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Utility engineers, professionals from regulatory agencies, manufacturers and researchers have discussed if high-frequency distortions produced by rooftop photovoltaic generators are a general power quality concern for distribution systems. In this context, this paper presents the results of an extensive research to investigate the emission and propagation characteristics of such high-frequency distortions. Analytical and theoretical analyses, computer simulations, laboratory experiments and field measurements revealed that high-frequency distortions emitted by rooftop photovoltaic inverters are produced with a voltage source characteristic. As a result, the equivalent grid impedance limits and attenuates significantly the high-frequency distortions injection and propagation into the distribution systems. Moreover, the front-end, low-pass filters found in many home appliances also contribute with such attenuation by sinking part of the high-frequency distortions. In summary, the results indicate that these distortions are unlikely to become a generalized power quality concern, so that the front-end filters commonly available for such devices, when properly designed, are enough to deal with this issue.

Large customers in many electric distribution utilities must enter into demand contracts for the ensuing year for defining contracted demand. Customer demand charge equals contracted demand billed at contracted tariff if the peak demand is less than the contracted demand, and, if not, the excess is billed at the uncontracted tariff. Both scenarios lead to economic loss for the customer, as the uncontracted tariff is much higher than the contracted tariff. Further, optimization of demand contracts is also important for utilities, as they plan and operate their system to satisfy customer peak demand. If under planned, it leads to technical challenges, and otherwise, it leads to economic loss. This challenge of determining the best demand to be contracted is known as the demand cost optimization problem and would save US$ 38 billion globally to customers. This work describes the problem through a graphical approach and proposes three mathematical models to find the optimum demand even in the presence of intermittent renewable generation. Each model is verified through a case study and an exhaustive study with 7,000 large customers from a Brazilian utility. The formulations are easily implementable and have the potential to assist large customers and utilities with planning studies.

Made available in DSpace on 2020-12-12T02:25:29Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-01-01 One of the impacts of harmonic resonances in wind parks is to overload wind park components. The process of identifying a problematic component may be time-consuming due to the number of scenarios and different components (capacitors, transformers, cables and generators) that must be analyzed. In this context, this paper develops a first-screening approach to narrow down the number of scenarios that must be studied in detail. It first identifies that the capacitor bank is the most critical component. Then, it uses the operating limits of the capacitor bank and the harmonic distortions measured at the wind park entrance to obtain a chart that maps the problematic operating conditions of the park. Detailed investigations are needed only if the wind park condition is in specific regions of the chart. The proposed chart is attractive for practical applications as it is obtained with a simple equation, without the need to run any computer simulation, and can be consulted with few information from the wind park that is readily available to engineers. Electrical Engineering School, Universidad de Costa Rica, 27915 San Jose, San Jose Costa Rica 11501-2060 (e-mail: andres.arguello.guillen@gmail.com) Department of Systems and Energy, University of Campinas, Campinas, Sao Paulo Brazil 13083-852 (e-mail: torquato@ieee.org) State University of Campinas, 28132 Campinas Brazil 13083-872 (e-mail: walmir@unicamp.br) Engenharia Eletrica, UNESP, Ilha Solteira Brazil 15385-000 (e-mail: padilha@dee.feis.unesp.br)

The increasing penetration of photovoltaic (PV) generators installed in low voltage networks has raised concerns about the potential impacts of these devices in overcurrent protection. As these generators are installed in a wide-scale and widely dispersed fashion in low voltage networks, they may require new study methods by utility engineers, which traditionally deal with few large synchronous generators connected at medium voltage level. To clarify whether new study methods are in fact needed or not, this paper provides a detailed analysis of the potential impacts of PV generators on the network overcurrent protection. Coordination and selectivity among circuit breaker, recloser, lateral and service transformer fuses are assessed by considering high levels of PV penetration. The full protection scheme, installed in substation, main feeder, feeder lateral, and service transformer is evaluated. Results reveal that, even under high PV penetration scenarios, the contribution of PV generators to short-circuit currents is not large enough to affect the protection scheme of the studied system.

