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[en] ARTIFICIAL NEURAL NEYWORKS IN THE VOLTAGE CONTROL OF ELECTRICAL POWER SYSTEMS / [pt] REDES NEURAIS ARTIFICIAIS APLICADAS NO CONTROLE DE TENSÃO DE SISTEMAS ELÉTRICOS DE POTÊNCIARENATO TEIXEIRA LIMA 27 March 2008 (has links)
[pt] O controle das tensões dos diversos barramentos de um
sistema elétrico de
potência tem como objetivo garantir a qualidade da energia
fornecida aos
consumidores. As tensões devem respeitar níveis
regulamentados pelo governo.
Atualmente, no Sistema Elétrico de Potência (SEP)
brasileiro, a tarefa do controle
de tensão, realizada pelos operadores de tempo real, se
baseia nos valores e
tendências de diversas variáveis (tensões, potências
reativas e ativas, sensibilidade
dos equipamentos, dentre outras). Para a formação de um
operador nessa tarefa
são necessários de um a dois anos, tempo que poderia ser
reduzido caso um
sistema de apoio à decisão dedicado ao problema de controle
de tensão estivesse à
disposição durante o treinamento. Entretanto, em virtude do
grande número de
grandezas a serem analisadas e de suas não linearidades, é
necessário uma
ferramenta automática de apoio à decisão que seja capaz de
tratar intrinsecamente
relações não lineares. Deste modo, neste trabalho optou-se
por desenvolver um
sistema baseado em Redes Neurais Artificiais (RNA) para a
confecção do sistema
sugerido, com o objetivo de indicar a necessidade de
realizar ações de controle de
tensão utilizando-se dos recursos ou equipamentos
disponíveis. O sistema
desenvolvido é composto de três módulos: Pré-processamento;
Análise e
Classificação do evento; e Pós-processamento. Tal sistema
serve para sugerir a
manobra de equipamentos mais adequada para o controle de
tensão. No estudo de
caso, o sistema proposto foi avaliado nos equipamentos de
controle de tensão
(reatores, capacitores e tapes) constantes no Sistema de
Transmissão em 765 kV,
responsável pela interligação dos sistemas Sul e Sudeste do
Brasil. Utilizando
dados obtidos do sistema de aquisição em tempo real,
diferentes configurações de
RNAs foram testadas. Os melhores resultados foram obtidos
com uma estrutura
de duas redes neurais por equipamento a ser controlado,
apresentando, em média,
80% de acerto em relação às manobras realizadas em tempo
real. Em virtude da
complexidade do problema, os resultados foram considerados
mais do que
satisfatórios, indicando a aplicabilidade desta técnica
para a realização do sistema
desejado. / [en] The main objective of the voltage control in Electrical
Power System (EPS)
is to guarantee the quality of the energy supplied to
consumers. The voltage must
respect government regulated levels. Currently, on the
Brazilian EPS, the voltage
control task is carried out by system operators based on
diverse information, such
as current values, and trends of electric variables
(voltages, reactive and active
powers, their sensitivities in the control devices
performance, amongst others). To
fully train a operator in this task it is necessary one or
two years, period that could
be greatly reduced if a decision support system was
available during the
operator`s training. However, due to the great number of
variables that must be
analyzed and their nonlinearity, an automatic decision
support tool, capable to
treat nonlinear relations, is necessary. Therefore, this
work proposes a system
based on Artificial Neural Networks (ANN), with the
objective to identify the
necessity or not to use the voltage control resources in
the EPS. The developed
system is composed of three modules: Pre-processing; Event
Analysis and
Classification; and Post-processing. Such decision support
system suggests the
most adequate equipment maneuver in the voltage control
task. In the case study,
the proposed system was evaluated using the available
voltage control equipments
(reactors, capacitors and transformer taps) in the 765 kV
Transmission System,
main responsible trunk for the interconnection of South and
Southeastern
Brazilian systems. Using real time data, different ANN
configurations have been
tested. The best results were obtained with a structure
composed of two neural
networks, for each controlled equipment, presenting, in
average, 80% accuracy in
relation to maneuvers occurred in real time. Due to the
problem complexity, the
results were considered more than satisfactory, indicating
the applicability of this
technique for the development of the desired system.
