6,053 research outputs found
Sparse Wide-Area Control of Power Systems using Data-driven Reinforcement Learning
In this paper we present an online wide-area oscillation damping control
(WAC) design for uncertain models of power systems using ideas from
reinforcement learning. We assume that the exact small-signal model of the
power system at the onset of a contingency is not known to the operator and use
the nominal model and online measurements of the generator states and control
inputs to rapidly converge to a state-feedback controller that minimizes a
given quadratic energy cost. However, unlike conventional linear quadratic
regulators (LQR), we intend our controller to be sparse, so its implementation
reduces the communication costs. We, therefore, employ the gradient support
pursuit (GraSP) optimization algorithm to impose sparsity constraints on the
control gain matrix during learning. The sparse controller is thereafter
implemented using distributed communication. Using the IEEE 39-bus power system
model with 1149 unknown parameters, it is demonstrated that the proposed
learning method provides reliable LQR performance while the controller matched
to the nominal model becomes unstable for severely uncertain systems.Comment: Submitted to IEEE ACC 2019. 8 pages, 4 figure
Um estudo sobre métodos de determinação de estados e parâmetros de máquinas síncronas de polos salientes
Orientador: Mateus GiesbrechtDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de ComputaçãoResumo: As máquinas síncronas de polos salientes desempenham um papel fundamental na análise de estabilidade de sistemas elétricos de potência, especialmente em países cuja maior parte da energia gerada provém de fontes hidráulicas. Os modelos elétricos equivalentes que descrevem o comportamento dessas máquinas são compostos por diversos parâmetros, os quais são utilizados em uma ampla gama de estudos. No presente trabalho, estudam-se e propõem-se técnicas de estimação de estados e parâmetros de máquinas síncronas de polos salientes. A princípio, as equações de tensão, de fluxos concatenados, de potência e de movimento são desenvolvidas com as devidas unidades de medida, tanto em variáveis de máquina quanto em variáveis projetadas sobre um plano ortogonal que gira na velocidade elétrica do rotor. Na maior parte da literatura, essas unidades não são explicitadas no equacionamento. Dentre os parâmetros elétricos dos modelos das máquinas síncronas de polos salientes, as reatâncias de magnetização são os que mais influenciam o comportamento da máquina em condições de regime permanente senoidal. Desta forma, apresenta-se uma nova abordagem à estimação do ângulo de carga dessas máquinas e o subsequente cálculo das reatâncias de magnetização a partir de condições de carga específicas -- o desempenho do método proposto é avaliado em dados de simulação e em dados reais de operação de um gerador síncrono de grande porte. Algumas abordagens à determinação de parâmetros requerem que a máquina seja posta fora de operação para que ensaios específicos possam ser realizados. Dentre eles, um dos mais empregados na determinação de parâmetros transitórios e de regime permanente é o ensaio de rejeição de carga; assim, este ensaio também é analisado e aperfeiçoado por um método automatizado de separação de soma de exponenciais baseado em projeção de variáveis. Por tratar-se de um sistema multivariável e altamente não linear, diferentes observadores de estado também são utilizados para se determinarem estados e parâmetros de máquinas síncronas em tempo hábil e com precisão satisfatória. Este trabalho apresenta uma abordagem não linear recursivamente aplicável à estimação de fluxos concatenados, correntes de enrolamentos amortecedores, ângulo de carga e reatâncias de magnetização de máquinas síncronas de polos salientes por meio da filtragem de partículas. Um modelo não linear de oitava ordem é considerado e apenas as medições realizadas nos terminais da armadura e do campo durante regime permanente se fazem necessárias para estimar as referidas grandezasAbstract: Salient-pole synchronous machines play a fundamental role in the stability analysis of electrical power systems, especially in countries where most of the generated energy comes from hydraulic sources. The electrical equivalent models that describe the behavior of these machines are composed of several electrical parameters, which are used in a wide range of studies. In the present work, techniques for estimating states and parameters of salient-pole synchronous machines are studied and proposed. A priori, the voltage, flux linkage, power, and motion equations are developed with the appropriate units included, both in machine variables and in variables projected on an orthogonal plane rotating in the rotor's electrical speed. In most of the literature, these units are not explained in the equation process. Among the electrical parameters, the magnetizing reactances are the ones that most influence the machine behavior under transient and steady-state conditions. In this way, a new approach to estimate the load angle of these machines and the subsequent calculation of the magnetizing reactances from specific load conditions are presented -- the performance of the proposed method is evaluated by means of simulation data and by operating data of a large synchronous generator. Some approaches to determine parameters require the machine to be taken out of