Projeto de controladores robustos para acionamento de um motor de indução trifásico

Pós-graduação em Engenharia Elétrica - FEIS

Microinversor integrado ao módulo fotovoltaico para sistemas conectados à rede elétrica utilizando controlador ressonante

This paper shows the modeling and control of a single-phase full-bridge inverter with high-frequency transformer that may be used as part of a two-stage converter with transformerless DC-DC side or as a single-stage converter (simple DC-AC converter) for grid-connected PV applications. The inverter is modeled in order to obtain a small-signal transfer function used to design the P+Resonant current controller. A highfrequency step-up transformer results in reduced voltage switches and better efficiency compared with converters in which the transformer is used on the DC-DC side. Simulations and experimental results with a 200 W prototype are shown. 1

Modulation Techniques for Multi-Phase Converters and Control Strategies for Multi-Phase Electric Drives

The ever-increasing spread of automation in industry puts the electrical engineer in a central role as a promoter of technological development in a sector such as the use of electricity, which is the basis of all the machinery and productive processes. Moreover the spread of drives for motor control and static converters with structures ever more complex, places the electrical engineer to face new challenges whose solution has as critical elements in the implementation of digital control techniques with the requirements of inexpensiveness and efficiency of the final product. The successfully application of solutions using non-conventional static converters awake an increasing interest in science and industry due to the promising opportunities. However, in the same time, new problems emerge whose solution is still under study and debate in the scientific community During the Ph.D. course several themes have been developed that, while obtaining the recent and growing interest of scientific community, have much space for the development of research activity and for industrial applications. The first area of research is related to the control of three phase induction motors with high dynamic performance and the sensorless control in the high speed range. The management of the operation of induction machine without position or speed sensors awakes interest in the industrial world due to the increased reliability and robustness of this solution combined with a lower cost of production and purchase of this technology compared to the others available in the market. During this dissertation control techniques will be proposed which are able to exploit the total dc link voltage and at the same time capable to exploit the maximum torque capability in whole speed range with good dynamic performance. The proposed solution preserves the simplicity of tuning of the regulators. Furthermore, in order to validate the effectiveness of presented solution, it is assessed in terms of performance and complexity and compared to two other algorithm presented in literature. The feasibility of the proposed algorithm is also tested on induction motor drive fed by a matrix converter. Another important research area is connected to the development of technology for vehicular applications. In this field the dynamic performances and the low power consumption is one of most important goals for an effective algorithm. Towards this direction, a control scheme for induction motor that integrates within a coherent solution some of the features that are commonly required to an electric vehicle drive is presented. The main features of the proposed control scheme are the capability to exploit the maximum torque in the whole speed range, a weak dependence on the motor parameters, a good robustness against the variations of the dc-link voltage and, whenever possible, the maximum efficiency. The second part of this dissertation is dedicated to the multi-phase systems. This technology, in fact, is characterized by a number of issues worthy of investigation that make it competitive with other technologies already on the market. Multiphase systems, allow to redistribute power at a higher number of phases, thus making possible the construction of electronic converters which otherwise would be very difficult to achieve due to the limits of present power electronics. Multiphase drives have an intrinsic reliability given by the possibility that a fault of a phase, caused by the possible failure of a component of the converter, can be solved without inefficiency of the machine or application of a pulsating torque. The control of the magnetic field spatial harmonics in the air-gap with order higher than one allows to reduce torque noise and to obtain high torque density motor and multi-motor applications. In one of the next chapters a control scheme able to increase the motor torque by adding a third harmonic component to the air-gap magnetic field will be presented. Above the base speed the control system reduces the motor flux in such a way to ensure the maximum torque capability. The presented analysis considers the drive constrains and shows how these limits modify the motor performance. The multi-motor applications are described by a well-defined number of multiphase machines, having series connected stator windings, with an opportune permutation of the phases these machines can be independently controlled with a single multi-phase inverter. In this dissertation this solution will be presented and an electric drive consisting of two five-phase PM tubular actuators fed by a single five-phase inverter will be presented. Finally the modulation strategies for a multi-phase inverter will be illustrated. The problem of the space vector modulation of multiphase inverters with an odd number of phases is solved in different way. An algorithmic approach and a look-up table solution will be proposed. The inverter output voltage capability will be investigated, showing that the proposed modulation strategy is able to fully exploit the dc input voltage either in sinusoidal or non-sinusoidal operating conditions. All this aspects are considered in the next chapters. In particular, Chapter 1 summarizes the mathematical model of induction motor. The Chapter 2 is a brief state of art on three-phase inverter. Chapter 3 proposes a stator flux vector control for a three- phase induction machine and compares this solution with two other algorithms presented in literature. Furthermore, in the same chapter, a complete electric drive based on matrix converter is presented. In Chapter 4 a control strategy suitable for electric vehicles is illustrated. Chapter 5 describes the mathematical model of multi-phase induction machines whereas chapter 6 analyzes the multi-phase inverter and its modulation strategies. Chapter 7 discusses the minimization of the power losses in IGBT multi-phase inverters with carrier-based pulse width modulation. In Chapter 8 an extended stator flux vector control for a seven-phase induction motor is presented. Chapter 9 concerns the high torque density applications and in Chapter 10 different fault tolerant control strategies are analyzed. Finally, the last chapter presents a positioning multi-motor drive consisting of two PM tubular five-phase actuators fed by a single five-phase inverter.