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[en] ADEQUACY INDEXES OF VOLTAGE CONTROL ACTION FOR VOLTAGE SECURITY CONDITION REINFORCEMENT / [pt] ÍNDICES DE ADEQUAÇÃO DAS AÇÕES DE CONTROLE DE TENSÃO PARA REFORÇO DAS CONDIÇÕES DE SEGURANÇA DE TENSÃOBERNARDO HENRIQUE TODT SEELIG 07 March 2005 (has links)
[pt] A falta de recursos e a questão ecológica têm limitado a
expansão do sistema de transmissão. Esta realidade, em
conjunto com o crescimento da carga, faz com que os
sistemas elétricos trabalhem bastante carregados. Esta nova
condição pode levar a situações de colapso de tensão.
Métodos para avaliação do carregamento da rede de
transmissão tornaram-se necessários e imprescindíveis para
que se possa entender o funcionamento do sistema nestas
condições e possibilitar a sua operação de modo correto.
Ferramentas analíticas têm sido usadas para reforço das
condições de segurança de tensão do sistema em tempo real,
se for avaliado que o sistema não é suficientemente seguro.
Ações operativas de controle são determinadas, para mover o
estado do sistema para um ponto de operação seguro.
Entretanto, ferramentas de avaliação e reforço não são a
única necessidade. As mesmas ações de controle, que podem
afastar o sistema de uma situação de instabilidade de
tensão, também podem ter efeito oposto ao esperado e
contribuir para o problema, podendo até mesmo levar o
sistema ao colapso. Portanto, é necessário o
desenvolvimento de uma ferramenta computacional para avaliar
a adequação de ações de controle de tensão. Neste trabalho
é proposta uma ferramenta computacional, desenvolvida com
base no sistema linearizado das equações de fluxo de carga,
incluindo equações de controle de tensão e limites, para a
avaliação do efeito das ações de controle de tensão. São
obtidos índices que permitem avaliar se a ação de controle
é adequada ou não. Além disso, esses índices podem avaliar
a interdependência entre os controles, porque além de
indicarem o efeito do controle sobre a tensão da barra
controlada, podem indicar também o efeito do controle sobre
as outras barras de tensão controlada do sistema. Estes
índices podem ser obtidos de forma extremamente rápida, e
são adequados para uso em tempo-real. / [en] The lack of investments and the ecological matter have
limited the expansion of the transmission system. This
reality, together with the load growth, makes the electric
systems to work heavy loaded. This new condition can lead
to situations of voltage collapse. Methods for evaluation
the transmission network loading became necessary and
indispensable for understanding system performance under
these conditions and for making possible secure operation.
Analytic tools have been used to evaluate the voltage
security of the system in real time. If it is evaluated
that the system is not sufficiently secure in relation to
voltage, control actions can be determined, in order to
move the state of the system for a secure operation point.
However, these tools are not the only need. The same
control actions that can move away the system from a
situation of voltage instability, can also have opposite
effect and contribute for worsening the problem, perhaps
leading to system collapse. Therefore, it is necessary the
development of computational tools to evaluate the adequacy
of these control actions. In this work it is proposed a
computational tool, based on the linearized set of power
flow equations, including equations for voltage control and
limits, for the evaluation of the effect voltage control
actions. Indexes that allow the evaluation whether the
control action is adequate or not are obtained. The indexes
can also evaluate the interdependence among the controls,
because besides indicating the effect of the control action
on the voltage of the controlled bus, they can also
indicate the effect on the other voltage controlled buses.
