi-resonance problems. By integrating these proposed control strategies in a modified conventional series-parallel structure, we arrived at a group of grid-interfacing system topologies that is suitable for DG applications, voltage quality improvement, and flexible power transfer. A concrete laboratory system details the proposed concepts and specifies the practical problems related to control design. The introduction of multi-level control objectives illustrates that the proposed system can ride through voltage disturbances, can enhance the grid locally, and can continue the power transfer to and from the grid while high voltage quality is maintained for the local loads within the system module. A dual-converter laboratory set-up was built, with which the proposed concepts and practical implementation have been fully demonstrated

Design methods for microwave filters and multiplexers

This thesis is concerned with developing synthesis and design procedures for microwave filters and multiplexers. The core of this thesis presents the following topics. 1) New classes of lumped lowpass prototype filters satisfying generalized Chebyshev characteristics have been investigated. Exact synthesis procedures are given using a relatively new technique termed the alternating pole synthesis technique to solve the accuracy problem. The properties of these filters and their practical advantages have been discussed. Tables of element values for commonly used specifications are included. 2) A new design procedure has been developed for bandpass channel multiplexers connected at a common junction. This procedure is for multiplexers having any number of Chebyshev channel filters, with arbitrary degrees, bandwidths and inter-channel spacings. The procedure has been modified to allow the design of multi-octave bandwidth combline channel filter multiplexers. It is shown that this procedure gives very good results for a wide variety of specifications, as demonstrated by the computer analysis of several multiplexers examples and by the experimental results. 3) A compact exact synthesis method is presented for a lumped bandpass prototype filter up to degree 30 and satisfies a generalized Chebyshev response. This prototype has been particularly utilized in designing microwave broadband combline filters. 4) Different forms of realization have been discussed and used in design and construction of different devices. This includes a new technique to realize TEM networks in coaxial structure form having equal diameter coupled circular cylindrical rods between parallel ground planes. Other forms of realization have been discussed ranging from equal diameter posts, direct coupled cavity waveguide filters to microwave integrated circuits using suspended substrate stripline structure. The experimental results are also given. In addition, the fundamentals of lumped circuits and distributed circuits have been briefly reviewed. The approximation problem was also discussed

Characterization and modeling of a coaxial cavity quadruplet based filter for mobile phone LTE-2 band

En aquest projecte es tracta la caracterització i modelatge d'un filtre de cavitats mitjançant el simulador electromagnètic 3D HFSS. Partint de les especificacions d'un filtre real de telefonia es realitzarà una caracterització completa, modelat i extracció del diagrama nodal ideal. Per a aconseguir-ho, prèviament s'estudiarà el tipus de responsa a aconseguir i es caracteritzarà amb polinomis. Amb l'enfocament de la matriu d'acoblament, primer un conjunt de característiques dels paràmetres S són creats. Seguidament es defineix una topologia del filtre adecuada i finalment la corresponent matriu d'acoblament és sintetitzada. Aquesta matriu d'acoblament defineix tot el filtre, i amb això el corresponent filtre físic pot ser dissenyat i fabricat. Per tancar l'intèrval entre la representació de la matriu d'acoblament d'un filtre i el filtre físic, es dónen uns mètodes per mesurar/calcular els acoblaments i el Q extern. Aquests paràmetres poden ser determinats amb l'ús d'un simulador EM 3D com l'utilitzat en aquest projecte, HFSS.En este proyecto se trata la caracterización y modelado de un filtro de cavidad mediante el simulador electromagnético 3D HFSS. Partiendo de las especificaciones de un filtro real de telefonía se realizará una caracterización completa, modelado y extracción de diagrama nodal ideal. Para ello previamente se estudiará el tipo de respuesta a conseguir y se caracterizará con polinomios. Con el enfoque de la matriz de acoplo, primero un conjunto de características de los parámetros S son creadas. Seguidamente se define una topología del filtro adecuada y finalmente la correspondiente matriz de acoplo es sintetizada. Esta matriz de acoplo define del todo al filtro, y con esto el correspondiente filtro físico puede ser diseñado y fabricado. Para cerrar el intervalo entre la representación de la matriz de acoplo de un filtro y el filtro físico, se dan unos métodos para medir/calcular los acoplos y el Q externo. Estos parámetros pueden ser determinados con el uso de un simulador EM 3D como el utilizado en este proyecto, HFSS.In this project the characterization of a cavity filter by 3D electromagnetic simulator HFSS is proposed. Based on the specifications of a real cellular filter complete characterization, modeling and ideal nodal diagram extraction will be performed. To do so, previously the kind of response to achieve will be studied and characterized with polynomials. With the coupling matrix synthesis approach, a set of filter S-parameter characteristics is first created. Then a suitable filter topology is defined and finally the corresponding coupling matrix is synthesized. This coupling matrix fully defines the filter and, with this at hand, the corresponding physical filter can be designed and manufactured. To close the gap between the coupling matrix representation of a filter and the physical filter, practical directions about how to measure/calculate coupling bandwidths and external Q are given. These parameters can be determined by use of 3D EM simulator as the one used in this project, HFSS

