Time-domain harmonic state estimation of nonlinear load power systems with under-determined condition based on the extended Kalman filter

This contribution presents a time-domain methodology for harmonic state estimation of power systems with nonlinear loads based on the extended Kalman filter (EKF). The output variables measurements to be used in the state estimation algorithm are selected from the simulation of the propagated harmonics in the system with an under-determined condition of the measurement matrix. The state estimation results are compared against the actual time-domain system response; both results closely agree hence verifying the effectiveness of the EKF to solve the time-domain power system state estimation. Several sampling frequencies and measurement noise are applied to assess the effects on the state estimation process, the error covariance matrix, residuals and on the execution tim

Enhanced harmonic state estimation in unbalanced three-phase electrical grids based on the Kalman filter and physical scale-down implementation

A time-domain methodology is proposed based on Kalman filter, to determine the harmonic state estimation in three-phase electrical grids. Time-domain methodologies based on the Kalman filter need an initial solution to begin estimating the harmonic state in electrical grids. Previous methods have found this solution using simulated electrical grids; thus, the measurements taken from the simulations are synchronised only with the simulated grid model. In practical power networks, measurements taken from the grid need to be synchronised with the theoretical grid model. Synchronization between the model and measurements using the Kalman filter is proposed. This paper also proposes an alternative method to obtain the periodic steady-state solution in power grids. The method adequately processes the information given by a limited number of measurements to find the required solution. An experimental case study for a three-phase unbalanced condition with a nonlinear load and a limited number of measurements is used to validate the proposed methodology, i.e. practical data has been used instead of synthetic data. Hence, the results are validated by direct comparison of the state estimation response against the actual data recorded from the experimental laboratory implementation. The results show that using the proposed methodology, the time-domain harmonic state estimation can be efficiently applied to the analysis of practical power grids

Time domain harmonic state estimation in unbalanced power networks based on optimal number of meters and the principle of half-wave symmetry

This study proposes a time domain methodology for harmonic state estimation (HSE) in power systems. The proposed methodology is formulated to analyse the unbalanced operation of three-phase power systems including non-linear loads. It takes into account the optimal number of measuring devices and exploits the property of half-wave symmetry in voltage and current waveforms to significantly reduce the computational effort of the solution process. The results obtained are in close agreement with the actual response obtained from the time domain power system simulation performed with the SimPowerSystems toolbox of Simulink®. Hence, the proposed methodology can adequately assess the harmonic state in unbalanced power systems. The results show a considerable reduction in the instrumentation resources and time processing needed for HSE in non-linear power networks

Modelado y Análisis de Parques Eólicos: Referencia a Fenómenos Adversos en Calidad de la Energía.

En esta tesis se desarrollan e implementan modelos en espacio de estado para un aerogenerador y un parque eólico, su validación se realiza mediante el simulador digital Pscad/EMTDC. Estos modelos se aplican para analizar fenómenos adversos de la calidad de la energía debidos a la generación eólica. El aerogenerador y sus partes principales se describen, analizando la turbina eólica, el acoplamiento mecánico, el generador eléctrico, los controles, la conexión eléctrica a la red; se mencionan los tipos de aerogeneradores de acuerdo a su velocidad y control de potencia comprendiendo las diferentes formas de conexión a la red considerando las características de las turbinas eólicas y los generadores; con lo anterior se definen posibles topologías para la formación de parques eólicos y su conexión al sistema de potencia. La formulación del modelo para un aerogenerador en espacio de estado se analiza e implementa, la máquina de inducción se modela en coordenadas dq0 y marco de referencia síncrono, se describe el modelado del acoplamiento mecánico mediante una o varias masas. Se incorpora al modelo del aerogenerador en espacio de estado el control de ángulo de paso en las aspas de la turbina eólica para regular la potencia generada. También se describe el esquema de conexión de los aerogeneradores y parques eólicos a la red eléctrica de acuerdo al modelado matemático. Se presentan casos de estudio de un aerogenerador y un parque eólico para validar los modelos implementados en Matlab por comparación con los resultados de las simulaciones en Pscad/EMTDC. La influencia de la generación eólica sobre la calidad de la energía es descrita en fenómenos tales como depresiones de voltaje, parpadeo, armónicas y transitorios. Se realizan casos de estudio de una depresión de voltaje en el arranque de un aerogenerador, la generación de parpadeo (flicker) en la operación continua de los aerogeneradores, la emisión de armónicas debidas al efecto sombra de la torre del aerogenerador y un transitorio en la potencia generada de un parque eólico debido a un cambio en la potencia de referencia; los modelos implementados en espacio de estado en Matlab se utilizan en estos casos de estudio. Finalmente se obtienen conclusiones utilizando los casos de estudio realizados y se sugieren direcciones para continuar la investigación en esta área. Palabras clave: aerogenerador, armónicas, calidad de la energía, control, depresión de voltaje, espacio de estado, generación eólica, marco de referencia, máquina de inducción, modelado, parpadeo, parque eólico, ecuaciones diferenciales, transformada dq0, transitorios, variables de estado