The indexes can be calculated in an extremely fast way, and
are appropriate for use in real-time operation.
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Estratégia de controle de micro-redes integrando controle de tensão distribuído e programação de ganhosKäfer, Aline Thaís January 2017 (has links)
Este trabalho apresenta maneiras de trabalhar com o controle de potência reativa e estabilidade de tensão em microgrids. A estratégia de controle utilizada é o Controle por Tensão Distribuída (Distributed Voltage Control - DVC), ou controle por tensões distribuídas, um laço integral que considera as potências reativas em todas as barras como entradas e as tensões respectivas como sinais de controle. Diferentes estratégias de controle para distribuição de potência foram propostas e analisadas, sempre enfatizando seus aspectos conceituais. O cálculo dos ganhos do controlador, embora fundamental para o sucesso de qualquer estratégia de controle, geralmente não é discutido, e não são dados métodos ou linhas gerais para esta tarefa. Neste trabalho, apresentamos e discutimos diferentes metodologias para o projeto de ganhos de controle em DVC. Além disso, sendo o sistema não-linear, grandes variações de performance podem ser observadas se os mesmos ganhos de controle são usados para todos os pontos de operação, o que motiva a proposta de uma estratégia de programação de ganhos, também apresentada neste trabalho. / This text deals with the control of reactive power distribution and voltage stability in microgrids. The control strategy studied is the Distributed Voltage Control (DVC), an integral loop considering entries as reactive in every bus and the bus voltages as control signals. Different control strategies for power distribution have been proposed and analysed, always emphasising its conceptual aspects; design of the controller’s gains, however fundamental for the success of any control strategy, is usually not discussed, and no methods or guideline are given for this task. In this text we present and discuss different methodologies for tuning the control gains in DVC. Moreover, since power systems are nonlinear, large variations in performance can be observed if the same control gains are used for all operating points, which motivates the proposal of a gain scheduling strategy, also presented in here.
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Power control of single-stage PV inverter for distribution system volt-var optimizationLiu, Xiao 01 January 2013 (has links)
The output power variability of intermittent renewable sources can cause significant fluctuations in distribution system voltages. A local linear controller that exploits the capability of a photovoltaic inverter to provide both real and reactive power is described. This controller substitutes reactive power for real power when fluctuations in the output of the photovoltaic source are experienced. In this way, the inverter can help mitigate distribution system voltage fluctuations. In order to provide real and reactive to the grid, a three-phase grid-connected single-stage photovoltaic system with maximum power point tracking and power control is described. A method of reducing the current harmonic caused by resonance of the LC filter and transformer is presented. The local linear controller is examined using an example distribution system, and it is found that the controller is effective at mitigating voltage violations. The photovoltaic control system is examined using three-phase single-stage PV inverter system. The power control and damping system show good performance and stability under rapid change of irradiance.
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Estratégia de controle de micro-redes integrando controle de tensão distribuído e programação de ganhosKäfer, Aline Thaís January 2017 (has links)
Este trabalho apresenta maneiras de trabalhar com o controle de potência reativa e estabilidade de tensão em microgrids. A estratégia de controle utilizada é o Controle por Tensão Distribuída (Distributed Voltage Control - DVC), ou controle por tensões distribuídas, um laço integral que considera as potências reativas em todas as barras como entradas e as tensões respectivas como sinais de controle. Diferentes estratégias de controle para distribuição de potência foram propostas e analisadas, sempre enfatizando seus aspectos conceituais. O cálculo dos ganhos do controlador, embora fundamental para o sucesso de qualquer estratégia de controle, geralmente não é discutido, e não são dados métodos ou linhas gerais para esta tarefa. Neste trabalho, apresentamos e discutimos diferentes metodologias para o projeto de ganhos de controle em DVC. Além disso, sendo o sistema não-linear, grandes variações de performance podem ser observadas se os mesmos ganhos de controle são usados para todos os pontos de operação, o que motiva a proposta de uma estratégia de programação de ganhos, também apresentada neste trabalho. / This text deals with the control of reactive power distribution and voltage stability in microgrids. The control strategy studied is the Distributed Voltage Control (DVC), an integral loop considering entries as reactive in every bus and the bus voltages as control signals. Different control strategies for power distribution have been proposed and analysed, always emphasising its conceptual aspects; design of the controller’s gains, however fundamental for the success of any control strategy, is usually not discussed, and no methods or guideline are given for this task. In this text we present and discuss different methodologies for tuning the control gains in DVC. Moreover, since power systems are nonlinear, large variations in performance can be observed if the same control gains are used for all operating points, which motivates the proposal of a gain scheduling strategy, also presented in here.
