214 research outputs found
Bio inspired techniques for simultaneous design of multiple optimal power system stabilizers
Bio-inspired techniques are fields of study that are inspired from topics of connectionism, social behavior and emergence. Researchers have ventured into the intricacies involved with the techniques and devised algorithms based on their study. Such techniques are the focus of this thesis. The two bio-inspired techniques used for simultaneous design of power system stabilizers (PSSs) in this study are - Particle Swam Optimization (PSO) and Bacteria Foraging Algorithm (BFA). The work in this thesis is presented in three papers as follows: Paper 1 -This paper introduces an improved PSO called Small Population based PSO (SPPSO) with less number of particles and unique regeneration concept. The efficacy of the algorithm is evaluated for the simultaneous design of power system stabilizers (PSSs) on the two-area and 16 machine power systems. Paper 2 - The second paper presents a new algorithm - Bacterial Foraging Algorithm (BFA) for simultaneous tuning of multiple PSSs on a 16 machine power system. The variants of the BFA like the run length and the swarming are explored for better performance for two different design techniques and the results are compared. Paper 3 - The third paper compares SPPSO and BFA towards simultaneous tuning of multiple PSSs on two-area and Nigerian power system. This paper presents both algorithms as a first step towards online optimization and proposes to implement these algorithms in real power systems in near future --Abstract, page iv
Speed control of an SPMSM using a tracking differentiator-PID controller scheme with a genetic algorithm
In this paper, a tracking differentiator-proportional integral and derivative (TD-PID) control scheme is proposed to control the speed of a surface mount permanent magnet synchronous motor (SPMSM). The TD is used to generate the necessary transient profile for both the reference and the output speed, which are compared with each other to produce the error signals that feed into the PID controller. In addition to the TD unit parameters, the PID controller’s parameters are tuned to achieve the optimum new multi-objective performance index, comprised of the integral of the time absolute error (ITAE), the absolute square of the control energy signal (USQR), and the absolute value of the control energy signal (UABS) and utilizing a genetic algorithm (GA). A nonlinear model of the SPMSM is considered in the design and the performance of the proposed TD-PID scheme was validated by comparing its performance with that of a traditional PI controller in a MATLAB environment. Different case studies were tested to show the effectiveness of the proposed scheme, results including peak overshoot, energy consumption, control signal chatter, and 30% improvement in the OPI, with variable reference speeds, load torque, and parameters uncertainties. Illustrate the proposed scheme's success compared with PI controller
Grid-forming wind power plants
With growing concerns over climate change, the power system is witnessing an unprecedented growth in electricity generation from intermittent renewable energy sources (RES) such as wind and solar, which are commonly interfaced to the grid by power-electronic converters. However, increasing the penetration level of converter-interfaced generation units reduces the number of synchronous generators (SGs) in the grid that provide system services to support voltage and frequency, either inherently or through mandatory requirements and market products. This brings several challenges for the grid operators, which include increasing risk of harmonic interactions, decreasing system inertia and reduction in the short-circuit power of the grid, which all together might jeopardize the security and availability of the power systems. As a countermeasure, it is necessary that the power-electronic-based generation units not only provide grid support services that are originally provided by the SGs, but also operate in harmony with other generation units in all kinds of grid conditions. As a result, the concept of grid-forming (GFM) control, which mimics the beneficial properties of the SGs in converter systems, has emerged as a viable solution to allow effective and secured operation of power systems with increased penetration of converter-based resources.\ua0\ua0 This thesis investigates the application of GFM control strategies in wind power plants (WPPs). In particular, the focus of the work will be on developing an effective GFM control strategy for the energy storage systems (ESS) in WPPs that not only supports the operation of the WPP in various grid conditions, but also offers a certain degree of GFM properties to the overall WPP. To start with, the selection of the most suitable GFM control strategy for wind power applications is made by evaluating and comparing various control strategies available in the literature. The comparison is based on their influence on the frequency characteristics of the converter and robustness of the controller in varying grid strength. To address the transient stability problem of GFM converters during current limitation, a novel strategy based on the limitation of converter\u27s internal voltage vector is developed, which effectively limits the converter current to a desired value and retains the GFM properties of the converter at all times. An experimental setup is used to validate the effectiveness of the proposed limitation strategy in case of various grid disturbances. By implementing the proposed GFM control strategy for the ESS in a test WPP model, it is shown using detailed time-domain simulation results that the GFM behaviour can be offered to the overall WPP. The Network Frequency Perturbation (NFP) plots are used to verify the GFM behaviour of the considered WPP. Furthermore, an overview of various energy storage technologies (ESTs) suitable for providing ancillary services from WPPs is presented. With a focus on the two most suitable ESTs, i.e., batteries and supercapacitors, recommendations are given for design and sizing of the ESS for a given application. Finally, a coordinated control strategy between the WPP and SGs is developed, which facilitates the provision of frequency support from the WPP and at the same time reduces the energy storage requirements for the converter system