Power Converters and Electric Drives for Smart Grid Applications

The present dissertation aims to explore, theoretically and experimentally, the problems and the potential advantages of different types of power converters for “Smart Grid” applications, with particular emphasis on multi-level architectures, which are attracting a rising interest even for industrial requests. The models of the main multilevel architectures (Diode-Clamped and Cascaded) are shown. The best suited modulation strategies to function as a network interface are identified. In particular, the close correlation between PWM (Pulse Width Modulation) approach and SVM (Space Vector Modulation) approach is highlighted. An innovative multilevel topology called MMC (Modular Multilevel Converter) is investigated, and the single-phase, three-phase and "back to back" configurations are analyzed. Specific control techniques that can manage, in an appropriate way, the charge level of the numerous capacitors and handle the power flow in a flexible way are defined and experimentally validated. Another converter that is attracting interest in “Power Conditioning Systems” field is the “Matrix Converter”. Even in this architecture, the output voltage is multilevel. It offers an high quality input current, a bidirectional power flow and has the possibility to control the input power factor (i.e. possibility to participate to active and reactive power regulations). The implemented control system, that allows fast data acquisition for diagnostic purposes, is described and experimentally verified.

Circuiti per il miglioramento della qualità di sorgenti dc

Tutti gli apparati elettronici richiedono un'alimentazione in tensione continua. Qualunque sia la fonte di energia elettrica, una batteria (in DC) o la rete di distribuzione (in AC), l’alimentatore ha il compito di regolare la tensione continua di uscita per consentire il corretto funzionamento del dispositivo alimentato. La stabilizzazione della tensione DC in uscita deve avvenire nonostante la presenza di ripple e di disturbi sulla alimentazione primaria, di ampie variazioni sulle correnti assorbite dal carico, di ampie escursioni di temperatura e deve essere garantita nel tempo, anche a fronte di sostituzione di alcuni componenti del circuito. In questa tesi si prenderanno in considerazione i regolatori lineari. Sebbene si tratti di circuiti che operano in condizioni di linearità e quindi, quasi per definizione, poco efficienti, in realtà il loro impiego diventa quasi obbligatorio per applicazioni in cui è richiesta una tensione di alimentazione poco rumorosa. Se utilizzati a valle di un alimentatore switching possono aumentare notevolmente la qualità della tensione di uscita operando con livelli di efficienza e di dissipazione del tutto accettabili e con minimo aumento di costo del sistema. Gli alimentatori lineari non sono dunque “superati” dai più recenti alimentatori switching ma sono, piuttosto, “alternativi” e, in molti alimentatori moderni, di complemento. Per questo motivo, anche di recente, sono stati sviluppati e trovano importanti quote di mercato innovative architetture di regolatori lineari dalle prestazioni molto migliorate e vi sono circuiti come il regolatore di John Linsley Hood che non possono non suscitare il più vivo interesse della comunità audiofila