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Estratégia de controle de micro-redes integrando controle de tensão distribuído e programação de ganhosKäfer, Aline Thaís January 2017 (has links)
Este trabalho apresenta maneiras de trabalhar com o controle de potência reativa e estabilidade de tensão em microgrids. A estratégia de controle utilizada é o Controle por Tensão Distribuída (Distributed Voltage Control - DVC), ou controle por tensões distribuídas, um laço integral que considera as potências reativas em todas as barras como entradas e as tensões respectivas como sinais de controle. Diferentes estratégias de controle para distribuição de potência foram propostas e analisadas, sempre enfatizando seus aspectos conceituais. O cálculo dos ganhos do controlador, embora fundamental para o sucesso de qualquer estratégia de controle, geralmente não é discutido, e não são dados métodos ou linhas gerais para esta tarefa. Neste trabalho, apresentamos e discutimos diferentes metodologias para o projeto de ganhos de controle em DVC. Além disso, sendo o sistema não-linear, grandes variações de performance podem ser observadas se os mesmos ganhos de controle são usados para todos os pontos de operação, o que motiva a proposta de uma estratégia de programação de ganhos, também apresentada neste trabalho. / This text deals with the control of reactive power distribution and voltage stability in microgrids. The control strategy studied is the Distributed Voltage Control (DVC), an integral loop considering entries as reactive in every bus and the bus voltages as control signals. Different control strategies for power distribution have been proposed and analysed, always emphasising its conceptual aspects; design of the controller’s gains, however fundamental for the success of any control strategy, is usually not discussed, and no methods or guideline are given for this task. In this text we present and discuss different methodologies for tuning the control gains in DVC. Moreover, since power systems are nonlinear, large variations in performance can be observed if the same control gains are used for all operating points, which motivates the proposal of a gain scheduling strategy, also presented in here.
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A heuristic optimal approach for coordinated volt/var control in distribution networksMokgonyana, Lesiba January 2015 (has links)
This dissertation focuses on daily volt/var control in distribution networks with feeder capacitors,
substation capacitors and transformers equipped with on-load tap changers. A hybrid
approach is proposed to solve the daily volt/var control problem. To reduce the computational
requirements of the problem, this approach combines two methods, namely heuristic
and optimal scheduling for the substation and feeder sub-problems respectively.
The feeder capacitor dispatch schedule is determined based on a heuristic reactive power setpoint
method. At this stage the objective is to minimize the reactive power flow through the
substation bus in every time-interval. And as such, mathematical modeling of the distribution
network components is adapted to suit time-varying conditions. Furthermore, an optimization
model to determine a proper dispatch schedule of the substation devices is formulated.
The objective of this model is to minimize the daily total energy loss and voltage deviations.