Time-Domain Voltage Sag State Estimation Based on the Unscented Kalman Filter for Power Systems with Nonlinear Components

This paper proposes a time-domain methodology based on the unscented Kalman filter to estimate voltage sags and their characteristics, such as magnitude and duration in power systems represented by nonlinear models. Partial and noisy measurements from the electrical network with nonlinear loads, used as data, are assumed. The characteristics of voltage sags can be calculated in a discrete form with the unscented Kalman filter to estimate all the busbar voltages; being possible to determine the rms voltage magnitude and the voltage sag starting and ending time, respectively. Voltage sag state estimation results can be used to obtain the power quality indices for monitored and unmonitored busbars in the power grid and to design adequate mitigating techniques. The proposed methodology is successfully validated against the results obtained with the time-domain system simulation for the power system with nonlinear components, being the normalized root mean square error less than 3%

Periodic Steady State Assessment of Microgrids with Photovoltaic Generation Using Limit Cycle Extrapolation and Cubic Splines

This paper proposes a fast and accurate time domain (TD) methodology for the assessment of the dynamic and periodic steady state operation of microgrids with photovoltaic (PV) energy sources. The proposed methodology uses the trapezoidal rule (TR) technique to integrate the set of first-order differential algebraic equations (DAE), generated by the entire electrical system. The Numerical Differentiation (ND) method is used to significantly speed-up the process of convergence of the state variables to the limit cycle with the fewest number of possible time steps per cycle. After that, the cubic spline interpolation (CSI) algorithm is used to reconstruct the steady state waveform obtained from the ND method and to increase the efficiency of the conventional TR method. This curve-fitting algorithm is used only once at the end part of the algorithm. The ND-CSI can be used to assess stability, power quality, dynamic and periodic steady state operation, fault and transient conditions, among other issues, of microgrids with PV sources. The results are successfully validated through direct comparison against those obtained with the PSCAD/EMTDC simulator, widely accepted by the power industry

Altered Plasma Acylcarnitines and Amino Acids Profile in Spinocerebellar Ataxia Type 7

Spinocerebellar ataxia type 7 (SCA7), a neurodegenerative disease characterized by cerebellar ataxia and retinal degeneration, is caused by an abnormal CAG repeat expansion in the ATXN7 gene coding region. The onset and severity of SCA7 are highly variable between patients, thus identification of sensitive biomarkers that accurately diagnose the disease and monitoring its progression are needed. With the aim of identified SCA7-specific metabolites with clinical relevance, we report for the first time, to the best of our knowledge, a metabolomics profiling of circulating acylcarnitines and amino acids in SCA7 patients. We identified 21 metabolites with altered levels in SCA7 patients and determined two different sets of metabolites with diagnostic power. The first signature of metabolites (Valine, Leucine, and Tyrosine) has the ability to discriminate between SCA7 patients and healthy controls, while the second one (Methionine, 3-hydroxytetradecanoyl-carnitine, and 3-hydroxyoctadecanoyl-carnitine) possess the capability to differentiate between early-onset and adult-onset patients, as shown by the multivariate model and ROC analyses. Furthermore, enrichment analyses of metabolic pathways suggest alterations in mitochondrial function, energy metabolism, and fatty acid beta-oxidation in SCA7 patients. In summary, circulating SCA7-specific metabolites identified in this study could serve as effective predictors of SCA7 progression in the clinics, as they are sampled in accessible biofluid and assessed by a relatively simple biochemical assay