Post-fault Configuration Research Articles

Multiple Fault Tolerant Control Strategy for Rotor Field Oriented Induction Motor Drive Fed From CHB Converter With Redundant Cells

The article proposes a postfault control strategy for a rotor field oriented induction motor (RFO-IM) drive fed by a cascaded H-bridge multilevel converter (CHB-MLC) with redundant cells in each phase. The objective of the control strategy is to maintain the torque and speed of the RFO-IM in postfault operation and to maximize the converter's power capability by adding a maximum number of power cells during postfault operation. Furthermore, maximum line voltage is utilized from the redundant cells without increasing the dc-link voltage of power cells, and the motor's operating point in the voltage plane is analyzed and determined for various loading conditions during prefault and postfault operation. In the postfault operation, a common mode voltage of fundamental frequency is also added depending on the motor's loading condition and postfault configuration to distribute power evenly among the remaining healthy cells. Theoretical and graphical analyses include the equation of the operating point in the voltage plane, traversal of the operating point from prefault to postfault operation, and selection of common mode voltage of fundamental frequency based on the fault configuration and the motor's loading. The simulation and experimental data are used to validate the proposed fault-tolerant control approach.

Fault-Type Discrimination in HVDC Transmission Lines Using Rate of Change of Local Currents

A simple and yet dependable technique for fault-type identification in HVDC transmission systems is presented in this paper. A set of indices is defined for pairs of rate of change of current measurements to identify the pole(s) involved in the fault to discriminate the ground faults from those involved with the dedicated metallic return conductor. The proposed fault discrimination method will identify the faulty pole within a 1-ms window, and therefore, it can be used to improve the sensitivity and reliability of DC fault protection. Furthermore, the knowledge—whether or not the dedicated return conductor is involved in the fault—is useful for determining the post-fault configuration of bipole grids. Considerable discrimination margins are observed during the rigorous evaluation of the technique for two-conductor and three-conductor HVDC systems under various fault scenarios, for both considerably long overhead transmission lines and cables. The indices can be computed using local current measurements made using low-bandwidth sensors. They are independent of the fault resistance, and therefore, settings can be found easily.

Implementación del Método SIME (Single Machine Equivalent) en DIgSILENT PowerFactory para calcular Márgenes de Estabilidad Transitoria

Este trabajo presenta una herramienta computacional, basada en el Método SIME (Single Machine Equivalent), la cual permite evaluar problemas de estabilidad transitoria en sistemas eléctricos de potencia. Mediante esta herramienta se obtienen márgenes de estabilidad que orientan la definición de acciones de control preventivo para mejorar la seguridad dinámica del sistema de potencia. El software es desarrollado utilizando lenguaje de programación DIgSILENT Programming Language (DPL) y enfoca su análisis en la determinación de índices de seguridad dinámica que permiten evaluar en el comportamiento del sistema de potencia en su configuración post-falla en términos del equivalente OMIB (One Machine Infinite Bus). La evolución de las magnitudes eléctricas (ángulo y velocidad del rotor, potencia mecánica y eléctrica) del OMIB es calculada a partir de la evolución en el tiempo de las magnitudes eléctricas de las máquinas del sistema de potencia y a partir del criterio de igualdad de áreas EAC, se calculan los márgenes de estabilidad transitoria del sistema de potencia. Los resultados obtenidos de la aplicación de la metodología en el sistema de prueba IEEE New England, permiten verificar las bondades del método para calcular márgenes de estabilidad transitoria.

Application of the Co-Evolutionary Algorithm with Memory at the Population Level for Optimisation of the Operation of Real Electric Power Distribution Networks

A solution of the optimisation problem of complex power electric networks post-fault configuration has been proposed. The analysed problem of search for optimal configurations of electric power distribution networks for changing loadings of network elements and for malfunction conditions is a multi-criteria optimisation problem. In this case the sought-after solution is the collection of Pareto-optimal solutions. Scientific methods belonging to the class of artificial intelligence methods (evolutionary algorithms and classifier system) have been used in the paper. Scientific work of the author is presented the co-evolutionary algorithm using memory at the level of organised populations in the form of five subpopulations, the composition of which is changed and organised according to classifying systems’ procedures. The process of creating a collection of classifiers describing the substitute network configuration was performed by the author supported by the theoretical genetic basics of self-teaching system. Cooperation of the evolutionary algorithm with the classifier system enables significant reduction of the classification time, reduces the iterative calculation process on average by 40 %. The calculations performed for the mapped real system of the medium voltage municipal distribution network have given satisfactory results, confirming the adequate direction of the research. The method presented in the article enables effective search of optimal configurations of distribution networks for various network loadings and also network malfunction conditions

Application of evolutionary algorithm in optimisation of medium-voltage distribution networks post-fault configuration

A method of finding optimum post-fault configuration of distribution networks based on evolutionary algorithm has been presented in the paper. The description of the proposed algorithm together with the calculation procedures prepared for the considered problem has been included. Exemplary calculations for a selected medium-voltage network system have been presented in the final part of the paper.

Application of Classifier System and Co-Evolutionary Algorithm in Optimization of Medium-Voltage Distribution Networks Post-Fault Configuration

The methodology of restoring power supply to consumers in case of a distribution grid failure is an important issue in literature on operation and reliability of electrical energy distribution grids. The article presents a concept of a new method which supports the operation of distribution grids operators in case of a failure using a classifier system working in tandem with a coevolutionary algorithm. The method presented in the article enables constructing scenarios for adjustments to medium voltage power distribution grids configuration (power system switchgear operation adjustments). The developed method is based on the theoretical rudiments of genetic-based machine learning systems. The method uses information on previous power distribution grid failures and enables using information from simulated grid failures. Decision variables, which take into account the reliability parameters of distribution grid elements among other things, have been described using the fuzzy set theory. The final part of the article describes sample calculations related to failures of a selected actual power distribution grid performed using the developed method. Ill. 5, bibl. 12, tabl. 1 (in English; abstracts in English and Lithuanian). http://dx.doi.org/10.5755/j01.eee.115.9.740

Optimization approach to dynamic restoration of distribution systems

The problem of fault restoration in distribution systems is a multi-objective dynamic combinatorial problem with topology constraints. The problem consists in finding both (1) an admissible post-fault configuration and (2) the sequence of switching operations to reach such configuration. Research on the problem solution has been focusing on the search for admissible post-fault configurations; the sequencing of switching operations is usually disregarded. However, the sequencing of switching operations determines the admissibility of the intermediate configurations and therefore the effectiveness of the overall restoration plan. In this paper, we propose to address the problem of fault restoration in distribution systems in a two phase approach. In the first phase a network optimization evolutionary approach is proposed to find the optimal post-fault configuration. In the second phase a dynamic programming approach is proposed to determine the optimal sequence of switching operations. The two phase approach is illustrated with an example from a real urban distribution network.