An overview of power quality enhancement techniques applied to distributed generation in electrical distribution networks

It is obvious that power quality is an important characteristic of today's distribution power systems as loads become more sensitive on the other hand nonlinear loads are increasing in the electrical distribution system. Considering the distributed nature of harmonic loads, the need for distributed power quality improvement (PQI) is inevitable. From years ago, researchers have been working on various kinds of filters and devices to enhance the overall power quality of power system, but today the nature of distribution system has been changed and power electronic based DGs play an important role in distribution grids. In this paper, a thorough survey is done on power quality enhancement devices with emphasis on ancillary services of multi-functional DGs. A literature review is also done on microgrids concept, testbeds and related control methods. Although there were some applications of DGs for PQI improvement these applications were not defined multi-functional DGs. Various control methods are studied and categorized regarding different viewpoints in the literature. Finally, a couple of thorough comparisons are done between the available techniques considering the nature, capabilities, advantages and implementation costs

A review on power electronics technologies for power quality improvement

Nowadays, new challenges arise relating to the compensation of power quality problems, where the introduction of innovative solutions based on power electronics is of paramount importance. The evolution from conventional electrical power grids to smart grids requires the use of a large number of power electronics converters, indispensable for the integration of key technologies, such as renewable energies, electric mobility and energy storage systems, which adds importance to power quality issues. Addressing these topics, this paper presents an extensive review on power electronics technologies applied to power quality improvement, highlighting, and explaining the main phenomena associated with the occurrence of power quality problems in smart grids, their cause and effects for different activity sectors, and the main power electronics topologies for each technological solution. More specifically, the paper presents a review and classification of the main power quality problems and the respective context with the standards, a review of power quality problems related to the power production from renewables, the contextualization with solid-state transformers, electric mobility and electrical railway systems, a review of power electronics solutions to compensate the main power quality problems, as well as power electronics solutions to guarantee high levels of power quality. Relevant experimental results and exemplificative developed power electronics prototypes are also presented throughout the paper.This work has been supported by FCT-Fundação para a Ciência e Tecnologia within the R&D Units Project Scope: UIDB/00319/2020. This work has been supported by the FCT Project DAIPESEV PTDC/EEI-EEE/30382/2017 and by the FCT Project newERA4GRIDs PTDC/EEIEEE/30283/2017

A review on mitigation technologies of low frequency current ripple injected into fuel cell and a case study

© 2020 Hydrogen Energy Publications LLC This paper reviews the state-of-the-art of mitigation technologies of low frequency current ripple (LFCR) injected into fuel cell (FC). Although there are their own merits and demerits, the optimized LFCR control techniques and topology structures are characterized in many aspects like performance, durability, reliability and lifetime of FC. Three mains topologies and mitigation methods of LFCR have been investigated based on the literature review, which are the passive compensation methods, active compensation methods, and passive and active hybrid compensation methods. Some rules based tables are set to evaluate the LFCR against the topologies, control strategies, current ripple, application and advantages/limitations. Moreover, the mitigation control strategies are compared side by side with their specific applications in FC system. To select and implement them, this review can provide a reference and basis for the researchers in related fields. Finally, a case study in an uninterruptible power supply application is conducted

Control of high performance single phase DC-AC inverter

Master'sMASTER OF ENGINEERIN

Evolution of microgrids with converter-interfaced generations: Challenges and opportunities

© 2019 Elsevier Ltd Although microgrids facilitate the increased penetration of distributed generations (DGs) and improve the security of power supplies, they have some issues that need to be better understood and addressed before realising the full potential of microgrids. This paper presents a comprehensive list of challenges and opportunities supported by a literature review on the evolution of converter-based microgrids. The discussion in this paper presented with a view to establishing microgrids as distinct from the existing distribution systems. This is accomplished by, firstly, describing the challenges and benefits of using DG units in a distribution network and then those of microgrid ones. Also, the definitions, classifications and characteristics of microgrids are summarised to provide a sound basis for novice researchers to undertake ongoing research on microgrids

Decentralized control techniques applied to electric power distributed generation in microgrids

Distributed generation of electric energy has become part of the current electric power system. In this context a new scenario is arising in which small energy sources make up a new supply system: The microgrid.The most recent research projects show the technical difficulty of controlling the operation of microgrids, because they are complex systems in which several subsystems interact: energy sources, power electronic converters, energy storage systems, local, linear and non-linear loads and of course, the main grid. In next years, the electric grid will evolve from the current very centralized model toward a more distributed one. At the present time the generation, consumption and storage points are very far away one from each other. Under these circumstances, relatively frequent failures of the electric supply and important losses take place in the transport and distribution of energy, so that it can be stated that the efficiency of the supply system is low.In another context, electric companies are aiming at an electric grid, formed in a certain proportion by distributed generators, where the consumption points are near the generation points, avoiding high losses in the transmission lines and reducing the rate of shortcomings. Summing up, it is pursued the generation of small quantities of electric power by the users (this concept is called microgeneration in the origin), considering them not only as electric power consumers but also as responsible for the generation, becoming this way an integral part of the grid.In this context it is necessary to develop a new concept of flexible grid, i.e., with reconfiguration capability for operation with or without connection to the mains. The future microgrids should incorporate supervision and control systems that allow the efficient management of various kinds of energy generators, such as photovoltaic panels, energy storage systems, and local loads. Hence, we are dealing with intelligent flexible Microgrids capable of import and export power from/to the grid reconfiguring its operation modes and making decisions in real time.The researching lineas that have been introduced in this thesis are focused on the innovation in this kind of systems, the integration of several renewable energy sources, the quality of the power supply, security issues, and the system behavior during faults.In order to carry out some solutions related within these characteristics, the main goal of this thesis is the application on new control stretegies and a power management analysis of a microgrid. Thus, thanks to the emerging of renewable energy, is possible to give an alternative to the decoupling of generation units connected to the utility grid.Likewise, a work methodology has been analyzed and developed based on the modeling, control parameters design, and power management control starting from a single voltage source inverter to a number of interconnected DG units forming flexible Microgrids. In addition, all the mencioned topics have been studied giving new system performances, viability and safe functioning, thanks to the small-signal analysis and introducing control loop design algorithms, improving the import/export of electric power and operating both grid connected mode and an island.This thesis has presented an analysis, simulation and experimental results focusing on modeling, control, and analysis of DG units, giving contributions according to the following steps:- Control-oriented modeling based on active and reactive power analysis- Control synthesis based on enhanced droop control technique.- Small-signal stability study to give guidelines for properly adjusting the control system parameters according to the desired dynamic responseThis methodology has been extended to microgrids by using hierarchical control applied to droop-controlled line interactive UPSs showing that:- Droop-controlled inverters can be used in islanded microgrids.- By using multilevel control systems the microgrid can operate in both grid-connected and islanded mode, in a concept called flexible microgrid.The proposed hierarchical control required for flexible Microgrids consisted of different control levels, as following:- Primary control is based on the droop method allowing the connection of different AC sources without any intercommunication.- Secondary control avoids the voltage and frequency deviation produced by the primary control. Only low bandwidth communications are needed to perform this control level. A synchronization loop can be added in this level to transfer from islanding to grid connected modes.- Tertiary control allows the import/export of active and reactive power to the grid