operation, so that specific tests may be performed. Among them, one of the most used to determine transient and steady-state parameters is the load rejection test; thus, this test is also analyzed and refined by an automated method based on variable projection for separating the resulting sum-of-exponentials. Since the machines are highly nonlinear, multivariate, dynamic systems, different state observers seek to solve the state estimation problem in a timely manner and with satisfactory accuracy. This work presents a nonlinear and recursive approach for the estimation of flux linkages per second, amortisseur winding currents, load angle, and magnetizing reactances of salient-pole synchronous machines by means of the particle filtering. An eighth-order nonlinear model is considered, and only measurements taken at the machine terminals are necessary to estimate these quantitiesMestradoAutomaçãoMestre em Engenharia Elétrica162015/2018-6CNPq
Optimal PMU Placement for Power System Dynamic State Estimation by Using Empirical Observability Gramian
In this paper the empirical observability Gramian calculated around the
operating region of a power system is used to quantify the degree of
observability of the system states under specific phasor measurement unit (PMU)
placement. An optimal PMU placement method for power system dynamic state
estimation is further formulated as an optimization problem which maximizes the
determinant of the empirical observability Gramian and is efficiently solved by
the NOMAD solver, which implements the Mesh Adaptive Direct Search (MADS)
algorithm. The implementation, validation, and also the robustness to load
fluctuations and contingencies of the proposed method are carefully discussed.
The proposed method is tested on WSCC 3-machine 9-bus system and NPCC
48-machine 140-bus system by performing dynamic state estimation with
square-root unscented Kalman filter. The simulation results show that the
determined optimal PMU placements by the proposed method can guarantee good
observability of the system states, which further leads to smaller estimation
errors and larger number of convergent states for dynamic state estimation
compared with random PMU placements. Under optimal PMU placements an obvious
observability transition can be observed. The proposed method is also validated
to be very robust to both load fluctuations and contingencies.Comment: Accepted by IEEE Transactions on Power System
Quantum Cellular Automata
Quantum cellular automata (QCA) are reviewed, including early and more recent
proposals. QCA are a generalization of (classical) cellular automata (CA) and
in particular of reversible CA. The latter are reviewed shortly. An overview is
given over early attempts by various authors to define one-dimensional QCA.
These turned out to have serious shortcomings which are discussed as well.
Various proposals subsequently put forward by a number of authors for a general
definition of one- and higher-dimensional QCA are reviewed and their properties
such as universality and reversibility are discussed.Comment: 12 pages, 3 figures. To appear in the Springer Encyclopedia of
Complexity and Systems Scienc
Longitudinal Phase Space Tomography with Space Charge
Tomography is now a very broad topic with a wealth of algorithms for the reconstruction of both qualitative and quantitative images. In an extension in the domain of particle accelerators, one of the simplest algorithms has been modified to take into account the non-linearity of large-amplitude synchrotron motion. This permits the accurate reconstruction of longitudinal phase space density from one-dimensional bunch profile data. The method is a hybrid one which incorporates particle tracking. Hitherto, a very simple tracking algorithm has been employed because only a brief span of measured profile data is required to build a snapshot of phase space. This is one of the strengths of the method, as tracking for relatively few turns relaxes the precision to which input machine parameters need to be known. The recent addition of longitudinal space charge considerations as an optional refinement of the code is described. Simplicity suggested an approach based on the derivative of bunch shape with the properties of the vacuum chamber parametrized by a single value of distributed reactive impedance and by a geometrical coupling coefficient. This is sufficient to model the dominant collective effects in machines of low to moderate energy. In contrast to simulation codes, binning is not an issue since the profiles to be differentiated are measured ones. The program is written in Fortran 90 with High-Performance Fortran (HPF) extensions for parallel processing. A major effort has been made to identify and remove execution bottlenecks, for example by reducting floating-point calculations and recoding slow intrinsic functions. A pointer-like mechanism which avoids the problems associated with pointers and parallel processing has been implemented. This is required to handle the large, sparse matrices that the algorithm employs. Results obtained with and without the inclusion of space charge are presented and compared for proton beams in the CERN PS Booster. Comparisons of execution times on different platforms are presented and the chosen solution for our application program, which uses a dual processor PC for the number crunching, is described
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