Comparison Method for Differentiation of IEC 61850 based Substation Configuration Files

The increased construction and reconstruction of smart substations has exposed a problem with version management of substation configuration description language (SCL) files due to frequent changes. This paper proposes a comparative approach for differentiation of smart substation SCL configuration files. A comparison model for SCL configuration files is built in this method, which is based on the SCL structure and abstract model defined by IEC 61850. The proposed approach adopts the algorithms of depth-first traversal, sorting, and cross comparison in order to rapidly identify differences of changed SCL configuration files. This approach can also be utilized to detect malicious tampering or illegal manipulation tailoring for SCL files. SCL comparison software is developed using the Qt platform to validate the feasibility and effectiveness of the proposed approach.

Residential electrical vehicle charging strategies: the good, the bad and the ugly

In recent years, a wide variety of centralised and decentralised algorithms have been proposed for residential charging of electric vehicles (EVs). In this paper, we present a mathematical framework which casts the EV charging scenarios addressed by these algorithms as optimisation problems having either temporal or instantaneous optimisation objectives with respect to the different actors in the power system. Using this framework and a realistic distribution network simulation testbed, we provide a comparative evaluation of a range of different residential EV charging strategies, highlighting in each case positive and negative characteristics.

Loss-of-Main Monitoring and Detection for Distributed Generations Using Dynamic Principal Component Analysis

In this paper, our previous work on Principal Component Analysis (PCA) based fault detection method is extended to the dynamic monitoring and detection of loss-of-main in power systems using wide-area synchrophasor measurements. In the previous work, a static PCA model was built and verified to be capable of detecting and extracting system faulty events; however the false alarm rate is high. To address this problem, this paper uses a well-known ‘time lag shift’ method to include dynamic behavior of the PCA model based on the synchronized measurements from Phasor Measurement Units (PMU), which is named as the Dynamic Principal Component Analysis (DPCA). Compared with the static PCA approach as well as the traditional passive mechanisms of loss-of-main detection, the proposed DPCA procedure describes how the synchrophasors are linearly
auto- and cross-correlated, based on conducting the singular value decomposition on the augmented time lagged synchrophasor matrix. Similar to the static PCA method, two statistics, namely T2 and Q with confidence limits are calculated to form intuitive charts for engineers or operators to monitor the loss-of-main situation in real time. The effectiveness of the proposed methodology is evaluated on the loss-of-main monitoring of a real system, where the historic data are recorded from PMUs installed in several locations in the UK/Ireland power system.

The significance of interconnector counter-trading in a security constrained electricity market

Throughout the European Union there is an increasing amount of wind generation being dispatched-down due to the binding of power system operating constraints from high levels of wind generation. This paper examines the impact a system non-synchronous penetration limit has on the dispatch-down of wind and quantifies the significance of interconnector counter-trading to the priority dispatching of wind power. A fully coupled economic dispatch and security constrained unit commitment model of the Single Electricity Market of the Republic of Ireland and Northern Ireland and the British Electricity Trading and Transmission Arrangement was used in this study. The key finding was interconnector counter-trading reduces the impact the system non-synchronous penetration limit has on the dispatch-down of wind. The capability to counter-trade on the interconnectors and an increase in system non-synchronous penetration limit from 50% to 55% reduces the dispatch-down of wind by 311 GW h and decreases total electricity payments to the consumer by €1.72/MW h. In terms of the European Union electricity market integration, the results show the importance of developing individual electricity markets that allow system operators to counter-trade on interconnectors to ensure the priority dispatch of the increasing levels of wind generation.