Harmonic resonances in DFIG-based wind parks can be investigated by using extensive electromagnetic transient simulations, which is a time-consuming process. This paper shows that not all wind parks need such a detailed analysis. In response, the paper proposes a practical, easy-to-use method for a first-cut assessment of the risk of harmonic resonance of DFIG-based wind parks. First, simple equations are obtained to estimate resonance frequency and amplification in terms of wind park parameters readily available in practice. These equations reveal combinations of wind park parameters that cause problematic resonance. Such combinations are used to trace regions of concern in a chart. If the wind park is out of all regions of concern of the chart, one can directly declare this park is resonance-free, without running any simulation study. In addition to the analytic (model-based) method, a measurement-based method is provided for obtaining the resonance chart without running any simulation. Examples show how the proposed approach can be applied to facilitate resonance assessment during the wind park planning and operation.

Canada-wide climate change plans have been put in place in the form of legislation and emission reduction programs. As part of these measures, reduced amounts of natural gas can be vented, incinerated, or flared. These programs have a direct impact on the Canadian oil and gas industry. Other measures mandate the decommissioning of high-emission thermal power plants, such as coal-fired generation. At the same time, governments are encouraging the wide-scale adoption of distributed energy resources (DERs). Because of these changes, natural gas fired DERs have been proliferating in oilfields to consume the byproduct natural gas and most major oil and gas companies are diversifying their portfolio to include generation assets. It is a more sustainable and environmentally friendly scenario as compared to the previous status quo. From an electric utility standpoint, this represents a change in paradigm, because distribution systems are traditionally planned to be radial and only experience power flowing from the substation to the load centers. This change requires utilities to adapt to new concerns and requirements, which span from operation to health and safety hazards. Among these, anti-islanding is likely the most important concern to allow the safe and reliable operation of a distribution system. The standard method to avoid unintended islanded operation is the direct transfer trip. Under exceptional circumstances, the utility may waive this requirement if an alternative acceptable method is in use. This article addresses existing anti-islanding schemes and covers in detail an alternative anti-islanding method native to many inverters. This article contains the philosophy of such method and measurement results captured during commissioning of a DER containing the scheme. Furthermore, this article highlights the evolution of inverter-based generator technologies and how the revision of applicable standards (IEEE 1547) can improve the reliable operation of such DERs.

An increasing number of unstable subsynchronous resonance (SSR) has occurred for wind farms recently. These events can lead to significant loss of generation, threatening the safe operation of the system, and even damaging the generators. Accurate knowledge of SSR characteristics (SSR frequency, current magnitude, and damping) at an early stage of the event is critical for its effective mitigation. This paper proposes a method for fast and accurate identification of an SSR event and its characteristics. It takes advantage of time-stamped waveform measurements that are typically available on the terminals of series compensated transmission lines. It uses the known model of the line as a “filter” to extract the SSR components. Case studies demonstrate that the proposed algorithm can accurately compute the SSR frequency, SSR current magnitude, and damping in around one SSR cycle or less. In addition to line parameters uncertainties, the method has also proven to remain robust in the presence of harmonic distortions and reduced waveform sampling rates.