Adaptive control of sinusoidal brushless DC motor actuators

Electrical Power Assisted Steering system (EPAS) will likely be used on future automotive power steering systems. The sinusoidal brushless DC (BLDC) motor has been identified as one of the most suitable actuators for the EPAS application. Motor characteristic variations, which can be indicated by variations of the motor parameters such as the coil resistance and the torque constant, directly impart inaccuracies in the control scheme based on the nominal values of parameters and thus the whole system performance suffers. The motor controller must address the time-varying motor characteristics problem and maintain the performance in its long service life. In this dissertation, four adaptive control algorithms for brushless DC (BLDC) motors are explored. The first algorithm engages a simplified inverse dq-coordinate dynamics controller and solves for the parameter errors with the q-axis current (iq) feedback from several past sampling steps. The controller parameter values are updated by slow integration of the parameter errors. Improvement such as dynamic approximation, speed approximation and Gram-Schmidt orthonormalization are discussed for better estimation performance. The second algorithm is proposed to use both the d-axis current (id) and the q-axis current (iq) feedback for parameter estimation since id always accompanies iq. Stochastic conditions for unbiased estimation are shown through Monte Carlo simulations. Study of the first two adaptive algorithms indicates that the parameter estimation performance can be achieved by using more history data. The Extended Kalman Filter (EKF), a representative recursive estimation algorithm, is then investigated for the BLDC motor application. Simulation results validated the superior estimation performance with the EKF. However, the computation complexity and stability may be barriers for practical implementation of the EKF. The fourth algorithm is a model reference adaptive control (MRAC) that utilizes the desired motor characteristics as a reference model. Its stability is guaranteed by Lyapunov’s direct method. Simulation shows superior performance in terms of the convergence speed and current tracking. These algorithms are compared in closed loop simulation with an EPAS model and a motor speed control application. The MRAC is identified as the most promising candidate controller because of its combination of superior performance and low computational complexity. A BLDC motor controller developed with the dq-coordinate model cannot be implemented without several supplemental functions such as the coordinate transformation and a DC-to-AC current encoding scheme. A quasi-physical BLDC motor model is developed to study the practical implementation issues of the dq-coordinate control strategy, such as the initialization and rotor angle transducer resolution. This model can also be beneficial during first stage development in automotive BLDC motor applications.

Stability and Transient Performance Assessment in a COTS-Module-Based Distributed DC/DC System

This paper introduces a method to analyze and predict stability and transient performance of a distributed system where COTS (Commercial-off-the-shelf) modules share an input filter. The presented procedure is based on the measured data from the input and output terminals of the power modules. The required information for the analysis is obtained by performing frequency response measurements for each converter. This attained data is utilized to compute special transfer functions, which partly determine the source and load interactions within the converters. The system level dynamic description is constructed based on the measured and computed transfer functions introducing cross-coupling mechanisms within the system. System stability can be studied based on the well-known impedance- related minor-loop gain at an arbitrary interface within the system.

