Contributions to the multi-frequency control of gridtied voltage source converters

El interés por la producción de energía limpia está en aumento y la generación de este tipo de energía se puede fomentar mediante la instalación de generadores locales. Dichos generadores son conectados a la red de distribución a través de convertidores de potencia. Al mismo tiempo el número de cargas conectadas a la red está incrementando y con ello el número de cargas no lineales. Estas últimas consumen corrientes armónicas y esto provoca distorsión armónica a la red. En esta tesis se estudia y se presentan contribuciones en el control de los convertidores de potencia para que al mismo tiempo que se inyecta potencia, el convertidor sea capaz de actuar adecuadamente frente a la distorsión armónica del voltaje de la red (control multifrecuencial). En primer lugar, esta tesis cubrirá el estudio de las diferentes técnicas de control de corrientes armónicas y también de las diferentes técnicas de sincronización y detección de componentes armónicas de tensión presentes en la red. En cuanto al cálculo de referencias de corrientes armónicas, se explican las principales variantes dependiendo de la funcionalidad deseada y se estudia la entrega de potencia instantánea constante incluso con red distorsionada. Además, se propone un nuevo método de cálculo para eliminar las principales oscilaciones de potencia sin exceder las limitaciones de distorsión de corrientes. También se describen las limitaciones del convertidor cuando se trabaja con componentes fundamentales y armónicas. Se analizan los principales saturadores multifrecuenciales para evitar la sobremodulación y se propone un nuevo saturador que no empeora la dinámica total del sistema y siempre consigue el mínimo THD de corriente. Por último, se aborda la problemática de la distorsión armónica del voltaje de red. Primero se estudia la compensación de las corrientes consumidas por cargas locales y después se propone la compensación directa de la tensión del PCC. En esta tesis se intenta incrementar el número de funcionalidades que puede desempeñar el convertidor para que además de entregar potencia, sea capaz de mejorar la calidad de la red, sin exceder las limitaciones físicas del convertidor. Cada una de las contribuciones es validada mediante resultados de simulación y experimentales

Performance Improvement of Wide-Area-Monitoring-System (WAMS) and Applications Development

Wide area monitoring system (WAMS), as an application of situation awareness, provides essential information for power system monitoring, planning, operation, and control. To fully utilize WAMS in smart grid, it is important to investigate and improve its performance, and develop advanced applications based on the data from WAMS. In this dissertation, the work on improving the WAMS performance and developing advanced applications are introduced.To improve the performance of WAMS, the work includes investigation of the impacts of measurement error and the requirements of system based on WAMS, and the solutions. PMU is one of the main sensors for WAMS. The phasor and frequency estimation algorithms implemented highly influence the performance of PMUs, and therefore the WAMS. The algorithms of PMUs are reviewed in Chapter 2. To understand how the errors impact WAMS application, different applications are investigated in Chapter 3, and their requirements of accuracy are given. In chapter 4, the error model of PMUs are developed, regarding different parameters of input signals and PMU operation conditions. The factors influence of accuracy of PMUs are analyzed in Chapter 5, including both internal and external error sources. Specifically, the impacts of increase renewables are analyzed. Based on the analysis above, a novel PMU is developed in Chapter 6, including algorithm and realization. This PMU is able to provide high accurate and fast responding measurements during both steady and dynamic state. It is potential to improve the performance of WAMS. To improve the interoperability, the C37.118.2 based data communication protocol is curtailed and realized for single-phase distribution-level PMUs, which are presented in Chapter 7.WAMS-based applications are developed and introduced in Chapter 8-10. The first application is to use the spatial and temporal characterization of power system frequency for data authentication, location estimation and the detection of cyber-attack. The second application is to detect the GPS attack on the synchronized time interval. The third application is to detect the geomagnetically induced currents (GIC) resulted from GMD and EMP-E3. These applications, benefited from the novel PMU proposed in Chapter 6, can be used to enhance the security and robust of power system

Control strategy of grid connected power converter based on virtual flux approach