Additionally, the reference voltage of the substation secondary bus and the transformer tap
position limits are modified to adapt to given load profiles. The optimization model is solved
with a discrete particle swarm optimization algorithm, which incorporates Newton’s method
to determine the power-flow solution. The proposed method is applied to a time-varying distribution system and evaluated under
different operational scenarios. It is also compared to on-line volt/var control with various
settings. Simulation results show that the proposed approach minimizes both the voltage deviations
and the total energy loss, while on-line control prioritizes one objective over the other depending
on the specified settings. / Dissertation (MEng)--University of Pretoria, 2015. / Electrical, Electronic and Computer Engineering / Unrestricted
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A Coordinated Voltage Management Method Utilizing Battery Energy Storage Systems and Smart PV Inverters in Distribution Networks with High PV and Wind PenetrationsAlrashidi, Musaed Owehan 16 August 2021 (has links)
Electrical distribution networks face many operational challenges as various renewable distributed generation (DG), such as solar photovoltaic (PV) systems and wind, become part of their structure. Unlike conventional distribution systems, where the only unpredictable aspect is the load level, the intermittent nature of DG poses additional uncertainty levels for distribution system operators (DSO). The voltage quality problem considers the most restrictive issue that hinders high DG integration into distribution grids. Voltage deviates from the nominal grid voltage limits due to the excess power from the DG. DSOs are accustomed to improving the voltage profile by optimal adjustments of the on-load tap changers, voltage regulator taps and capacitor banks. Nevertheless, due to the frequent variability of the output energy from DG, these devices may fail in doing the needful.
Battery energy storage systems (BESS) and smart PV inverter functionalities are regarded as promising solutions to promote the seamless integration of renewable resources into distribution networks. BESS are utilized to store the surplus energy during the high penetration of renewable DG that causes high voltage levels and discharge the stored energy when the distribution grid is heavily loaded, which leads to the low voltage levels. Smart PV inverters regulate the network voltage by controlling the reactive power injection or absorption at the inverter end. This dissertation proposes a management strategy that coordinates BESS and smart PV inverter reactive power capability to improve voltage quality in the distribution systems with high PV and wind penetrations.
The proposed management method is based on a bi-level optimization algorithm consisting of upper and lower optimization levels. The proposed method determines the optimal location, capacity, numbers and BESS charging and discharging rates to support the distribution system voltage and to ensure optimal deployment of BESS. Case studies are conducted to evaluate the proposed voltage control method. The large size PV system and wind turbine impacts are studied and simulated on the modified IEEE-34 bus test feeder. In addition, the proposed method is applied to the modified IEEE low voltage test feeder to investigate the effectiveness of installing residential rooftop PV systems on the distribution system's voltage. Experimental results show promising outcomes of the proposed method in controlling the distribution networks' voltage.
In addition, a day-ahead forecast of PV power output is developed in this dissertation to assist the DSOs to accurately predict the future amounts of PV energy available and reinforcing the decision-making process of batteries operation. Hybrid forecasting models are proposed based on machine learning algorithms, which utilize support vector regression and backpropagation neural network, optimized with three metaheuristic optimization algorithms, namely Social Spider Optimization (SSO), Particle Swarm Optimization (PSO) and Cuckoo Search Optimization (CSO). These algorithms are used to improve the predictive efficacy of the selected algorithms, where the optimal selection of their hyperparameters and architectures plays a significant role in yielding precise forecasting outcomes. / Doctor of Philosophy / The need for more renewable energy has grown significantly, and many countries are embracing these technologies. However, the integration of distributed generation (DG), such as PV systems and wind turbines, poses several operational problems to the distribution system. The voltage problem represents the most significant issue that needs to be addressed. The traditional voltage control equipment may not cope with the rapid fluctuation and may impact their service life.
The continuous developments in the battery energy storage systems (BESS) and the smart PV inverter technologies result in increasing the hosting capacity of DG. BESS can store the excess power from the distributed generators and supply this energy to the grid for different operational objectives. On the other hand, the advanced PV inverter's reactive power capability can be exploited from which the grid can attain many benefits. This dissertation aims at providing a reliable control method to the voltage profile in distribution networks embedded with high PV and wind energy by optimal coordination between the operation of the BESS and the smart PV inverter.