An efficient and robust case sorting for algorithm for transient stability assessment

An efficient and robust case sorting algorithm based on Extended Equal Area Criterion (EEAC) is proposed in this paper for power system transient stability assessment (TSA). The time-varying degree of an equivalent image system can be deduced by comparing the analysis results of Static EEAC (SEEAC) and Dynamic EEAC (DEEAC), the former of which neglects all time-varying factors while the latter partially considers the time-varying factors. Case sorting rules according to their transient stability severity are set combining the time-varying degree and fault messages. Then a case sorting algorithm is designed with the “OR” logic among multiple rules, based on which each case can be identified into one of the following five categories, namely stable, suspected stable, marginal, suspected unstable and unstable. The performance of this algorithm is verified by studying 1652 contingency cases from 9 real Chinese provincial power systems under various operating conditions. It is shown that desirable classification accuracy can be achieved for all the contingency cases at the cost of very little extra computational burden and only 9.81% of the whole cases need to carry out further detailed calculation in rigorous on-line TSA conditions.

Identification of Small Signal Oscillation Mode Parameters from Simulated and Actual PMU Ringdown Data

This paper presents the practical use of Prony Analysis to identify small signal oscillation mode parameters from simulated and actual phasor measurement unit (PMU) ringdown data. A well-known two-area four-machine power system was considered as a study case while the latest PMU ringdown data were collected from a double circuit 275 kV main interconnector on the Irish power system. The eigenvalue analysis and power spectral density were also conducted for the purpose of comparison. The capability of Prony Analysis to identify the mode parameters from three different types of simulated PMU ringdown data has been shown successfully. Furthermore, the results indicate that the Irish power system has dominant frequency modes at different frequencies. However, each mode has good system damping.

IEEE C37.118-2 Synchrophasor Communication Framework

Synchrophasors have become an important part of the modern power system and numerous applications have been developed covering wide-area monitoring, protection and control. Most applications demand continuous transmission of synchrophasor data across large geographical areas and require an efficient communication framework. IEEE C37.118-2 evolved as one of the most successful synchrophasor communication standards and is widely adopted. However, it lacks a predefined security mechanism and is highly vulnerable to cyber attacks. This paper analyzes different types of cyber attacks on IEEE C37.118-2 communication system and evaluates their possible impact on any developed synchrophasor application. Further, the paper also recommends an efficent security mechanism that can provide strong protection against cyber attacks. Although, IEEE C37.118-2 has been widely adopted, there is no clear understanding of the requirements and limitations. To this aim, the paper also presents detailed performance evaluation of IEEE C37.118-2 implementations which could help determine required resources and network characteristics before designing any synchrophasor application.

Real-Time Multiple Event Detection and Classification Using Moving Window PCA

This paper proposes a method for the detection and classification of multiple events in an electrical power system in real-time, namely; islanding, high frequency events (loss of load) and low frequency events (loss of generation). This method is based on principal component analysis of frequency measurements and employs a moving window approach to combat the time-varying nature of power systems, thereby increasing overall situational awareness of the power system. Numerical case studies using both real data, collected from the UK power system, and simulated case studies, constructed using DigSilent PowerFactory, for islanding events, as well as both loss of load and generation dip events, are used to demonstrate the reliability of the proposed method.