Excitación y control de IGBTs de un inversor trifásico sinusoidal

El origen del proyecto se encuentra en la mejora de un inversor trifásico sinusoidal comercial sobre la base del estudio de las técnicas de excitación óptimas para los IGBTs que lo componen en su etapa de potencia. En las primeras fases de planteamiento del proyecto se propone una idea mucho más ambiciosa, la realización de un nuevo convertidor de emergencia, destinado al sector ferroviario, para dar servicio de climatización. Este convertidor está formado por la asociación en cascada de un bloque DC/DC elevador y un bloque inversor DC/AC trifásico controlado mediante PWM con modulación sinusoidal. Se pretendía así dar solución a las siguientes problemáticas detectadas en los convertidores comercializados hasta el momento: un bloque elevador excesivamente sobredimensionado, subsistemas de control independientes para los dos bloques que configuran el convertidor, adicionalmente, la tarjeta driver se rediseña con cada cambio de especificaciones por parte de un nuevo cliente y finalmente, las comunicaciones tanto de diagnosis como de mantenimiento necesitaban una importante actualización. Inicialmente, se ha realizado un estudio teórico de los bloques elevador e inversor para poder realizar el diseño y dimensionamiento de sus componentes tanto semiconductores como electromagnéticos. Una vez completada la parte de potencia, se estudia el control que se realiza mediante medidas directas y simulación tanto de la estrategia de control del elevador como del inversor. Así se obtiene una información completa de la funcionalidad de las tarjetas existentes. Se desea realizar el diseño de una única tarjeta controladora y una única tarjeta de drivers para ambos bloques. Por problemas ajenos, en el transcurso de este proyecto se cancela su realización comercial, con lo que se decide al menos crear la placa de control y poder gobernar un convertidor ya existente, sustituyendo la tarjeta de control del bloque elevador. Para poder fabricar la placa de control se divide en dos tarjetas que irán conectadas en modo sándwich. En una tarjeta está el microcontrolador y en otra está todo el interface necesario para operar con el sistema: entradas y salidas digitales, entradas y salidas analógicas, comunicación CAN, y un pequeño DC/DC comercial que proporciona alimentación al prototipo. Se realiza un pequeño programa funcional para poder manejar el convertidor, el cual con una tensión de 110V DC, proporciona a la salida una tensión de 380V AC. Como ya se ha expuesto, debido a la cancelación del proyecto industrial no se profundiza más en su mejora y se decide proponerlo para su evaluación en su fase actual. ABSTRACT. The beginning of the project is found in the improvement of a commercial sine wave three phase inverter which is based in a study about optimal excitation techniques to IGBTs which compose in the power stage. In the early phases of project it is proposed a much more ambitious idea, the fact of a new emergency converter, proposed for the rail sector to work in an air condition unit. This converter is formed by an association of a block cascaded DC/DC booster and a block DC/AC inverter three-phase controlled by a sine wave modulation PWM. The purposed was to give a solution to following problems detected in commercial converters nowadays: an excessively oversized block boost, independent control subsystems for two blocks that configure the converter. In addition, driver board is redesigned with each specifications change demand it a new customer, and finally, the communications, diagnostic and maintenance that needed a important upgrade. Initially, it has been performed a theoretical study of boost and the inverter blocks to be able to perform the component’s design and the size (semiconductor and electromagnetic fields). Once finished power study, it is analysed the control performed using direct measures and simulation of boost control strategy and inverter. With this it is obtained complete information about existing cards functionality. The project is looking for the design of just one controller card and one drivers´ card for both blocks. By unrelated problems, during the course of this project a commercial realization. So at least its decided to create control board to be able to existing converter, replacing boost block’s control board. To be able to manufacture control board it is divided in two cards connected in sandwiching mode. In a card is microcontroller and in another is all needed interface to operate with the system: digital inputs and outputs, analogical inputs and outputs, CAN communication, and a small DC / DC business that provide power supply to the prototype. It is performed a small functional program to handle the converter, which with an input voltage 110V DC provides an output voltage 380V AC. As already has been exposed, due to industrial project cancellation it is decided no to continue with all improvements and directly to evaluate it in the current phase.

Methodology for Dynamic Stability and Robustness Analysis of Commercial-Power-Module-Based DC-Distributed Systems