Novel control design and strategy for load frequency control in restructured power systems
In restructured electric power systems, a number of generation companies and independent power producers compete in the energy market to make a profit. Furthermore, a new marketplace for ancillary services is established, providing an additional profit opportunity for those power suppliers. These services are essential since they help support the transmission of power from energy sources to loads, and maintain reliable operation of the overall system. This dissertation addresses regulation , a major ancillary service also known as the load frequency control (LFC) problem, and presents novel control designs and strategies for the LFC in restructured power systems.;A power system is an interconnection of control areas, which are operated according to control performance standards established by the North American Electric Reliability Council (NERC). LFC is a necessary mechanism in each control area because it maintains a balance between power demand and power generation while assuring compliance with NERC standards.;This dissertation first develops three new control designs that yield effective and robust load frequency control actions. All controllers developed here require only local measurements. The first control design is based on decoupling each area thru modeling of the interconnection effects of other control areas. The second control design relies on the robust H infinity theory in terms of linear matrix inequalities (LMIs). The third control design is achieved by the collaboration between genetic algorithms (GAs) and LMIs. The first two control designs result in high-order dynamic controllers. The third design requires only a simple proportional-integral (PI) controller while yielding control performance as good as those resulting from the previous two designs. Consequently, the third control design is the most preferable due to its simplicity and suitability for industry practice. Furthermore, a stability analysis method based on perturbation theory of eigenvalues is developed to assess the stability of the entire power system being equipped by the proposed controllers.;Second, to comply with NERC standards, two LFC strategies are developed to direct LFC\u27s actions. One strategy employs fuzzy logic to mimic a skillful operator\u27s actions so that all decisions are made efficiently. The other strategy treats the compliance with NERC standards as constraints while minimizing the operational and maintenance costs associated with LFC actions. Three new indices are introduced to assess economic benefits from the strategy compared to the conventional methods. Simulation is performed to demonstrate performances of all proposed methods and strategies
Optimization-based Fast-frequency Support in Low Inertia Power Systems
The future electrical energy demand will largely be met by non-synchronous renewable energy sources (RESs) in the form of photovoltaics and wind energy. The lack of inertial response from these non-synchronous, inverter-based generation in microgrids makes the system vulnerable to large rate-of-change-of-frequency (ROCOF) and frequency excursions. This can trigger under frequency load shedding and cause cascaded outages which may ultimately lead to total blackouts. To limit the ROCOF and the frequency excursions, fast-frequency support can be provided through appropriate control of energy storage systems (ESSs). For proper deployment of such fast-frequency control strategies, accurate information regarding the inertial response of the microgrid is required. In this dissertation, a moving horizon estimation (MHE)-based approach is first proposed for online estimation of inertia and damping constants of a low-inertia microgrid. The MHE also provides real estimates of the noisy frequency and ROCOF measurements. The estimates are employed by a model predictive control (MPC) algorithm that computes control actions to provide fast-frequency support by solving a finite-horizon, online optimization problem. The combined MHE-MPC framework allows an ESS operator to provide near-optimal fast-frequency support as a service. The framework maintains the desired quality-of-service (limiting the ROCOF and frequency) while taking into account the ESS lifetime and physical limits. Additionally, this approach avoids oscillatory behavior induced by delays that are common when using low pass filter and traditional derivative-based (virtual inertia) controllers with high gains. Through simulation results, it has been shown that the proposed framework can provide near-optimal fast-frequency support while incorporating the physical limits of the ESS. The MHE estimator provides accurate state and parameter estimates that help in improving the dynamic performance of the controller compared to traditional derivative-based controllers. Furthermore, the flexibility of the proposed approach to achieve desired system dynamics based on the desired quality-of-service has also been demonstrated
Control of AC/DC microgrids with renewables in the context of smart grids including ancillary services and electric mobility
Microgrids are a very good solution for current problems raised by the constant growth
of load demand and high penetration of renewable energy sources, that results in grid
modernization through “Smart-Grids” concept. The impact of distributed energy sources
based on power electronics is an important concern for power systems, where natural
frequency regulation for the system is hindered because of inertia reduction. In this context,
Direct Current (DC) grids are considered a relevant solution, since the DC nature of power
electronic devices bring technological and economical advantages compared to Alternative
Current (AC). The thesis proposes the design and control of a hybrid AC/DC Microgrid
to integrate different renewable sources, including solar power and braking energy recovery
from trains, to energy storage systems as batteries and supercapacitors and to loads like
electric vehicles or another grids (either AC or DC), for reliable operation and stability.