Orientador: Walmir de Freitas Filho Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação Resumo: Os impactos causados pela instalação de geradores trifásicos de médio porte (? 1 MVA) diretamente em redes primárias de distribuição de energia elétrica (com tensão ? 10 kV) têm sido intensivamente investigados nos últimos 10 anos. Por conseguinte, atualmente, práticas de análise, operação e proteção são relativamente bem definidas e aceitas. No período de amadurecimento dessa mudança de paradigma em relação à geração de energia elétrica, de forma geral os engenheiros das concessionárias analisam uma solicitação de um novo acessante por vez, emitindo um relatório sobre as necessidades ou não de alteração do projeto. Contudo, com a publicação da Resolução Normativa #482 e outras ações, verifica-se o interesse do governo brasileiro em incentivar a conexão de geração distribuída baseada em fontes renováveis (sobretudo geradores fotovoltaicos) em redes secundárias de forma intensa e extensa. Isso produz um cenário diferente do previamente investigado na maioria dos projetos de pesquisa realizados nos últimos 10 anos, criando a necessidade de novos estudos e metodologias de análise. Neste contexto, esta dissertação de mestrado apresenta uma metodologia de análise probabilística que utiliza simulações Monte Carlo para identificar o impacto agregado de múltiplos geradores fotovoltaicos. São apresentadas técnicas para modelar todas as incertezas do problema, as quais estão relacionadas principalmente com a potência produzida pelos geradores e consumida pelas cargas em cada instante do dia. São desenvolvidas também duas aplicações práticas do método de análise proposto. A primeira aplicação consiste no desenvolvimento de índices técnicos capazes de estimar de forma simples e rápida (sem realizar nenhuma simulação) a potência máxima que pode ser injetada em redes secundárias sem a ocorrência de violações técnicas. A segunda aplicação consiste em uma técnica para estimar o impacto futuro da geração fotovoltaica em determinado alimentador da concessionária, de forma a auxiliar os engenheiros no planejamento da expansão das redes de distribuição. O método de análise e as aplicações apresentadas neste trabalho podem auxiliar na redução do número de barreiras existentes para a conexão de geradores distribuídos fotovoltaicos Abstract: Impacts caused by the connection of three-phase, medium size generators (? 1 MVA) directly to primary distribution networks (with voltage ? 10 kV) have been intensively investigated over the last 10 years. As a consequence, analysis, operation and protection practices are relatively well defined and accepted. During the maturation of this paradigm change on the electric energy generation, in general, utility engineers used to evaluate new connection requests individually, providing a report with possible requirements for project modifications. However, with the publication of Normative Resolution #482 and other actions, one may notice the interest of Brazilian government on encouraging the connection of renewable-based distributed generation (mainly photovoltaic generation) to secondary distribution networks. Such fact leads to a new scenario, different from the one investigated over the last 10 years, creating the need for new studies and analysis methodologies. In such context, this M.Sc. dissertation presents a probabilistic analysis methodology that adopts Monte Carlo simulations to identify the aggregated impact of multiple photovoltaic generators. Modelling techniques are presented for all problem uncertainties, which are mainly related to the power produced by generators and consumed by loads at each instant of the day. Two practical applications of the proposed method are also developed. The first application consists in developing technical indices that provide a simple and quick estimate (without performing any simulation) of the maximum power that may be injected into secondary networks without the occurrence of technical violations. The second application consists in a technique to estimate the future impact of photovoltaic generation on a utility feeder, in order to support engineers on the expansion planning of distribution networks. The analysis methodology and applications presented in this work can help to overcome the barriers for the interconnection of photovoltaic distributed generators Mestrado Energia Elétrica Mestre em Engenharia Elétrica

In Brazil, the Electricity Regulatory Agency defines that technical losses on distribution systems must be calculated via power flow simulation, with primary and secondary systems modeled in detail. However, as this approach requires a massive amount of data not always available in practice, the agency established assumptions to enable its implementation by all Brazilian utilities. These assumptions are currently under scrutiny by the utilities. In this context, this paper investigates the assumptions regarding load connection type, load power factor, line impedance, grounding resistance and load curve resolution, to identify whether they are indeed necessary, technically sound and what is the quantitative impact on technical losses. The study was conducted on a large database with 1,248 distribution feeders modeled in OpenDSS (over 4.5 million customers) to obtain truly realistic results. Moreover, analytical derivations are presented to assess the technical correctness of all assumptions. It is found that, for the studied feeders, the assumptions seem to be reasonable, but more studies are necessary to define the load power factor and how to model reactive power compensation equipment.

A modernização das redes de distribuição de baixa tensão (BT) criou a possibilidade de conexão de novos tipos de componentes nas mesmas. Uma possibilidade atualmente considerada é a conexão de bancos de capacitores para compensação de potência reativa. Este artigo apresenta um estudo extensivo de caracterização das potenciais ressonâncias harmônicas criadas por esta conexão, considerando 66.433 redes de BT reais. Os resultados mostram que a conexão deste capacitor cria uma ressonância paralela e uma série na rede. Ambas podem ocorrer entre a 3ª e 15ª harmônicas, coincidindo com a faixa de distorções tipicamente produzidas por cargas não lineares das redes de BT. Estudos de sensibilidade são utilizados para identificar o impacto de diferentes parâmetros da rede na frequência das ressonâncias e no seu amortecimento. O estudo também mostrou que, de forma geral, a ressonância paralela apresenta maior potencial de causar problemas que a ressonância série.

