80 research outputs found
TOWARDS OPTIMAL OPERATION AND CONTROL OF EMERGING ELECTRIC DISTRIBUTION NETWORKS
The growing integration of power-electronics converters enabled components causes low inertia in the evolving electric distribution networks, which also suffer from uncertainties due to renewable energy sources, electric demands, and anomalies caused by physical or cyber attacks, etc. These issues are addressed in this dissertation. First, a virtual synchronous generator (VSG) solution is provided for solar photovoltaics (PVs) to address the issues of low inertia and system uncertainties. Furthermore, for a campus AC microgrid, coordinated control of the PV-VSG and a combined heat and power (CHP) unit is proposed and validated. Second, for islanded AC microgrids composed of SGs and PVs, an improved three-layer predictive hierarchical power management framework is presented to provide economic operation and cyber-physical security while reducing uncertainties. This scheme providessuperior frequency regulation capability and maintains low system operating costs. Third, a decentralized strategy for coordinating adaptive controls of PVs and battery energy storage systems (BESSs) in islanded DC nanogrids is presented. Finally, for transient stability evaluation (TSE) of emerging electric distribution networks dominated by EV supercharging stations, a data-driven region of attraction (ROA) estimation approach is presented. The proposed data-driven method is more computationally efficient than traditional model-based methods, and it also allows for real-time ROA estimation for emerging electric distribution networks with complex dynamics
Grid-Connected Renewable Energy Sources
The use of renewable energy sources (RESs) is a need of global society. This editorial, and its associated Special Issue “Grid-Connected Renewable Energy Sources”, offers a compilation of some of the recent advances in the analysis of current power systems that are composed after the high penetration of distributed generation (DG) with different RESs. The focus is on both new control configurations and on novel methodologies for the optimal placement and sizing of DG. The eleven accepted papers certainly provide a good contribution to control deployments and methodologies for the allocation and sizing of DG
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
Control and Stability of Residential Microgrid with Grid-Forming Prosumers
The rise of the prosumers (producers-consumers), residential customers equipped with behind-the-meter distributed energy resources (DER), such as battery storage and rooftop solar PV, offers an opportunity to use prosumer-owned DER innovatively. The thesis rests on the premise that prosumers equipped with grid-forming inverters can not only provide inertia to improve the frequency performance of the bulk grid but also support islanded operation of residential microgrids (low-voltage distribution feeder operated in an islanded mode), which can improve distribution grids’ resilience and reliability without purposely designing low-voltage (LV) distribution feeders as microgrids.
Today, grid-following control is predominantly used to control prosumer DER, by which the
prosumers behave as controlled current sources. These grid-following prosumers deliver active and
reactive power by staying synchronized with the existing grid. However, they cannot operate if
disconnected from the main grid due to the lack of voltage reference. This gives rise to the increasing
interest in the use of grid-forming power converters, by which the prosumers behave as voltage sources. Grid-forming converters regulate their output voltage according to the reference of their own and exhibit load sharing with other prosumers even in islanded operation. Making use of grid-forming
prosumers opens up opportunities to improve distribution grids’ resilience and enhance the genuine
inertia of highly renewable-penetrated power systems.
Firstly, electricity networks in many regional communities are prone to frequent power outages. Instead of purposely designing the community as a microgrid with dedicated grid-forming equipment, the LV feeder can be turned into a residential microgrid with multiple paralleled grid-forming prosumers. In this case, the LV feeder can operate in both grid-connected and islanded modes. Secondly, gridforming prosumers in the residential microgrid behave as voltage sources that respond naturally to the varying loads in the system. This is much like synchronous machines extracting kinetic energy from rotating masses. “Genuine” system inertia is thus enhanced, which is fundamentally different from the “emulated” inertia by fast frequency response (FFR) from grid-following converters.