The stabilization of the Microgrid buses’ voltages and the provision of ancillary services
is assured by the proposed control strategy, where a rigorous stability study is made.
A low-level distributed nonlinear controller, based on “System-of-Systems” approach is
developed for proper operation of the whole Microgrid. A supercapacitor is applied to
deal with transients, balancing the DC bus of the Microgrid and absorbing the energy
injected by intermittent and possibly strong energy sources as energy recovery from the
braking of trains and subways, while the battery realizes the power flow in long term.
Dynamical feedback control based on singular perturbation analysis is developed for
supercapacitor and train. A Lyapunov function is built considering the interconnected
devices of the Microgrid to ensure the stability of the whole system. Simulations highlight
the performance of the proposed control with parametric robustness tests and a comparison
with traditional linear controller. The Virtual Synchronous Machine (VSM) approach is
implemented in the Microgrid for power sharing and frequency stability improvement. An
adaptive virtual inertia is proposed, then the inertia constant becomes a system’s state
variable that can be designed to improve frequency stability and inertial support, where
stability analysis is carried out. Therefore, the VSM is the link between DC and AC side
of the Microgrid, regarding the available power in DC grid, applied for ancillary services
in the AC Microgrid. Simulation results show the effectiveness of the proposed adaptive
inertia, where a comparison with droop and standard control techniques is conducted.As Microrredes são uma ótima solução para os problemas atuais gerados pelo constante crescimento
da demanda de carga e alta penetração de fontes de energia renováveis, que resulta na modernização
da rede através do conceito “Smart-Grids”. O impacto das fontes de energia distribuídas baseados
em eletrônica de potência é uma preocupação importante para o sistemas de potência, onde a
regulação natural da frequência do sistema é prejudicada devido à redução da inércia. Nesse
contexto, as redes de corrente contínua (CC) são consideradas um progresso, já que a natureza
CC dos dispositivos eletrônicos traz vantagens tecnológicas e econômicas em comparação com a
corrente alternada (CA). A tese propõe o controle de uma Microrrede híbrida CA/CC para integrar
diferentes fontes renováveis, incluindo geração solar e frenagem regenerativa de trens, sistemas de
armazenamento de energia como baterias e supercapacitores e cargas como veículos elétricos ou
outras (CA ou CC) para confiabilidade da operação e estabilidade. A regulação das tensões dos
barramentos da Microrrede e a prestação de serviços anciliares são garantidas pela estratégia
de controle proposta, onde é realizado um rigoroso estudo de estabilidade. Um controlador não
linear distribuído de baixo nível, baseado na abordagem “System-of-Systems”, é desenvolvido para
a operação adequada de toda a rede elétrica. Um supercapacitor é aplicado para lidar com os
transitórios, equilibrando o barramento CC da Microrrede, absorvendo a energia injetada por fontes
de energia intermitentes e possivelmente fortes como recuperação de energia da frenagem de trens
e metrôs, enquanto a bateria realiza o fluxo de potência a longo prazo. O controle por dynamical
feedback baseado numa análise de singular perturbation é desenvolvido para o supercapacitor e
o trem. Funções de Lyapunov são construídas considerando os dispositivos interconectados da
Microrrede para garantir a estabilidade de todo o sistema. As simulações destacam o desempenho
do controle proposto com testes de robustez paramétricos e uma comparação com o controlador
linear tradicional. O esquema de máquina síncrona virtual (VSM) é implementado na Microrrede
para compartilhamento de potência e melhoria da estabilidade de frequência. Então é proposto o
uso de inércia virtual adaptativa, no qual a constante de inércia se torna variável de estado do
sistema, projetada para melhorar a estabilidade da frequência e prover suporte inercial. Portanto,
o VSM realiza a conexão entre lado CC e CA da Microrrede, onde a energia disponível na rede CC
é usada para prestar serviços anciliares no lado CA da Microrrede. Os resultados da simulação
mostram a eficácia da inércia adaptativa proposta, sendo realizada uma comparação entre o
controle droop e outras técnicas de controle convencionais
Power System Stability With a High Penetration of Inverter-Based Resources