Many electric distribution utilities employ series compensation to support system voltage when supplying large industrial loads located far away from the substation. Sub-synchronous resonance associated with induction motors is a well-documented phenomenon that still plague these systems and is typically handled by employing preventative measures that include sizing the series capacitor bank using rules-of-thumb. However, the maximum size of the series capacitor bank that allows the system to operate prior to creating a potential sub-synchronous resonance condition is highly dependent on the distribution system topology and induction motor parameters. As a result, these sizing practices do not prevent sub-synchronous resonance conditions in many real systems, resulting in increased number of switching operations of sub-synchronous resonance resistor insertion and of the by-pass breaker, which prevents the phenomenon but removes the series capacitor bank from the circuit when it is most needed. This paper proposes creating guidelines for sizing series capacitor banks by using practical charts derived from a large number of Electromagnetic Transient simulations. These charts can be easily adopted by utility engineers and only require basic knowledge of the distribution system and induction motor, such as Short-Circuit Ratio and motor nameplate.

The usage of Battery Energy Storage Systems (BESS) in distribution systems has been receiving increasing interest in the power industry for applications such as to improve asset loading indices, increase reliability indices through the provision of backup reserve, among others. This paper presents detailed pre-installation studies to connect a 100 kW/255 kWh BESS into a real residential LV network with high penetration of small-scale rooftop PV systems, in the context of a pilot R&D project being conducted in Brazil. Different control modes and settings and their corresponding impacts on the performance of the BESS to play some expected applications are investigated through Quasi-Static Time Series (QSTS) simulations of this network. The results obtained suggest that, if properly operated, the BESS designed has enough capacity to well-perform both grid-connected and islanded applications.

Distributed Energy Resources (DERs) have emerged as prevalent players in the energy market, driven by government subsidies, carbon tax adoption, environmental concerns, and potential utility infrastructure investment deferrals. Often, utilities must deal with technical issues arising from paradigm shifts such as large-scale adoption of DERs. One of these technical challenges is the degradation of dependability of feeder protection, which results from the short-circuit contribution from DERs connected to distribution lines. This additional fault infeed can desensitize feeder relays and slow down overcurrent elements. This paper presents measures to address this issue and quantifies their effectiveness.

An increasing number of unstable subsynchronous resonance (SSR) has occurred for wind farms recently. These events can lead to significant loss of generation, threatening the safe operation of the system, and even damaging the generators. Accurate knowledge of SSR characteristics (SSR frequency, current magnitude, and damping) at an early stage of the event is critical for its effective mitigation. This paper proposes a method for fast and accurate identification of an SSR event and its characteristics. It takes advantage of time-stamped waveform measurements that are typically available on the terminals of series compensated transmission lines. It uses the known model of the line as a "filter" to extract the SSR components. Case studies demonstrate that the proposed algorithm can accurately compute the SSR frequency, SSR current magnitude, and damping in around one SSR cycle or less. In addition to line parameters uncertainties, the method has also proven to remain robust in the presence of harmonic distortions and reduced waveform sampling rates FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP Fechado

Merchant-owned charging stations will replace gasoline stations in the near future. As charging times of electric vehicles (EV) may be significant, without optimization, customers will wait to get charged without knowing the actual period of charging. In addition, the charging facility will not be aware of optimum charging power levels and the charging time to minimize costs. In this paper, an optimal EV charging method is proposed that minimizes the total cost for a merchant-owned charging facility with multiple chargers. The formulation considers energy costs, demand charge, connected transformer capacity, charger capacities and EV power capacities. The optimal schedule for the day can be determined ahead of time such that the customers can be informed of the cost and charging schedule. This is a complex mixed-integer linear optimization challenge with three-dimensional matrices. In this paper several cases are studied using the proposed algorithm. It is fast and efficient. This methodology would be highly useful for merchant-owned EV charging facilities and it is ready for the industrial applications.

This paper presents a procedure to implement user-written models in OpenDSS for dynamic simulations using its predefined generator element and the software’s original source code in Object Pascal. The implications on the coding of a dynamic model, the internal structure and the solving algorithm sequence are addressed in order to guide the user through such process. The aforementioned is illustrated by implementing a fourth order synchronous machine as generator model and a second order hydro turbine as shaft model.

Electric vehicle (EV) charging sites in Brazil are still scarce. However, due to the large number of homes with their own garages in the country, it is believed that the growth of the technology will stimulate the use of residential charging stations (CSs). Because the EV is a load with significant power consumption and remains connected to the grid for several hours during its slow recharge, this article aims to analyze and identify the possible impacts associated with this condition from the point of view of the power grid and the electricity utility company and its influence on the power quality of low voltage urban networks. Therefore, real field measurements are used and analyzed according to Brazilian and international recommendations and standards.