El propósito de esta tesis es presentar una metodología para realizar análisis de la dinámica en pequeña señal y el comportamiento de sistemas de alimentación distribuidos de corriente continua (CC), formados por módulos comerciales. Para ello se hace uso de un método sencillo que indica los márgenes de estabilidad menos conservadores posibles mediante un solo número. Este índice es calculado en cada una de las interfaces que componen el sistema y puede usarse para obtener un índice global que indica la estabilidad del sistema global. De esta manera se posibilita la comparación de sistemas de alimentación distribuidos en términos de robustez. La interconexión de convertidores CC-CC entre ellos y con los filtros EMI necesarios puede originar interacciones no deseadas que dan lugar a la degradación del comportamiento de los convertidores, haciendo el sistema más propenso a inestabilidades. Esta diferencia en el comportamiento se debe a interacciones entre las impedancias de los diversos elementos del sistema. En la mayoría de los casos, los sistemas de alimentación distribuida están formados por módulos comerciales cuya estructura interna es desconocida. Por ello los análisis presentados en esta tesis se basan en medidas de la respuesta en frecuencia del convertidor que pueden realizarse desde los terminales de entrada y salida del mismo. Utilizando las medidas de las impedancias de entrada y salida de los elementos del sistema, se puede construir una función de sensibilidad que proporciona los márgenes de estabilidad de las diferentes interfaces. En esta tesis se utiliza el concepto del valor máximo de la función de sensibilidad (MPC por sus siglas en inglés) para indicar los márgenes de estabilidad como un único número. Una vez que la estabilidad de todas las interfaces del sistema se han evaluado individualmente, los índices obtenidos pueden combinarse para obtener un único número con el que comparar la estabilidad de diferentes sistemas. Igualmente se han analizado las posibles interacciones en la entrada y la salida de los convertidores CC-CC, obteniéndose expresiones analíticas con las que describir en detalle los acoplamientos generados en el sistema. Los estudios analíticos realizados se han validado experimentalmente a lo largo de la tesis. El análisis presentado en esta tesis se culmina con la obtención de un índice que condensa los márgenes de estabilidad menos conservativos. También se demuestra que la robustez del sistema está asegurada si las impedancias utilizadas en la función de sensibilidad se obtienen justamente en la entrada o la salida del subsistema que está siendo analizado. Por otra parte, la tesis presenta un conjunto de parámetros internos asimilados a impedancias, junto con sus expresiones analíticas, que permiten una explicación detallada de las interacciones en el sistema. Dichas expresiones analíticas pueden obtenerse bien mediante las funciones de transferencia analíticas si se conoce la estructura interna, o utilizando medidas en frecuencia o identificación de las mismas a través de la respuesta temporal del convertidor. De acuerdo a las metodologías presentadas en esta tesis se puede predecir la estabilidad y el comportamiento de sistemas compuestos básicamente por convertidores CC-CC y filtros, cuya estructura interna es desconocida. La predicción se basa en un índice que condensa la información de los márgenes de estabilidad y que permite la obtención de un indicador de la estabilidad global de todo el sistema, permitiendo la comparación de la estabilidad de diferentes arquitecturas de sistemas de alimentación distribuidos. ABSTRACT The purpose of this thesis is to present dynamic small-signal stability and performance analysis methodology for dc-distributed systems consisting of commercial power modules. Furthermore, the objective is to introduce simple method to state the least conservative margins for robust stability as a single number. In addition, an index characterizing the overall system stability is obtained, based on which different dc-distributed systems can be compared in terms of robustness. The interconnected systems are prone to impedance-based interactions which might lead to transient-performance degradation or even instability. These systems typically are constructed using commercial converters with unknown internal structure. Therefore, the analysis presented throughout this thesis is based on frequency responses measurable from the input and output terminals. The stability margins are stated utilizing a concept of maximum peak criteria, derived from the behavior of impedance-based sensitivity function that provides a single number to state robust stability. Using this concept, the stability information at every system interface is combined to a meaningful number to state the average robustness of the system. In addition, theoretical formulas are extracted to assess source and load side interactions in order to describe detailed couplings within the system. The presented theoretical analysis methodologies are experimentally validated throughout the thesis. In this thesis, according to the presented analysis, the least conservative stability margins are provided as a single number guaranteeing robustness. It is also shown that within the interconnected system the robust stability is ensured only if the impedance-based minor-loop gain is determined at the very input or output of each subsystem. Moreover, a complete set of impedance-type internal parameters as well as the formulas according to which the interaction sensitivity can be fully explained and analyzed, is provided. The given formulation can be utilized equally either based on measured frequency responses, time-domain identified internal parameters or extracted analytic transfer functions. Based on the analysis methodologies presented in this thesis, the stability and performance of interconnected systems consisting of converters with unknown internal structure, can be predicted. Moreover, the provided concept to assess the least conservative stability margins enables to obtain an index to state the overall robust stability of distributed power architecture and thus to compare different systems in terms of stability.