Flexible management of bandwidth and redundancy in fieldbuses

Os sistemas distribuídos embarcados (Distributed Embedded Systems – DES) têm sido usados ao longo dos últimos anos em muitos domínios de aplicação, da robótica, ao controlo de processos industriais passando pela aviónica e pelas aplicações veiculares, esperando-se que esta tendência continue nos próximos anos. A confiança no funcionamento é uma propriedade importante nestes domínios de aplicação, visto que os serviços têm de ser executados em tempo útil e de forma previsível, caso contrário, podem ocorrer danos económicos ou a vida de seres humanos poderá ser posta em causa. Na fase de projecto destes sistemas é impossível prever todos os cenários de falhas devido ao não determinismo do ambiente envolvente, sendo necessária a inclusão de mecanismos de tolerância a falhas. Adicionalmente, algumas destas aplicações requerem muita largura de banda, que também poderá ser usada para a evolução dos sistemas, adicionandolhes novas funcionalidades. A flexibilidade de um sistema é uma propriedade importante, pois permite a sua adaptação às condições e requisitos envolventes, contribuindo também para a simplicidade de manutenção e reparação. Adicionalmente, nos sistemas embarcados, a flexibilidade também é importante por potenciar uma melhor utilização dos, muitas vezes escassos, recursos existentes. Uma forma evidente de aumentar a largura de banda e a tolerância a falhas dos sistemas embarcados distribuídos é a replicação dos barramentos do sistema. Algumas soluções existentes, quer comerciais quer académicas, propõem a replicação dos barramentos para aumento da largura de banda ou para aumento da tolerância a falhas. No entanto e quase invariavelmente, o propósito é apenas um, sendo raras as soluções que disponibilizam uma maior largura de banda e um aumento da tolerância a falhas. Um destes raros exemplos é o FlexRay, com a limitação de apenas ser permitido o uso de dois barramentos. Esta tese apresentada e discute uma proposta para usar a replicação de barramentos de uma forma flexível com o objectivo duplo de aumentar a largura de banda e a tolerância a falhas. A flexibilidade dos protocolos propostos também permite a gestão dinâmica da topologia da rede, sendo o número de barramentos apenas limitado pelo hardware/software. As propostas desta tese foram validadas recorrendo ao barramento de campo CAN – Controller Area Network, escolhido devido à sua grande implantação no mercado. Mais especificamente, as soluções propostas foram implementadas e validadas usando um paradigma que combina flexibilidade com comunicações event-triggered e time-triggered: o FTT – Flexible Time- Triggered. No entanto, uma generalização para CAN nativo é também apresentada e discutida. A inclusão de mecanismos de replicação do barramento impõe a alteração dos antigos protocolos de replicação e substituição do nó mestre, bem como a definição de novos protocolos para esta finalidade. Este trabalho tira partido da arquitectura centralizada e da replicação do nó mestre para suportar de forma eficiente e flexível a replicação de barramentos. Em caso de ocorrência de uma falta num barramento (ou barramentos) que poderia provocar uma falha no sistema, os protocolos e componentes propostos nesta tese fazem com que o sistema reaja, mudando para um modo de funcionamento degradado. As mensagens que estavam a ser transmitidas nos barramentos onde ocorreu a falta são reencaminhadas para os outros barramentos. A replicação do nó mestre baseia-se numa estratégia líder-seguidores (leaderfollowers), onde o líder (leader) controla todo o sistema enquanto os seguidores (followers) servem como nós de reserva. Se um erro ocorrer no nó líder, um dos nós seguidores passará a controlar o sistema de uma forma transparente e mantendo as mesmas funcionalidades. As propostas desta tese foram também generalizadas para CAN nativo, tendo sido para tal propostos dois componentes adicionais. É, desta forma possível ter as mesmas capacidades de tolerância a falhas ao nível dos barramentos juntamente com a gestão dinâmica da topologia de rede. Todas as propostas desta tese foram implementadas e avaliadas. Uma implementação inicial, apenas com um barramento foi avaliada recorrendo a uma aplicação real, uma equipa de futebol robótico onde o protocolo FTT-CAN foi usado no controlo de movimento e da odometria. A avaliação do sistema com múltiplos barramentos foi feita numa plataforma de teste em laboratório. Para tal foi desenvolvido um sistema de injecção de faltas que permite impor faltas nos barramentos e nos nós mestre, e um sistema de medida de atrasos destinado a medir o tempo de resposta após a ocorrência de uma falta.

Wind resource mapping using landscape roughness and spatial interpolation methods

Energy saving, reduction of greenhouse gasses and increased use of renewables are key policies to achieve the European 2020 targets. In particular, distributed renewable energy sources, integrated with spatial planning, require novel methods to optimise supply and demand. In contrast with large scale wind turbines, small and medium wind turbines (SMWTs) have a less extensive impact on the use of space and the power system, nevertheless, a significant spatial footprint is still present and the need for good spatial planning is a necessity. To optimise the location of SMWTs, detailed knowledge of the spatial distribution of the average wind speed is essential, hence, in this article, wind measurements and roughness maps were used to create a reliable annual mean wind speed map of Flanders at 10 m above the Earth’s surface. Via roughness transformation, the surface wind speed measurements were converted into meso- and macroscale wind data. The data were further processed by using seven different spatial interpolation methods in order to develop regional wind resource maps. Based on statistical analysis, it was found that the transformation into mesoscale wind, in combination with Simple Kriging, was the most adequate method to create reliable maps for decision-making on optimal production sites for SMWTs in Flanders.