O aumento na adocao de veiculos eletricos (VEs) acarretou no desenvolvimento de uma intrincada infraestrutura de recarga em paises europeus, E.U.A. e China. Tal infraestrutura consiste em eletropostos do tipo lento, semirrapido e rapido, os quais apresentam caracteristicas eletricas e comportamentais especificas. As ferramentas de simulacao existentes atualmente nao sao suficientemente abrangentes para integrar as caracteristicas da recarga do VE, alem de nao modelarem detalhadamente os fatores comportamentais para investigar os impactos tecnicos em redes de distribuicao. Neste contexto, este artigo propoe um metodo de simulacao estocastico serie temporal (baseado no metodo de Monte Carlo) capaz de englobar as caracteristicas eletricas e comportamentais de todos os tipos de eletropostos existentes. Estudos extensivos em uma rede real brasileira destacaram os impactos individuais e combinados em ambas as redes primarias e secundarias. Adicionalmente, os resultados permitiram identificar qual tipo de eletroposto tem maior influencia sobre o perfil de tensao da rede. Este tipo de informacao pode ajudar as concessionarias a antecipar impactos tecnicos em seu sistema.

Stray voltages have always been a concern to utility companies and customers. But methods to troubleshoot and monitor nonroutine stray voltage problems are very limited. This paper presents a passive, measurement-based method to identify the contributors to the common cause of stray voltages, the neutral-to-earth voltage (NEV) rise at the service entrance point. The paper shows that the NEV can be decoupled into two components: those related to the customer under investigation and those outside the customer facility. A method to quantify the relative contributions of the two components is proposed. A new concept called current return ratio is introduced to facilitate the decoupling and to quantify the grounding conditions of the system. This paper presents the background, circuit model, concept, and theory of the proposed method.

The method to identify the sources of the neutral-to- earth voltage (NEV) rise as presented in a companion paper is verified in this paper through extensive simulation studies and field measurements. Sensitivity studies are conducted to determine factors that affect the performance of the proposed method. The results show that the NEV contribution factor index is effective in identifying load unbalance caused NEV and its contributors. The current return ratio index is effective in diagnosing poor grounding caused NEV and its contributors. An NEV trouble shooting strategy and a system-wide NEV condition monitoring strategy are proposed based on the findings.

This paper proposes an algorithm to develop an optimum Electric Vehicle (EV) charging schedule for a charging facility with a single charger. Although there are many researches to address the developing of an optimum schedule for EV charging, current methods do not address this problem from the charging facility owner's perspective. We use a hybrid system framework to capture the tradeoff between demand charges proportional to the peak demand and speed of charging. However, this hybrid framework leads to a nonconvex and non-differentiable problem. This challenge is overcome by decomposing the problem into multiple smaller and simpler constrained convex optimization problems. With the resulting convex model proposed here, the minimum cost day ahead EV charging schedule can be determined from the charging facility owner's perspective. By using this tool, a day ahead, charging facility owner has the ability to set up prices based on the cost and customer has the ability to know the prices, the total waiting and the charging time at the charging facility. The nonlinear cost optimization model was developed by using a backward recursive algorithm. The proposed algorithm has been analyzed for different penalty factors which were imposed on total waiting time of each EV. Final results are analyzed and discussed.

This paper provides a comprehensive analysis of the energy storage (ES) potential to mitigate technical impacts caused by the increased penetration of photovoltaic generators and electric vehicles in distribution networks. A Monte Carlo simulation strategy is first proposed to perform such study. ES impact on voltage magnitude/unbalance, conductor/transformer loading and technical losses is investigated in detail. Then, a study is carried out to determine whether dispersed (on customers) or concentrated (on transformers) ES allocation practices are more advantageous. Results show that ES generally has positive impacts on network operation, although its impacts can become negative once ES adoption rates become extreme (i.e., approaching 100%). Furthermore, it is found to be generally advantageous to install ESs within customers premises, rather than to install these devices on service transformers. This work is intended to support the development of attractive methods to integrate ES into distribution networks.