Against this backdrop, this thesis mainly focuses on two aspects. The first is the small-signal stability
of such residential microgrids. In particular, the impact of the increasing number of grid-forming
prosumers is studied based on the linearised model. The impact of the various dynamic response of
primary sources is also investigated. The second is the control of the grid-forming prosumers aiming to provide sufficient inertia for the system. The control is focused on both the inverters and the DC-stage converters. Specifically, the thesis proposes an advanced controller for the DC-stage converters based on active disturbance rejection control (ADRC), which observes and rejects the “total disturbance” of the system, thereby enhancing the inertial response provided by prosumer DER. In addition, to make better use of the energy from prosumer-owned DER, an adaptive droop controller based on a piecewise power function is proposed, which ensures that residential ESS provide little power in the steady state while supplying sufficient power to cater for the demand variation during the transient state. Proposed strategies are verified by time-domain simulations
Nonlinear constrained and saturated control of power electronics and electromechanical systems
Power electronic converters are extensively adopted for the solution of timely issues, such
as power quality improvement in industrial plants, energy management in hybrid electrical
systems, and control of electrical generators for renewables. Beside nonlinearity, this systems
are typically characterized by hard constraints on the control inputs, and sometimes
the state variables. In this respect, control laws able to handle input saturation are crucial
to formally characterize the systems stability and performance properties. From a practical
viewpoint, a proper saturation management allows to extend the systems transient
and steady-state operating ranges, improving their reliability and availability.
The main topic of this thesis concern saturated control methodologies, based on modern
approaches, applied to power electronics and electromechanical systems. The pursued
objective is to provide formal results under any saturation scenario, overcoming the
drawbacks of the classic solution commonly applied to cope with saturation of power converters,
and enhancing performance. For this purpose two main approaches are exploited
and extended to deal with power electronic applications: modern anti-windup strategies,
providing formal results and systematic design rules for the anti-windup compensator, devoted
to handle control saturation, and “one step” saturated feedback design techniques,
relying on a suitable characterization of the saturation nonlinearity and less conservative
extensions of standard absolute stability theory results.
The first part of the thesis is devoted to present and develop a novel general anti-windup
scheme, which is then specifically applied to a class of power converters adopted for power
quality enhancement in industrial plants. In the second part a polytopic differential inclusion
representation of saturation nonlinearity is presented and extended to deal with a
class of multiple input power converters, used to manage hybrid electrical energy sources.
The third part regards adaptive observers design for robust estimation of the parameters
required for high performance control of power systems
Advanced Modeling and Research in Hybrid Microgrid Control and Optimization
This book presents the latest solutions in fuel cell (FC) and renewable energy implementation in mobile and stationary applications. The implementation of advanced energy management and optimization strategies are detailed for fuel cell and renewable microgrids, and for the multi-FC stack architecture of FC/electric vehicles to enhance the reliability of these systems and to reduce the costs related to energy production and maintenance. Cyber-security methods based on blockchain technology to increase the resilience of FC renewable hybrid microgrids are also presented. Therefore, this book is for all readers interested in these challenging directions of research
Optimal Control of Hybrid Systems and Renewable Energies
This book is a collection of papers covering various aspects of the optimal control of power and energy production from renewable resources (wind, PV, biomass, hydrogen, etc.). In particular, attention is focused both on the optimal control of new technologies and on their integration in buildings, microgrids, and energy markets. The examples presented in this book are among the most promising technologies for satisfying an increasing share of thermal and electrical demands with renewable sources: from solar cooling plants to offshore wind generation; hybrid plants, combining traditional and renewable sources, are also considered, as well as traditional and innovative storage systems. Innovative solutions for transportation systems are also explored for both railway infrastructures and advanced light rail vehicles. The optimization and control of new solutions for the power network are addressed in detail: specifically, special attention is paid to microgrids as new paradigms for distribution networks, but also in other applications (e.g., shipboards). Finally, optimization and simulation models within SCADA and energy management systems are considered. This book is intended for engineers, researchers, and practitioners that work in the field of energy, smart grid, renewable resources, and their optimization and control
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