Filter Design in Coaxial Cavities

A classical topic in Telecommunication Engineering is filter design at microwave frequencies. It constitutes a complex problem and therefore the whole process is divided into several stages, whose analysis is the general aim of this study. Firstly the approximation problem is addressed by means of the generalised Chebychev method. After a process of finite transmission zeros allocation is carried out, the design polynomials are obtained. They meet the specifications typically given in the frequency domain. From the design polynomials of the preceding stage the synthesis of the coupling matrix is developed. The coupling matrix stores information which can be directly translated into useful equivalent circuits upon which filter design at microwave frequencies is based. Sometimes there are values (i.e. called couplings) that must be annihilated in order to obtain a practical circuit topology. Towards that end matrix rotations are introduced. Regarding physical filter design, this study raises three different approaches. In the context of lowpass filters, a stepped impedance filter is designed in coaxial technology. Both circuital and full-wave optimization are introduced under this scenario. With respect to bandpass filters, several waveguide direct-coupled filters are designed. Their full-wave responses are optimized for the sake of improvement. Finally, in the same scenario of bandpass filter design a further step is taken, and a method based on sequential stages is proposed. It is applied over a combline filter in the S-Band for mobile communications. Budget and time constraints have prevented us from doing the manufacturing process, which could be addresses in the near future.Un escenario típico en Ingeniería de Telecomunicación es el diseño de filtros de radiofrecuencia. Es un problema complejo, por lo que habitualmente se aborda en varias etapas. El análisis de las mismas es el propósito general de este trabajo. En primer lugar se decide resolver el problema de la aproximación por medio del método generalizado de Chebychev. Tras el establecimiento de los pertinentes ceros de transmisión finitos, este método obtiene los polinomios de diseño. La respuesta asociada a dichos polinomios cumple las especificaciones de diseño, típicamente dadas a través de una máscara en el dominio de la frecuencia. En la siguiente etapa de diseño se enmarca la síntesis de la matriz de acoplos. La información numérica que almacena esta matriz se traduce directamente en un equivalente circuital. El diseño de filtros de radiofrecuencia sienta sus bases en la aproximación de estructuras de radiofrecuencia a modelos equivalentes, por lo que la matriz de acoplos se convierte en una herramienta de gran utilidad. Se introduce adicionalmente el concepto de rotación como proceso adicional de eliminación de acoplos. Dicho proceso puede ser requerido para obtener una implementación sencilla en las estructuras típicas de radiofrecuencia. Con respecto a la realización física de filtros, se plantean tres aproximaciones. En el contexto de los filtros paso bajo se diseña un filtro de secciones cortas en coaxial. En este escenario se introducen tanto la optimización circuital como la electromagnética. Con respecto a los filtros paso banda, se diseñan varios filtros de cavidades de acoplos directos. Una vez finalizado su diseño se lleva a cabo un proceso adicional de optimización para mejorar sus prestaciones. Finalmente, en este mismo escenario de aproximaciones paso banda se propone un método basado en subdivisión de etapas. Dicho método se aplica en el diseño de un filtro combline en banda S para comunicaciones móviles. Por limitaciones de tiempo y presupuesto no se ha llevado a cabo la fabricación de ningún prototipo, quedando esta tarea como objetivo a desarrollar en un futuro cercano