Latest generations of streetlights have been designed to support and integrate a number of features conducive to Smart Cities. LED streetlights now contain sensors, controls, wireless transmitters and microprocessors. These streetlights are gaining popularity and being deployed in large scale, eventually replacing all lighting throughout a city. The general conception is that electronic loads are harmonic sources, which can disturb the operation and supply of an electric utility. It is important for utilities to understand the true impact of this conversion program on the Power Quality. This paper studies the harmonic characteristics of LED streetlights on both individual and collective scales. On an individual level, the harmonic signature of several types of modern LED streetlights are collected and reported. On a collective level, a real case study of a large-scale deployment is studied. Real measurement data were collected during the streetlight conversion program in the city of Fort McMurray to analyze the impact on background harmonic voltage distortion. Results have shown it is unlikely LED streetlights will affect significantly the network voltage and current distortions.

Orientador: Walmir de Freitas Filho Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação Resumo: Os sistemas modernos de distribuição de energia elétrica (SMDEE) estão migrando de uma estrutura passiva, não supervisionada para uma estrutura ativa e supervisionada devido à integração de geradores distribuídos, dispositivos de medição e monitoramento distribuídos, novas classes de cargas tais como veículos elétricos e eletrodomésticos modernos baseados em eletrônica de potência, e dispositivos de armazenamento de energia. Estas mudanças não estão restritas ao sistema da concessionária (e.g., monitoramento extensivo da rede), mas se estendem também aos dispositivos utilizados pelo consumidor final (e.g., eletrodomésticos modernos baseados em eletrônica de potência, geradores fotovoltaicos, veículos elétricos). Apesar das diversas vantagens técnicas (e.g., redução das perdas, melhoria da eficiência energética) e ambientais (e.g., redução da poluição atmosférica), estes desenvolvimentos têm o potencial de criar vários novos impactos na qualidade de energia elétrica (QEE) dos sistemas de distribuição. Este cenário tem atraído atenção das concessionárias de distribuição ao redor do mundo, especialmente devido à falta de informação de como avaliar e gerenciar estes novos impactos na QEE. Neste contexto, o principal objetivo desta tese de doutorado é investigar de forma detalhada dois novos impactos na QEE: o impacto do aumento excessivo da tensão neutro-terra no painel de entrada do consumidor e das distorções de alta frequência no sistema de distribuição. Um método passivo, baseado em medições, é desenvolvido para determinar os fatores que contribuem para o aumento da tensão neutro-terra do consumidor (a maior causa de incidentes relativos a stray voltage). O método proposto apresenta três vantagens principais em relação a métodos existentes. Primeira, o teste pode ser realizado sem a necessidade de manipular (chavear) nenhuma carga e, portanto, sem causar nenhum inconveniente ao consumidor. Segunda, os resultados obtidos podem ser empregados para monitorar a qualidade do sistema de aterramento envolvido, tais como neutro interrompido e aterramento de má qualidade no consumidor. Terceira, o método dispensa a necessidade de medir as tensões de neutro e, portanto, é possível eliminar a difícil tarefa de estabelecer um ponto de referência para a tensão. Com relação às distorções de alta frequência (DAF), foram conduzidos estudos analíticos, simulações computacionais, experimentos em laboratório e medições em campo a fim de fornecer, para a comunidade científica e para as concessionárias de distribuição, um entendimento detalhado do comportamento das distorções de alta frequência e de sua propagação pela rede da concessionária. Adicionalmente, um circuito equivalente capaz de modelar as DAF é proposto, validado e empregado para analisar alguns fenômenos relacionados à propagação das DAF. Estes estudos referentes às distorções de alta frequência são realizados considerando-se principalmente DAF produzidas por inversores presentes em geradores fotovoltaicos Abstract: Modern power distribution systems (MPDS) are migrating from a passive, non-supervised structure to an active, supervised structure due to the integration of distributed generators, distributed metering and monitoring devices, new types of loads, such as electrical vehicles and modern electronic appliances, and energy storage devices. Such changes are not limited to the utility system (e.g., extensive network monitoring), but are also extended to customer devices (e.g., modern power electronic based appliances, photovoltaic generators, electric vehicles). In spite of many technical (e.g., loss reduction, energy efficiency improvement) and environmental (e.g., reduction on air pollution) advantages, these developments may potentially create a number of new adverse power quality (PQ) impacts on distribution systems. This scenario has attracted the attention of distribution utilities around the world, especially due to the lack of information on how to evaluate and manage these new PQ concerns. In such context, the main goal of this PhD thesis is to investigate in detail two new PQ concerns: the impact of excessive neutral-to-earth voltage rise at customer service panel and of high frequency waveform distortions on distribution systems. A passive, measurement-based, method for determining the contributors to a customer¿s neutral-to-earth voltage (the main cause of stray voltage incidents) has been developed. The proposed method has three main advantages over existing methods. First, the test can be performed without switching off any load and, therefore, without causing inconvenience to the customer. Second, the obtained results can be employed to monitor the grounding conditions of the system involved, such as broken neutral and poor customer grounding. Third, the method does not require measuring neutral voltages and, therefore, the difficult task of establishing a voltage reference point is eliminated. Regarding the high frequency distortions (HFD), analytical studies, computer simulations, lab experiments and field measurements have been conducted to provide the scientific community and distribution utilities with a comprehensive understanding of the behavior of high frequency waveform distortions and of their propagation characteristics into the utility grid. Furthermore, an equivalent circuit model is proposed, validated, and subsequently employed to analyze some of the phenomena associated with HFD propagation. These studies associated with high frequency waveform distortions are conducted mainly with HFD emitted by inverters found in photovoltaic generators Doutorado Energia Elétrica Doutor em Engenharia Elétrica FAPESP 2014/09538-6, 2016/20157-0 CNPQ