Inverter-based resources (IBRs) possess dynamics that are significantly different from those of synchronous-generator-based sources and as IBR penetrations grow the dynamics of power systems are changing. This article discusses the characteristics of the new dynamics and examines how they can be accommodated into the long-standing categorizations of power system stability in terms of angle, frequency, and voltage stability. It is argued that inverters are causing the frequency range over which angle, frequency, and voltage dynamics act to extend such that the previously partitioned categories are now coupled and further coupled to new electromagnetic modes. While grid-forming (GFM) inverters share many characteristics with generators, grid-following (GFL) inverters are different. This is explored in terms of similarities and differences in synchronization, inertia, and voltage control. The concept of duality is used to unify the synchronization principles of GFM and GFL inverters and, thus, established the generalized angle dynamics. This enables the analytical study of GFM-GFL interaction, which is particularly important to guide the placement of GFM apparatuses and is even more important if GFM inverters are allowed to fall back to the GFL mode during faults to avoid oversizing to support short-term overload. Both GFL and GFM inverters contribute to voltage strength but with marked differences, which implies new features of voltage stability. Several directions for further research are identified, including: 1) extensions of nonlinear stability analysis to accommodate new inverter behaviors with cross-coupled time frames; 2) establishment of spatial–temporal indices of system strength and stability margin to guide the provision of new stability services; and 3) data-driven approaches to combat increased system complexity and confidentiality of inverter models
MODELLING WIND FARM WITH FREQUENCY RESPONSE FOR POWER SYSTEM DYNAMIC STUDIES
This dissertation presents an analytical study on modelling wind farm with frequency response
for power system dynamic studies. Recent trends indicate that wind energy penetration in the
power system will keep on increasing. This study models a permanent magnet synchronous
generator fully rated converter based wind farm, since this is one of the state of art technologies
that services this growing demand. Due to the variability in the wind resource, a high demand
will be placed on the frequency stability of the power system. This necessitates the requirement
of providing both inertial and governor support by the wind farm to the power system. High
wind penetration will have a significant impact on the power system stability. These impacts
needs to be investigated by conducting power system dynamic studies.
The main challenge is in identifying an appropriate level of complexity of the models to
represent power system electro-mechanical dynamics, while keeping the models as simple as
possible, to reduce the computational requirements. Taking this into consideration, the main
contribution of the modelling work, is identifying a full order model and a reduced order model
of a wind farm with frequency response. The dissertation presents the dynamic models of the
main components of a wind turbine and shows how the component models are combined to
generate a full order and reduced order model.
The wind farm is interfaced to the utility grid by a back to back voltage source converter.
Therefore selection of robust control structures and identification of control parameters constitutes
an important study element. Both, generator converter controller and grid converter controller
is given special attention. Auxiliary control loop for implementing frequency response is
identified and integrated to the models.
The power system under study is the Kundur s two area network. One synchronous generator
is substituted by the wind farm and contributes to 25% of the system capacity. The dynamic
system study investigates aspects of both frequency and small signal response.
The full order and reduced order model dynamic response, for a variable wind speed sequence,
shows a high degree of correspondence, both with and without frequency control. Therefore
the results of this work indicate that a reduced order model is sufficient to model power
system electro-mechanical dynamics without significant loss in accuracy. The full order and reduced order model small signal response, for constant wind speed and
without frequency control shows a high degree of correspondence. However the full order and
reduced order model response shows deviation, when the wind farm is supported with frequency
control. Therefore the full order model provides a more accurate small signal response
for wind farms with frequency control. The studied network reveals a poorly damped inter area
mode. Substitution of a synchronous generator by the wind farm, increases the damping of this
mode, decreasing inter area oscillations and enhancing system small signal stability.
The simulations of an over frequency event, in a system with a wind farm supporting frequency
control, clearly shows superior frequency response, in comparison to a wind farm without
frequency control. The salient performance is reflected in rate of change of frequency, temporary
maximum frequency, steady state frequency and settling time of the frequency response
Model predictive emissions control of a diesel engine airpath: Design and experimental evaluation
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/163480/2/rnc5188.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/163480/1/rnc5188_am.pd
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