A la portada consta el nom del programa interuniversitari: Joint Doctoral Programme in Electric Energy Systems [by the] Universidad de Málaga, Universidad de Sevilla, Universidad del País Vasco/Euskal Erriko Unibertsitatea i Universitat Politècnica de CatalunyaDistributed Generation (DG) provides an alternative to the Centralized Generation (CG) by means of generating electricity near to the end user of power with the employment of small-scale technologies to produce electricity, mainly using Renewable Energy Sources (RES). The prospects of renewable energy integration during the next years are still very optimistic. This PhD dissertation is made to provide an alternative control framework for the grid connected power converter by adopting the virtual flux concept in the control layer. This dissertation can be divided into three main topics. The 1st topic presents the voltage sensorless control system for the grid-connected power converter. The control system presented is done without depending on AC-voltage measurement where the grid synchronization is based on the Virtual Flux (VF) estimation. In this regard, the Frequency Locked Loop (FLL) is used in conjunction with the estimation scheme to make the system fully adaptive to the frequency changes. This voltage sensorless application is useful for reducing cost and complexity of the control hardware. It is also can be utilized in case of limited reliability or availability of voltage measurements at the intended point of synchronization to the grid. Considering that most previous studies are based on the VF estimation for the case of power converter connected to the grid through the L-filter or LC-filter, this dissertation is focused on the power converter connected to the grid through the LCL filter. The Proportional Resonant (PR) current controller is adopted in the inner loop control of the power electronics-based converter to test the performance of such system. Another control method based on VF synchronization that permits to control the active and reactive power delivery in a remote point of the grid is also presented in this dissertation. This is due to the fact that the VF is implemented that the voltage in a remote point of the line can be estimated. As it will be shown in simulations and experiments, the proposed control scheme provides a good tracking and dynamic performance under step changes in the reference power. The fast synchronization and the smooth reference tracking achieved in transient conditions have demonstrated the effectiveness of the Dual Second Order Generalized Integrator controlled as Quadrature Signal Generator (DSOGI-QSG) and also the current controller used in the proposed system. In addition to the power control itself, this study could also benefit the frequency and the voltage regulation methods in distributed generation applications as for instance in microgrid. Considering the fact that the grid connected power converter can be controlled as a virtual synchronous generator where the flux is a variable to be used for controlling its operation, this dissertation also presents a Virtual Synchronous Flux Controller (VSFC) as a new control framework of the grid connected power converter. In this regard, a new control strategy in the inner loop control of the power converter will be proposed. The main components of the outer loop control of VSFC are based on the active and reactive power control. The results presented show that the VSFC works well to control the active and reactive power without considering any synchronization system. The inner loop control is able to work as it is required, and the measurement flux is able to track the reference flux without any significant delays. All the work presented in this dissertation are supported by mathematical and simulation analysis. In order to endorse the conclusions achieved, a complete experimental validations have been conducted before wrapping this dissertation with a conclusion and recommendation for future enhancement of the control strategies that have been presented.Postprint (published version

Power Converters in Power Electronics

In recent years, power converters have played an important role in power electronics technology for different applications, such as renewable energy systems, electric vehicles, pulsed power generation, and biomedical sciences. Power converters, in the realm of power electronics, are becoming essential for generating electrical power energy in various ways. This Special Issue focuses on the development of novel power converter topologies in power electronics. The topics of interest include, but are not limited to: Z-source converters; multilevel power converter topologies; switched-capacitor-based power converters; power converters for battery management systems; power converters in wireless power transfer techniques; the reliability of power conversion systems; and modulation techniques for advanced power converters

Machine Learning and Data Mining Applications in Power Systems

This Special Issue was intended as a forum to advance research and apply machine-learning and data-mining methods to facilitate the development of modern electric power systems, grids and devices, and smart grids and protection devices, as well as to develop tools for more accurate and efficient power system analysis. Conventional signal processing is no longer adequate to extract all the relevant information from distorted signals through filtering, estimation, and detection to facilitate decision-making and control actions. Machine learning algorithms, optimization techniques and efficient numerical algorithms, distributed signal processing, machine learning, data-mining statistical signal detection, and estimation may help to solve contemporary challenges in modern power systems. The increased use of digital information and control technology can improve the grid’s reliability, security, and efficiency; the dynamic optimization of grid operations; demand response; the incorporation of demand-side resources and integration of energy-efficient resources; distribution automation; and the integration of smart appliances and consumer devices. Signal processing offers the tools needed to convert measurement data to information, and to transform information into actionable intelligence. This Special Issue includes fifteen articles, authored by international research teams from several countries

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

On modeling and control of multilevel converters and PLL algorithms.

Tesis (Doctorado en Control y Sistemas Dinámicos)"The present thesis is focuses in the study of the multilevel converters and the the phaselocked loop algorithms. In the first five chapters, two of the main topologies of multilevel converters are studied, namely, diode clamped multilevel converter (NPC) and cascaded H-bridge multilevel converter (HB). First, a model is obtained that described the dynamics of the three level NPC converter used in a synchronous rectifier application. The highly nonlinear model, originally in abc-coordinates, is also expressed in its ®¯°-coordinates. Special attention is given to the °-component of the control input, which represents a degree of freedom crucial for the balancing of the capacitors voltages. Then, based on this model, it is presented an adaptive controller that guarantees regulation and balance of the output capacitors voltages, as well as a close to unity power factor. Next, the modeling and the control design processes are presented for a cascade H-bridge single-phase multilevel converter used as a shunt active filter. Crucial for the developments is the transformation of the model in terms of the sum and the difference of the squares of the capacitors voltages. Moreover, it is shown that, while the current tracking problem and the regulation problem depend on the sum of the injected voltages, the balance depends on the difference between them. It is also presented a controller for the cascade H-bridge three-phase multilevel converter used as a shunt active filter. Based on the proposed mathematical model, the controller is designed to compensate harmonic distortion and reactive power due to a nonlinear distorting load. Simultaneously, the controller guarantees regulation and balance of all capacitor voltages. The idea behind the controller is to allow distortion of the current reference during the transients to guarantee regulation and balance of the capacitors voltages. The chapters 6 and 7 of the thesis deals with the design of phase-locked loop (PLL) algorithms. Although PLLs have been widely used in many electronic applications, the PLL presented here is of special interest in the synchronization of power electronic equipment coupled with the electric network. In particular, the presented PLL has been designed to work in fixed reference frame coordinates, and thus the proposed algorithm is referred as fixed reference frame PLL (FRF-PLL).

NASA Tech Briefs, May 1996

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