This paper presents a probabilistic harmonic simulation method to study the power-quality impact of electric vehicles (EVs). The proposed method takes into account the random operating characteristics of the vehicles, such as random charging time, charging duration, and vehicle locations. A multiphase model of the primary and secondary systems is used to represent the study system. Extensive case studies have been conducted using the method and the measured EV data. The results reveal that the current versions of plug-in hybrid EVs have no significant harmonic impact on power systems. However, the Level 1 charger can increase the neutral-to-earth voltage at homes which could lead to increased stray voltage incidents.

This paper studies the impact of different plug-in electric vehicles on network harmonic distortions, both at low frequencies and at high frequencies. Extensive measurements have been conducted in four different EVs (both regular passenger vehicles and electric buses), charged through different stations. Fast and slow, commercial and residential charging events were monitored. The collected set of measurements has shown that EV charging does have an impact on harmonic distortion levels. At low frequencies, harmonic voltages are below 4.0% and, therefore, EV impact is limited and unlikely to cause violations of harmonic distortion limits established in the Brazilian regulation (i.e., 10%). At high frequencies, voltage distortions of up to 1.0% of 60 Hz voltage were observed; however, the results are still preliminary and do not offer a reliable conclusion on whether such distortions have the potential to become a concern for utilities or not.

The operation of modern power electronic switches located in photovoltaic (PV) inverters have the potential to create high frequency harmonic (HFH) distortions. This paper investigates the emission of such distortions by PV inverters installed in a Brazilian solar farm. High-resolution measurements are performed on three different commercial inverters, with 15 kVA rated capacity each. Results obtained from the specific measurements presented in this paper reveal HFH current distortions may reach up to 2% of fundamental frequency current, whereas HFH voltages remain below 0.2% of fundamental frequency voltage. Therefore, results suggest HFH distortions emitted by these specific PV inverters are unlikely to cause significant problems to the utility.

The method to identify the sources of the neutral-to-earth voltage (NEV) rise as presented in a companion paper is verified in this paper through extensive simulation studies and field measurements. Sensitivity studies are conducted to determine factors that affect the performance of the proposed method. The results show that the NEV contribution factor index is effective in identifying load unbalance caused NEV and its contributors. The current return ratio index is effective in diagnosing poor grounding caused NEV and its contributors. An NEV troubleshooting strategy and a system-wide NEV condition monitoring strategy are proposed based on the findings.

High-frequency harmonics produced by modern switched mode power supplies have attracted attention in research community recently. To clarify if these harmonics are indeed a potential power quality concern, a research work has been conducted to understand the propagation characteristics of the harmonics. Through field measurements and computer simulations, the research found that the high-frequency harmonics are attenuated significantly when traveling from the source location to the primary distribution system. In addition, various front-end filters of home appliances can further reduce high-frequency harmonics through shunt filtering. It was also found that these distortions are unlikely to deteriorate the reliability of Power Line Communication. The main conclusion drawn from the findings is that high-frequency harmonics produced by home appliances or other low voltage devices are unlikely to cause general power quality problems, if they have proper front-end filters that are commonly available for such devices.

