219 research outputs found
OPTIMAL POWER FLOW CONTROL OF NETWORKED DC MICROGRIDS
The US military is moving toward the electrification of many weapon systems and platforms. Advanced weapon systems such as high energy radar, electro-magnetic kinetic weapons and directed energy pose significant integration challenges due to their pulsed power electrical load profile. Additionally, the weapons platforms, including ships, aircraft, and vehicles can be studied as a mobile microgrids with multiple generation sources, loads, and energy storage. There is also a desire to extend the mission profile and capabilities of these systems. Common goals are to increase fuel efficiency, maintaining system stability, and reduce energy storage size as typically required to enable pulsed load devices. To achieve these goals, there is an opportunity to optimize system performance by considering system wide exergy, a measure of the useful energy within the system. By studying exergy, systems with multi-physical coupling, as with electrically pulsed devices that require cooling, the system can be optimized holistically. While numerous optimization approaches exist, many focus on the long term, hours to days, energy management problem. Furthermore, advance control strategies such as the Hamiltonian Surface Shaping Power Flow Controller (HSSPFC) require feedforward operating points about which storage is actuated to maintain stability. Storage size can be reduced by combining the HSSPFC with exergy based optimization strategies designed for sub-second update rates. In this dissertation, several numerical and closed form/numerical hybrid optimization strategies were developed where speed of solution was explored vs. microgrid asset size, in non-realtime simulation. Then an exergy based optimization strategy was combined with the HSSPFC on a three bus networked microgrid model using average switch mode models, pulse loading, and a thermal system. The three bus model was then extended to a co-simulation on Hardware-in-the-loop (HIL) using an Opal- RT OP5700 and Typhoon HIL 600 realtime simulators, where the optimization was executed asynchronously through UDP Ethernet communication. The storage utilization was reduced by orders of magnitude when comparing two cases of optimized vs. non-optimized generation settings. Bus voltage regulation was within 5 % where there was a trade off between optimization update rate, transient regulation, and storage utilization. Contributions of this work are summarized as follows. An exergy based, asynchronous, optimization strategy was developed to work in concert with the HSSPFC strategy where sub-second update rates were achieved. A co-simulation test bench was developed to allow the study of advanced control strategies through the use of multiple realtime HIL simulators. The methodology for integrating the HIL simulators is given including wiring, calibration, signal scaling, and implementation specific details. An on-line optimization strategy was also developed to interact with the HIL system and used for determining power converter duty cycle biases
Stabilization of DC–DC buck converter with unknown constant power load via passivity-based control plus proportion-integration
Abstract It is known that constant power load (CPL) may cause a negative impedance, which seriously affects the stability of power system. In this paper, a new control algorithm for DC–DC buck converter feeding unknown CPL is proposed. First, under the assumption of known extracted power load, the standard passivity–based control (PBC) is presented to reshape the system energy and compensate for the negative impedance and a proportion‐integration (PI) action around passive output is added to improve disturbance rejection performance, which forms the PBC plus PI (PBC+PI). Then, a parameter estimation algorithm is developed, based on immersion and invariance (I&I) technique, in order to online estimate the extracted power load. In the next step, the online estimation scheme is adopted to construct an adaptive strategy. Finally, the stability analysis of the cascaded system containing a closed‐loop control system and observer error dynamics is conducted. Simulation and experimental results are demonstrated to validate the performance of the proposed controller
PID passivity-based droop control of power converters:Large-signal stability, robustness and performance
We present a full review of PID passivity-based controllers (PBC) applied to power electronic converters, discussing limitations, unprecedented merits and potential improvements in terms of large-signal stability, robustness and performance. We provide four main contributions. The nominal case is first considered and it is shown—under the assumption of perfect knowledge of the system parameters—that the PID-PBC is able to guarantee global exponential stability of a desired operating point for any positive gains. Second, we analyze robustness of the controller to parameters uncertainty for a specific class of power converters, by establishing precise stability margins. Third, we propose a modification of the controller by introducing a leakage, in order to overcome some of the intrinsic performance and robustness limitations. Interestingly, such controller can be interpreted at steady-state as a droop between the input and the passive output, similar to traditional primary controllers. Fourth, we robustify the design against saturation of the control input via an appropriate monotone transformation of the controller. The obtained results are thoroughly discussed and validated by simulations on two relevant power applications: a DC/DC boost converter and an HVDC grid-connected voltage source converter
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
- …