Multiphase Design and Control Techniques Applied to a Forward Micro-Inverter

En la última década la potencia instalada de energía solar fotovoltaica ha crecido una media de un 49% anual y se espera que alcance el 16%del consumo energético mundial en el año 2050. La mayor parte de estas instalaciones se corresponden con sistemas conectados a la red eléctrica y un amplio porcentaje de ellas son instalaciones domésticas o en edificios. En el mercado ya existen diferentes arquitecturas para este tipo de instalaciones, entre las que se encuentras los módulos AC. Un módulo AC consiste en un inversor, también conocido como micro-inversor, que se monta en la parte trasera de un panel o módulo fotovoltaico. Esta tecnología ofrece modularidad, redundancia y la extracción de la máxima potencia de cada panel solar de la instalación. Además, la expansión de esta tecnología posibilitará una reducción de costes asociados a las economías de escala y a la posibilidad de que el propio usuario pueda componer su propio sistema. Sin embargo, el micro-inversor debe ser capaz de proporcionar una ganancia de tensión adecuada para conectar el panel solar directamente a la red, mientras mantiene un rendimiento aceptable en un amplio rango de potencias. Asimismo, los estándares de conexión a red deber ser satisfechos y el tamaño y el tiempo de vida del micro-inversor son factores que han de tenerse siempre en cuenta. En esta tesis se propone un micro-inversor derivado de la topología “forward” controlado en el límite entre los modos de conducción continuo y discontinuo (BCM por sus siglas en inglés). El transformador de la topología propuesta mantiene la misma estructura que en el convertidor “forward” clásico y la utilización de interruptores bidireccionales en el secundario permite la conexión directa del inversor a la red. Asimismo el método de control elegido permite obtener factor de potencia cercano a la unidad con una implementación sencilla. En la tesis se presenta el principio de funcionamiento y los principales aspectos del diseño del micro-inversor propuesto. Con la idea de mantener una solución sencilla y de bajo coste, se ha seleccionado un controlador analógico que está originalmente pensado para controlar un corrector del factor de potencia en el mismo modo de conducción que el micro-inversor “forward”. La tesis presenta las principales modificaciones necesarias, con especial atención a la detección del cruce por cero de la corriente (ZCD por sus siglas en inglés) y la compatibilidad del controlador con la inclusión de un algoritmo de búsqueda del punto de máxima potencia (MPPT por sus siglas en inglés). Los resultados experimentales muestran las limitaciones de la implementación elegida e identifican al transformador como el principal contribuyente a las pérdidas del micro-inversor. El principal objetivo de esta tesis es contribuir a la aplicación de técnicas de control y diseño de sistemas multifase en micro-inversores fotovoltaicos. En esta tesis se van a considerar dos configuraciones multifase diferentes aplicadas al micro-inversor “forward” propuesto. La primera consiste en una variación con conexión paralelo-serie que permite la utilización de transformadores con una relación de vueltas baja, y por tanto bien acoplados, para conseguir una ganancia de tensión adecuada con un mejor rendimiento. Esta configuración emplea el mismo control BCM cuando la potencia extraída del panel solar es máxima. Este método de control implica que la frecuencia de conmutación se incrementa considerablemente cuando la potencia decrece, lo que compromete el rendimiento. Por lo tanto y con la intención de mantener unos bueno niveles de rendimiento ponderado, el micro-inversor funciona en modo de conducción discontinuo (DCM, por sus siglas en inglés) cuando la potencia extraía del panel solar es menor que la máxima. La segunda configuración multifase considerada en esta tesis es la aplicación de la técnica de paralelo con entrelazado. Además se han considerado dos técnicas diferentes para decidir el número de fases activas: dependiendo de la potencia continua extraída del panel solar y dependiendo de la potencia instantánea demandada por el micro-inversor. La aplicación de estas técnicas es interesante en los sistemas fotovoltaicos conectados a la red eléctrica por la posibilidad que brindan de obtener un rendimiento prácticamente plano en un amplio rango de potencia. Las configuraciones con entrelazado se controlan en DCM para evitar la necesidad de un control de corriente, lo que es importante cuando el número de fases es alto. Los núcleos adecuados para todas las configuraciones multifase consideradas se seleccionan usando el producto de áreas. Una vez seleccionados los núcleos se ha realizado un diseño detallado de cada uno de los transformadores. Con