With the publication of resolution #482/2012 by the Brazilian Electricity Regulatory Agency (ANEEL), the penetration of small-scale photovoltaic (PV) generators has started to increase rapidly in Brazil. This trend will reduce the total energy consumed by customers from the utility. Therefore, traditional techniques used by distribution utilities for long-term energy planning (1 to 5-year horizon) must be updated to include PV generation impact. In response, this paper proposes a Monte Carlo based methodology for the long-term energy planning of distribution utilities, taking into account the probabilistic aspects of PV penetration growth. However, if simulations are conducted with high resolutions (e.g. 1-minute resolution) the time required to run all simulations may be excessive. To overcome this issue, an analysis of the data granularity impact on results precision is presented. It is observed that 1 “average day”, described using 1-hour data resolution, is sufficient to provide a good and quick estimate of the PV generation impact on long-term energy planning.

This paper proposes a real-time Energy Management System (EMS) for a low voltage (LV) Microgrid (MG). The system operation consists in solving the Unit Commitment (UC) and Economic Load Dispatch (ELD) simultaneously for 24 hours ahead at every 15-minute period. This operation is formulated as a multi-objective optimization problem where the minimization of operational cost, total emissions and power losses is simultaneously pursued using the Non-dominated Sorting Genetic Algorithm II (NSGA-II). In this algorithm, crossover and mutation operators were improved with respect to existing approaches to achieve an adequate characterization of the energy management problem and a good algorithm performance. Simulation studies have outlined that, in fact, the NSGA-II can be used as a real-time optimization tool providing a good-quality Pareto front to operate optimally the MG in a limited time of 15 minutes.

The increasing adoption of plug-in electric vehicles (EVs) on the market has raised a concern about the technical impacts this massive connection scenario may bring to the grid. In response to such concern, this paper presents a comprehensive analysis of plug-in EV charging impact on distribution networks. Three aspects of EV connection are addressed. Firstly, residential penetration is considered and its main technical impacts are identified. The second aspect is the use of charging stations; its operation impacts are compared with residential connections and advantages/drawbacks are pointed out. Finally, a smart vehicle-to-grid (V2G) operation mode is introduced. It is shown that, under a time-dependent tariff scenario, such operation mode is highly attractive to the EV owner, as the revenue arisen from power injection may compensate EV charging expenses, approaching a zero fuel expense vehicle. In addition, it is shown that smart V2G operation greatly increases the system load factor.

This paper proposes two novel algorithms to detect appliance switch-ON/OFF events, which is the first key step of a Nonintrusive Load Monitoring (NILM) software. The Window with Margins method uses the left and right margins of a window running over the house power consumption curve to locate power steps, while the Shifted Sample method relies on the derivative of the power consumption curve to identify power steps. The former may achieve higher event detection rates, while the latter presents very low complexity and requires a reduced computational effort. Extensive sensitivity studies were performed with the parameters of each method, and obtained results have shown the importance of an adequate parameter setting, as successful event identification rates may be increased up to 95%. The applicability and effectiveness of such algorithms have been verified using field measurement data.

In Brazil, in spite of the outstanding solar irradiance levels, the installed amount of photovoltaic (PV) generation was practically inexistent until two years ago. This scenario started to change with the publication of resolution #482/2012 by the Brazilian Electricity Regulatory Agency, which establishes the main technical and commercial rules for residential power generation. This paper presents an overview of the current and near future scenarios of residential PV generation in Brazil, including regulatory aspects. The largest Brazilian field project on PV integration (about to start in 2014) is described. Since PV arrays use power electronic inverters, the imminence of a high PV penetration has raised utilities attention to its potential impacts on system harmonic distortion levels. In such context, this paper also identifies, through extensive simulations, the key factors influencing PV impacts on harmonic distortion level. It is found that the most important factors are: network loading level; PV connection point; and PV power factor.

Technological development, energy source diversification, environment concerns, financial incentives have driven the increasing interest on the interconnection of small scale distributed generators (SSDG) into low voltage (LV) distribution networks. This practice allows homeowners and others to contribute to the energetic matrix without having to implement expensive modifications to the grid. In this context, this paper presents a review of the requirements adopted by distribution companies worldwide to facilitate the connection of SSDG units while maintaining the integrity of the public low voltage distribution network, both in terms of safety and supply quality. Issues like disconnect switch, protection, metering, and power quality are examined.