UDE-based controller equipped with a multiple-time-delayed filter to improve the voltage quality of inverters

In this paper, a two-degrees-of-freedom control algorithm based on uncertainty and disturbance estimator (UDE), aimed to minimize the total harmonic distortion of inverter output voltage is proposed, possessing enhanced robustness to base frequency variations. A multiple-time-delay action is combined with a commonly utilized low-pass UDE filter to increase the range of output impedance magnitude minimization around odd multiples of base frequency for enhanced rejection of typical single-phase nonlinear loads harmonics. Marginal robustness improvement achieved by increasing the number of time delays is quantified analytically and revealed to be independent of delay order. The performance of the proposed control approach and its superiority over two recently proposed methods is validated successfully by experimental results

Contributions to Modulation and Control Algorithms for Multilevel Converters

Las actuales tendencias de la red eléctrica han lanzado a la industria a la búsqueda de sistemas de generación, distribución y consumo de energía eléctrica más eficientes. Generación distribuida, reducción de componentes pasivos, líneas DC de alta tensión son, entre otras, las posibles líneas de investigación que están actualmente siendo consideradas como el futuro de la red eléctrica. Sin embargo, nada de esto sería posible si no fuera por los avances alcanzados en el campo de la electrónica de potencia. El trabajo aquí presentado comienza con una breve introducción a la electrónica de potencia, concretamente a los convertidores de potencia conectados a red, sus estrategias de control más comunes y enfoques ante redes desbalanceadas. A continuación, las contribuciones del autor sobre el control y modulación de una topología particular de convertidores, conocidos como convertidores multinivel, se presentan como el principal contenido de este trabajo. Este tipo de convertidores mejoran la eficiencia y ciertas prestaciones, en comparación con convertidores más tradicionales, a costa de una mayor complejidad en el control al incrementar la cantidad de los componentes hardware. A pesar de que existen numerosas topologías de convertidores multinivel y algunas de ellas son brevemente expuestas en este trabajo, la mayoría de las aportaciones están enfocadas para convertidores del tipo diode-clamped converter. Adicionalmente, se incluye una aportación para convertidores del tipo multinivel modular, y otra para convertidores en cascada. Se espera que el contenido de la introducción de este trabajo, junto a las contribuciones particulares para convertidores multinivel sirva de inspiración para futuros investigadores del campo

Analysis of the Harmonic Performance of Power Converters and Electrical Drives

Power converters have progressively become the most efficient and attractive solution in recent decades in many industrial sectors, ranging from electric mobility, aerospace applications to attain better electric aircraft concepts, vast renewable energy resource integration in the transmission and distribution grid, the design of smart and efficient energy management systems, the usage of energy storage systems, and the achievement of smart grid paradigm development, among others.In order to achieve efficient solutions in this wide energy scenario, over the past few decades, considerable attention has been paid by the academia and industry in order to develop new methods to achieve power systems with maximum harmonic performance aiming for two main targets. On the one hand, the high-performance harmonic performance of power systems would lead to improvements in their power density, size and weight. This becomes critical in applications such as aerospace or electric mobility, where the power converters are on-board systems. On the other hand, current standards are becoming more and more strict in order to reduce the EMI and EMC noise, as well as meeting minimum power quality requirements (i.e., grid code standards for grid-tied power systems)

Uncertainty and disturbance estimator design to shape and reduce the output impedance of inverter

Power inverters are becoming more and more common in the modern grid. Due to their switching nature, a passive filter is installed at the inverter output. This generates high output impedance which limits the inverter ability to maintain high power quality at the inverter output. This thesis deals with an impedance shaping approach to the design of power inverter control. The Uncertainty and Disturbance Estimator (UDE) is proposed as a candidate for direct formation of the inverter output impedance. The selection of UDE is motivated by the desire for the disturbance rejection control and the tracking controller to be decoupled. It is demonstrated in the thesis that due to this fact the UDE filter design directly influences the inverter output impedance and the reference model determines the inverter internal electromotive force. It was recently shown in the literature and further emphasized in this thesis that the classic low pass frequency design of the UDE cannot estimate periodical disturbances under the constraint of finite control bandwidth. Since for a power inverter both the reference signal and the disturbance signal are of periodical nature, the classic UDE lowpass filter design does not give optimal results. A new design approach is therefore needed. The thesis develops four novel designs of the UDE filter to significantly reduce the inverter output impedance and maintain low Total Harmonic Distortion (THD) of the inverter output voltage. The first design is the based on a frequency selective filter. This filter design shows superiority in both observing and rejecting periodical disturbances over the classic low pass filter design. The second design uses a multi-band stop design to reject periodical disturbances with some uncertainty in the frequency. The third solution uses a classic low pass filter design combined with a time delay to match zero phase estimation of the disturbance at the relevant spectrum. Furthermore, this solution is combined with a resonant tracking controller to reduce the tracking steady-state error in the output voltage. The fourth solution utilizes a low-pass filter combined with multiple delays to increase the frequency robustness. This method shows superior performance over the multi-band-stop and the time delayed filter in steady-state. All the proposed methods are validated through extensive simulation and experimental results