la información obtenida de los diseños y los resultados de simulación, se puede analizar el impacto que el número de transformadores utilizados tiene en el tamaño y el rendimiento de las distintas configuraciones. Los resultados de este análisis, presentado en esta tesis, se utilizan posteriormente para comparar las distintas configuraciones. Muchas otras topologías se han presentado en la literatura para abordar los diferentes aspectos a considerar en los micro-inversores, que han sido presentados anteriormente. La mayoría de estas topologías utilizan un transformador de alta frecuencia para solventar el salto de tensión y evitar problemas de seguridad y de puesta a tierra. En cualquier caso, es interesante evaluar si topologías sin aislamiento galvánico son aptas para su utilización como micro-inversores. En esta tesis se presenta una revisión de inversores con capacidad de elevar tensión, que se comparan bajo las mismas especificaciones. El objetivo es proporcionar la información necesaria para valorar si estas topologías son aplicables en los módulos AC. Las principales contribuciones de esta tesis son: • La aplicación del control BCM a un convertidor “forward” para obtener un micro-inversor de una etapa sencillo y de bajo coste. • La modificación de dicho micro-inversor con conexión paralelo-series de transformadores que permite reducir la corriente de los semiconductores y una ganancia de tensión adecuada con transformadores altamente acoplados. • La aplicación de técnicas de entrelazado y decisión de apagado de fases en la puesta en paralelo del micro-inversor “forward”. • El análisis y la comparación del efecto en el tamaño y el rendimiento del incremento del número de transformadores en las diferentes configuraciones multifase. • La eliminación de las medidas y los lazos de control de corriente en las topologías multifase con la utilización del modo de conducción discontinuo y un algoritmo MPPT sin necesidad de medida de corriente. • La recopilación y comparación bajo las mismas especificaciones de topologías inversoras con capacidad de elevar tensión, que pueden ser adecuadas para la utilización como micro-inversores. Esta tesis está estructurada en seis capítulos. El capítulo 1 presenta el marco en que se desarrolla la tesis así como el alcance de la misma. En el capítulo 2 se recopilan las topologías existentes de micro-invesores con aislamiento y aquellas sin aislamiento cuya implementación en un módulo AC es factible. Asimismo se presenta la comparación entre estas topologías bajo las mismas especificaciones. El capítulo 3 se centra en el micro-inversor “forward” que se propone originalmente en esta tesis. La aplicación de las técnicas multifase se aborda en los capítulos 4 y 5, en los que se presentan los análisis en función del número de transformadores. El capítulo está orientado a la propuesta paralelo-serie mientras que la configuración con entrelazado se analiza en el capítulo 5. Por último, en el capítulo 6 se presentan las contribuciones de esta tesis y los trabajos futuros. ABSTRACT In the last decade the photovoltaic (PV) installed power increased with an average growth of 49% per year and it is expected to cover the 16% of the global electricity consumption by 2050. Most of the installed PV power corresponds to grid-connected systems, with a significant percentage of residential installations. In these PV systems, the inverter is essential since it is the responsible of transferring into the grid the extracted power from the PV modules. Several architectures have been proposed for grid-connected residential PV systems, including the AC-module technology. An AC-module consists of an inverter, also known as micro-inverter, which is attached to a PV module. The AC-module technology offers modularity, redundancy and individual MPPT of each module. In addition, the expansion of this technology will enable the possibility of economies of scale of mass market and “plug and play” for the user, thus reducing the overall cost of the installation. However, the micro-inverter must be able to provide the required voltage boost to interface a low voltage PV module to the grid while keeping an acceptable efficiency in a wide power range. Furthermore, the quality standards must be satisfied and size and lifetime of the solutions must be always considered. In this thesis a single-stage forward micro-inverter with boundary mode operation is proposed to address the micro-inverter requirements. The transformer in the proposed topology remains as in the classic forward converter and bidirectional switches in the secondary side allows direct connection to the grid. In addition the selected control strategy allows high power factor current with a simple implementation. The operation of the topology is presented and the