Coreless planar transformer for hard-switching applications

Leistungshalbleiter werden meist in schaltenden Anwendungen eingesetzt. Hartes Schalten ist hierfür ein gängiges und einfaches Funktionsprinzip, insbesondere bei induktiven Lasten. Hier können durch Verkürzung der Übergangsdauer zwischen Spannung und Strom die Schaltverluste reduziert werden. Die Nachteile schnellerer Übergänge in hart schaltenden Anwendungen sind in der Regel höhere Überschwingungen und außerdem die Erzeugung von elektromagnetischen Störungen. Die maximale Überspannung wird hierbei durch die Sperrspannung des Halbleiters begrenzt. Ein gängiger Ansatz zur Reduzierung der Überspannungen für einen Leistungshalbleiter ist die Minimierung der Induktivität im Leistungspfad. Ein in Reihe mit den Leistungsanschlüssen des Halbleiters geschalteter Transformator kann jedoch für verschiedene Anwendungen von Vorteil sein. Insbesondere die hohen Stromgradienten bei schnellen, harten Schaltvorgängen sorgt für eine hohe, und somit gut nutzbare Ausgangsspannung des Transformators. In dieser Arbeit wird ein neues Design eines kernlosen Planartransformators vorgestellt. Eine hohe magnetische Kopplung und ein einstellbares Übersetzungsverhältnis sowie eine besonders hohe Bandbreite sorgen dafür, dass die Induktivität in Reihe mit dem Halbleiter minimal gehalten werden kann. Der zweischichtige Aufbau ist zudem für verschiedene Substrate, insbesondere Leiterplatten, geeignet. Ein bis zur ersten Resonanzfrequenz gültiges Simulationsmodell des neuen Übertragerdesigns wurde erstellt und verifiziert. Die Anwendung, für die der Übertrager in dieser Arbeit hauptsächlich eingesetzt wird, ist das induktive Feed-Forward-Verfahren. Diese Methode zur Steuerung von Leistungshalbleitern beschleunigt das Umschalten in hart schaltenden Anwendungen. Die Methode wird analysiert und Verbesserungen für eine Auswahl von Leistungshalbleiter-Designs werden vorgeschlagen und verifiziert. Weiterhin wird die Ansteuerungsmethode modifiziert, um symmetrische Stromgradienten in parallel geschalteten Leistungshalbleitern zu erreichen. Außerdem wird der Übertrager vergleichbar zu einer Rogowski-Spule als Stromsensor genutzt, um die hohen Stromgradienten beim Schalten zu charakterisieren. Es wird gezeigt, dass durch verpolung der Sekundärwicklung das induktive Feed-Forward-Verfahren zur Verlangsamung des Schaltvorganges eingesetzt werden kann. In der letzten in dieser Arbeit vorgestellten Anwendung wird der Übertrager zur Erzeugung einer isolierten Versorgungsspannung für die Gate Ansteuerung eingesetzt. Die Anwendung ist besonders vorteilhaft, wenn eine negative Versorgungsspannung erforderlich ist, z.B. aufgrund einer niedrigen Schwellspannung

Design and Power Management of an Offshore Medium Voltage DC Microgrid Realized Through High Voltage Power Electronics Technologies and Control

The growth in the electric power industry’s portfolio of Direct Current (DC) based generation and loads have captured the attention of many leading research institutions. Opportunities for using DC based systems have been explored in electric ship design and have been a proven, reliable solution for transmitting bulk power onshore and offshore. To integrate many of the renewable resources into our existing AC grid, a number of power conversions through power electronics are required to condition the equipment for direct connection. Within the power conversion stages, there is always a requirement to convert to or from DC. The AC microgrid is a conceptual solution proposed for integrating various types of renewable generation resources. The fundamental microgrid requirements include the capability of operating in islanding mode and/or grid connected modes. The technical challenges associated with microgrids include (1) operation modes and transitions that comply with IEEE1547 without extensive custom engineering and (2) control architecture and communication. The Medium Voltage DC (MVDC) architecture, explored by the University of Pittsburgh, can be visualized as a special type of DC microgrid. This dissertation is multi-faceted, focused on many design aspects of an offshore DC microgrid. The focal points of the discussion are focused on optimized high power, high frequency magnetic material performance in electric machines, transformers, and DC/DC power converters – all components found within offshore power system architectures. A new controller design based upon model reference control is proposed and shown to stabilize the electric motor drives (modeled as constant power loads), which serve as the largest power consuming entities in the microgrid. The design and simulation of a state-of-the-art multilevel converter for High Voltage DC (HVDC) is discussed and a component sensitivity analysis on fault current peaks is explored. A power management routine is proposed and evaluated as the DC microgrid is disturbed through various mode transitions. Finally, two communication protocols are described for the microgrid – one to minimize communication overhead inside the microgrid, and another to provide robust and scalable intra-grid communication. The work presented is supported by Asea Brown Boveri (ABB) Corporate Research Center within the Active Grid Infrastructure program, the Advanced Research Project Agency – Energy (ARPA-E) through the Solar ADEPT program, and Mitsubishi Electric Corporation (MELCO)

Diplexers and multiplexers design by using coupling matrix optimisation

Microwave filters and multiplexers are used in many application areas and have been studied for decades. However, with increasing demands on communications and radar systems more complex filters are required which not only have superior performance but also are required to be small and lightweight. This thesis looks at new techniques in microwave filter design to achieve these aims. Coupled resonator circuits are of importance for design of RF/microwave narrow-band filters with any type of resonator regardless its physical structure. The coupling matrix is used to represent the coupled resonator circuit. Each matrix entry value refers to a physical dimension of the circuit. The response of the circuit can also be calculated by using the coupling matrix. Different methods are developed to generate the coupling matrix. This thesis presents designs of the coupled resonator based diplexers and multiplexers by using the coupling matrix local optimisation technique. The design procedures and measurement performance of 3 X-band (8.2-12.4 GHz) rectangular waveguide circuits, including a 10th order diplexer, a 4th order diplexer with cross-couplings and a 4-channel multiplexer, are presented. A novel computer-aided physical structure tuning technique, called Step Tune method, is also presented in this thesis