Recent Advances in Robust Control

Robust control has been a topic of active research in the last three decades culminating in H_2/H_\infty and \mu design methods followed by research on parametric robustness, initially motivated by Kharitonov's theorem, the extension to non-linear time delay systems, and other more recent methods. The two volumes of Recent Advances in Robust Control give a selective overview of recent theoretical developments and present selected application examples. The volumes comprise 39 contributions covering various theoretical aspects as well as different application areas. The first volume covers selected problems in the theory of robust control and its application to robotic and electromechanical systems. The second volume is dedicated to special topics in robust control and problem specific solutions. Recent Advances in Robust Control will be a valuable reference for those interested in the recent theoretical advances and for researchers working in the broad field of robotics and mechatronics

Design and Control of Power Converters 2019

In this book, 20 papers focused on different fields of power electronics are gathered. Approximately half of the papers are focused on different control issues and techniques, ranging from the computer-aided design of digital compensators to more specific approaches such as fuzzy or sliding control techniques. The rest of the papers are focused on the design of novel topologies. The fields in which these controls and topologies are applied are varied: MMCs, photovoltaic systems, supercapacitors and traction systems, LEDs, wireless power transfer, etc

Mitigation of Power Quality Problems Using Custom Power Devices: A Review

Electrical power quality (EPQ) in distribution systems is a critical issue for commercial, industrial and residential applications. The new concept of advanced power electronic based Custom Power Devices (CPDs) mainly distributed static synchronous compensator (D-STATCOM), dynamic voltage restorer (DVR) and unified power quality conditioner (UPQC) have been developed due to lacking the performance of traditional compensating devices to minimize power quality disturbances. This paper presents a comprehensive review on D-STATCOM, DVR and UPQC to solve the electrical power quality problems of the distribution networks. This is intended to present a broad overview of the various possible DSTATCOM, DVR and UPQC configurations for single-phase (two wire) and three-phase (three-wire and four-wire) networks and control strategies for the compensation of various power quality disturbances. Apart from this, comprehensive explanation, comparison, and discussion on D-STATCOM, DVR, and UPQC are presented. This paper is aimed to explore a broad prospective on the status of D-STATCOMs, DVRs, and UPQCs to researchers, engineers and the community dealing with the power quality enhancement. A classified list of some latest research publications on the topic is also appended for a quick reference

Development of Grid-Connected and Front-End Converters for Renewable Energy Systems and Electric Mobility

The spread of renewable energy sources and electric vehicles is increasing thanks to the greater awareness of the climate problems due to the large and long-lasting use of the non-renewable energy sources. The integration of renewable energy sources to the power grid, however, poses significant technical challenges, since it drastically changes its topology and nature. In fact, while the traditional power generation system is centralized, the renewable energy is distributed and intermittent. In this scenario, power converters play a central role. Power converters are the technology that enables the interconnection of different players to the electric power system. In this work, a control system for grid-connected converters has been developed. The main focus is on the current control. The most renowned current controllers, such resonant and repetitive regulators, have been studied and tested in laboratory in order to compare the performance in terms of harmonic compensation and burden of the processor. The problem of the saturation of a multi-frequency current controller has been investigated and different saturation algorithms have been proposed. The power converters have, however, wide use and the same of the method, developed for grid-connected converters can be applied to electrical motor drives with open-end windings. If a floating capacitor bridge is connected to the secondary side of the open-end stator windings, it can supply the reactive power needed by the motor and completely exploit its current capability of the power source. This feature allows the drive to obtain higher torque at higher speed, increasing therefore the output power over all the flux-weakening speed range. The floating bridge, operating as harmonic compensator, allows the inverter connected to the primary energy source to work in overmodulation and even six-step modulation, in order to further boost the performance of the drive, without compromising the quality of the phase current

Modeling for harmonic analysis of ac offshore wind power plants

This Ph.D. dissertation presents the work carried out on the modeling, for harmonic analysis, of AC offshore wind power plants (OWPP). The studies presented in this Ph.D. thesis are oriented to two main aspects regarding the harmonic analysis of this type of power system. The first aspect is the modeling and validation of the main power components of an AC offshore wind power plant. Special emphasis is focused on the modeling of wind turbines, power transformers, submarine cables, and the interaction between them. A proposal of a wind turbine harmonic model is presented in this dissertation to represent the behavior of a wind turbine and its harmonics, up to 5 kHz. The distinctive structure of this model consists of implementing a voltage source containing both the fundamental component and the harmonics emitted by the converter. For the case of transformer and submarine cables, the frequency-dependent behavior of certain parameters is modeled for frequencies up to 5 kHz as well. The modeling of the frequency-dependent characteristics, due to skin and proximity effect, is achieved by means of Foster equivalent networks for time-domain simulations. Regarding the interaction between these power components, two complementary modeling approaches are presented. These are the Simulink®-based model and an analytical sequence network model of the passive components of the OWPP. A description of model development and parameterization is carried out for both modeling approaches considering a scenario that is defined according to a real offshore wind power plant. On the other hand, the second aspect of this Ph.D. thesis is oriented to the analysis of the issues that appear in offshore wind power plants in relation to harmonic amplification risk, compliance of grid codes in terms of harmonics and power factor, and the design of effective solutions to improve the harmonic emission of the facility. The technical solutions presented in this Ph.D. thesis cover aspects regarding modulation strategies, design of the connection filter of the grid side converter and management of the operation point of the grid side converter of wind turbines. This last by means of changing the setpoint of certain variables. As inferred, these are solutions from the perspective of the wind turbine manufacturer