main design issues are introduced. With the intention to propose a simple and low-cost solution, an analog controller for a PFC operated in boundary mode is utilized. The main necessary modifications are discussed, with the focus on the zero current detection (ZCD) and the compatibility of the controller with a MPPT algorithm. The experimental results show the limitations of the selected analog controller implementation and the transformer is identified as a main losses contributor. The main objective of this thesis is to contribute in the application of control and design multiphase techniques to the PV micro-inverters. Two different multiphase configurations have been applied to the forward micro-inverter proposed in this thesis. The first one consists of a parallel-series connected variation which enables the use of low turns ratio, i.e. well coupled, transformers to achieve a proper voltage boost with an improved performance. This multiphase configuration implements BCM control at maximum load however. With this control method the switching frequency increases significantly for light load operation, thus jeopardizing the efficiency. Therefore, in order to keep acceptable weighted efficiency levels, DCM operation is selected for low power conditions. The second multiphase variation considered in this thesis is the interleaved configuration with two different phase shedding techniques: depending on the DC power extracted from the PV panel, and depending on the demanded instantaneous power. The application of interleaving techniques is interesting in PV grid-connected inverters for the possibility of flat efficiency behavior in a wide power range. The interleaved variations of the proposed forward micro-inverter are operated in DCM to avoid the current loop, which is important when the number of phases is large. The adequate transformer cores for all the multiphase configurations are selected according to the area product parameter and a detailed design of each required transformer is developed. With this information and simulation results, the impact in size and efficiency of the number of transformer used can be assessed. The considered multiphase topologies are compared in this thesis according to the results of the introduced analysis. Several other topological solutions have been proposed to solve the mentioned concerns in AC-module application. The most of these solutions use a high frequency transformer to boost the voltage and avoid grounding and safety issues. However, it is of interest to assess if the non-isolated topologies are suitable for AC-module application. In this thesis a review of transformerless step-up inverters is presented. The compiled topologies are compared using a set benchmark to provide the necessary information to assess whether non-isolated topologies are suitable for AC-module application. The main contributions of this thesis are: • The application of the boundary mode control with constant off-time to a forward converter, to obtain a simple and low-cost single-stage forward micro-inverter. • A modification of the forward micro-inverter with primary-parallel secondary-series connected transformers to reduce the current stress and improve the voltage gain with highly coupled transformers. •The application of the interleaved configuration with different phase shedding strategies to the proposed forward micro-inverter. • An analysis and comparison of the influence in size and efficiency of increasing the number of transformers in the parallel-series and interleaved multiphase configurations. • Elimination of the current loop and current measurements in the multiphase topologies by adopting DCM operation and a current sensorless MPPT. • A compilation and comparison with the same specifications of suitable non-isolated step-up inverters. This thesis is organized in six chapters. In Chapter 1 the background of single-phase PV-connected systems is discussed and the scope of the thesis is defined. Chapter 2 compiles the existing solutions for isolated micro-inverters and transformerless step-up inverters suitable for AC-module application. In addition, the most convenient non-isolated inverters are compared using a defined benchmark. Chapter 3 focuses on the originally proposed single-stage forward micro-inverter. The application of multiphase techniques is addressed in Chapter 4 and Chapter 5, and the impact in different parameters of increasing the number of phases is analyzed. In Chapter 4 an original primary-parallel secondary-series variation of the forward micro-inverter is presented, while Chapter 5 focuses on the application of the interleaved configuration. Finally, Chapter 6 discusses the contributions of the thesis and the future work.

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