Modelling real solar cell using PSCAD/MATLAB

This paper presents the development of a solar photovoltaic (PV) model based on PSCAD/EMTDC - Power System Computer Aided Design – including a mathematical model study. An additional algorithm has been implemented in MATLAB software in order to calculate several parameters required by the PSCAD developed model. All the simulation study has been performed in PSCAD/MATLAB software simulation tool. A real data base concerning irradiance, cell temperature and PV power generation was used in order to support the evaluation of the implemented PV model.

Logic programming and fuzzy Monte Carlo for distribution network reconfiguration

This paper present a methodology to choose the distribution networks reconfiguration that presents the lower power losses. The proposed methodology is based on statistical failure and repair data of the distribution power system components and uses fuzzy-probabilistic modeling for system component outage parameters. The proposed hybrid method using fuzzy sets and Monte Carlo simulation based on the fuzzyprobabilistic models allows catching both randomness and fuzziness of component outage parameters. A logic programming algorithm is applied, once obtained the system states by Monte Carlo Simulation, to get all possible reconfigurations for each system state. To evaluate the line flows and bus voltages and to identify if there is any overloading, and/or voltage violation an AC load flow has been applied to select the feasible reconfiguration with lower power losses. To illustrate the application of the proposed methodology, the paper includes a case study that considers a 115 buses distribution network.

A data-mining based methodology for wind forecasting

In many countries the use of renewable energy is increasing due to the introduction of new energy and environmental policies. Thus, the focus on the efficient integration of renewable energy into electric power systems is becoming extremely important. Several European countries have already achieved high penetration of wind based electricity generation and are gradually evolving towards intensive use of this generation technology. The introduction of wind based generation in power systems poses new challenges for the power system operators. This is mainly due to the variability and uncertainty in weather conditions and, consequently, in the wind based generation. In order to deal with this uncertainty and to improve the power system efficiency, adequate wind forecasting tools must be used. This paper proposes a data-mining-based methodology for very short-term wind forecasting, which is suitable to deal with large real databases. The paper includes a case study based on a real database regarding the last three years of wind speed, and results for wind speed forecasting at 5 minutes intervals.

Ancillary service market simulation

Power systems operation in a liberalized environment requires that market players have access to adequate decision support tool, allowing them to consider all the business opportunities and take strategic decisions. Ancillary services represent a good negotiation opportunity that must be considered by market players. For this, decision support tools must include ancillary market simulation. This paper deals with ancillary services negotiation in electricity markets. The proposed concepts and methodologies are implemented in MASCEM, a multi-agent based electricity market simulator. A test case concerning the dispatch of ancillary services using two different methods (Linear Programming and Genetic Algorithm approaches) is included in the paper.

Reliability and availability in reconfigurable computing: a basis for a common solution

Dynamically reconfigurable SRAM-based field-programmable gate arrays (FPGAs) enable the implementation of reconfigurable computing systems where several applications may be run simultaneously, sharing the available resources according to their own immediate functional requirements. To exclude malfunctioning due to faulty elements, the reliability of all FPGA resources must be guaranteed. Since resource allocation takes place asynchronously, an online structural test scheme is the only way of ensuring reliable system operation. On the other hand, this test scheme should not disturb the operation of the circuit, otherwise availability would be compromised. System performance is also influenced by the efficiency of the management strategies that must be able to dynamically allocate enough resources when requested by each application. As those resources are allocated and later released, many small free resource blocks are created, which are left unused due to performance and routing restrictions. To avoid wasting logic resources, the FPGA logic space must be defragmented regularly. This paper presents a non-intrusive active replication procedure that supports the proposed test methodology and the implementation of defragmentation strategies, assuring both the availability of resources and their perfect working condition, without disturbing system operation.