In addition, the solar forecasting can mitigate the uncertainty associated with PV system generation. In this dissertation, the PV power forecasting application is applied in the distribution system to control the voltage. Through utilizing PV power forecasting, the decision-making for battery operation can be upheld and reinforced. The BESS can store the surplus energy from the PV system as needed and supply it back in low PV power incidents.
Experimental results indicate that proper coordination between the BESS and smart PV inverter is beneficial for distribution system operation that can seamlessly integrate PV and wind energy.
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A Data Analytics Framework for Regional Voltage ControlYang, Duotong 16 August 2017 (has links)
Modern power grids are some of the largest and most complex engineered systems. Due to economic competition and deregulation, the power systems are operated closer their security limit. When the system is operating under a heavy loading condition, the unstable voltage condition may cause a cascading outage. The voltage fluctuations are presently being further aggravated by the increasing integration of utility-scale renewable energy sources. In this regards, a fast response and reliable voltage control approach is indispensable.
The continuing success of synchrophasor has ushered in new subdomains of power system applications for real-time situational awareness, online decision support, and offline system diagnostics. The primary objective of this dissertation is to develop a data analytic based framework for regional voltage control utilizing high-speed data streams delivered from synchronized phasor measurement units. The dissertation focuses on the following three studies: The first one is centered on the development of decision-tree based voltage security assessment and control. The second one proposes an adaptive decision tree scheme using online ensemble learning to update decision model in real time. A system network partition approach is introduced in the last study. The aim of this approach is to reduce the size of training sample database and the number of control candidates for each regional voltage controller. The methodologies proposed in this dissertation are evaluated based on an open source software framework. / Ph. D.
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Derivation of Parabolic Current Control with High Precision, Fast Convergence and Extended Voltage Control ApplicationZhang, Lanhua 24 October 2016 (has links)
Current control is an important topic in modern power electronics system. For voltage source inverters, current control loop ensures the waveform quality at steady state and the fast response at transient state. To improve the current control performance, quite a few nonlinear control strategies have been presented and one well-known strategy is the hysteresis current control. It achieves fast response without stability issue and it has high control precision. However, for voltage source inverter applications, hysteresis current control has a wide switching frequency range, which introduces additional switching loss and impacts the design of harmonic filter. Other nonlinear current control strategies include one-cycle control, non-linear carrier control, peak current control, charge control, and so on. However, these control strategies are just suitable for specific topologies and it cannot be directly used by voltage source inverters.
The recently proposed parabolic current control solves the frequency variation problem of hysteresis current control by employing a pair of parabolic carriers as the control band. By the use of parabolic current control, approximate-constant switching frequency can be achieved. Due to the cycle-by-cycle control structure, it inherently has fast response speed and high precision. These advantages make it suitable for voltage source inverters, including stand-alone inverters, grid connected inverters, active power filters, and power factor correction applications.
However, parabolic current control has some limitations, such as dead-time effects, only working as bipolar PWM, complex hardware implementation, non-ideal converging speed. These problems are respectively solved in this dissertation and solutions include dead-time compensation, the implementation on dual-carrier unipolar PWM, sensorless parabolic current control, single-step current control. With the proposed dead-time compensation strategy, current control precision is improved and stable duty-cycle range are extended. Dual-carrier PWM implementation of parabolic current control has smaller harmonic filter size and lower power loss. Sensorless parabolic current control decreases the cost of system and enhances the noise immunity capability. Single-step current control pushes the convergence speed to one switching operation with simple implementation. High switching frequency is allowed and power density can be improved. Detailed analysis, motivation and experimental verification of all these innovations are covered in this dissertation.
In addition, the duality phenomenon exists in electrical circuits, such as Thevenin's theorem and Norton's theorem, capacitance and inductance. These associated pairs are called duals. The dual of parabolic current control is derived and named parabolic voltage control. Parabolic voltage control solves the audible noise problem of burst mode power converters and maintains high efficiency in the designed boost converter. / Ph. D.
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