Abstract
Electrical utilities are confronted daily with unpredictable events in their grids, which may lead to severe security level repercussions in the system, far exceeding all the security principles used for operation and consequently jeopardizing the essential service to the consumers. Incidents are unpredictable disturbances and recent experiences prove that severe contingencies happen. Given these facts, the need to evaluate harsher contingencies arose and such analysis must be rigorous and exhaustive. The security principles used for planning and system operation determine that, given an incident in the Electrical Power System (EPS) which involves the breakdown of any grid element or the simultaneous failure of a double circuit overhead line or the failure of the largest generator in service the supply interruption shall never take place (excluding single-feeding points without alternative) or permanent overloads. To analyse the steady-state security of an EPS it is required too, accurately and efficiently identify the critical contingencies set, i.e., those that when occur may endanger the system's security. The steady-state simulations of the Portuguese Transmission System (PTS) were made in PSS/E software from Siemens PTI using snapshots that represent pictures of the real system. All these security studies produce a large amount of data and information. Recently, the Rough Sets Theory (RST) has been used successfully to handle efficiently problems where large amounts of data are produced. RST constitute a framework for inducing minimal decision rules. These rules in turn can be used to perform a classification task. The main goal of the rough set analysis is to search large databases for meaningful decision rules and finally acquire new knowledge. This approach is based on four main topics: Indiscernibility, Approximation, Reducts and Decision rules. A reduct is a minimal set of attributes from the whole attributes set that preserves the partitioning of the finite set of objects and therefore the original classes. It means that if the redundant attributes are eliminated the reducts are found. Decision rules extracted knowledge, can be used when classifying new objects not in the original information system. In this paper it is proposed an efficient study and contingency analysis in the PTS using the RST. The developed methodology produces a system operation classification, distinguishing in four possible states: normal, alert, emergency I and emergency II. These different operating states correspond to a four levels of security. The four states can be classified horizontally as secure, in normal state and insecure for the remaining ones. The computer programs SecurMining2.0 developed, were applied to the Portuguese test power network.

Abstract
In this paper it is presented a methodology to assess the dynamic voltage stability of an electric power system using trajectory sensitivity analysis. Trajectory sensitivity analysis can provide valuable insights into the security of an electric power system. In this study it was simulated a significant disturbance in two test power network. The Automatic Voltage Regulator of the generating units, the Under Load Tap Changer and loads models were taken into account. The simulation results were obtained using EUROSTAG program and post-processing module developed using the Matlab software package. © 2011 INESC Coimbra.

Abstract
State estimator is vital for on-line power system monitoring, analysis and control. With the increasing use of synchronized phasor measurement units (PMU) in power grids, how to utilize phasor measurements to improve the precision of state estimator becomes imperative. In this paper, a state estimator including voltage phasors, injected current phasors and traditional measurements is proposed. 14 IEEE bus system and 30 IEEE bus system are used as test systems and the simulation results demonstrate that the presented state estimation algorithm combining traditional SCADA measurements with PMU (Phasor Measurement Unit) measurements for power system state estimation improves the precision greatly. © 2011 INESC Coimbra.

Abstract

Abstract
In this article, we propose a linear parameterization (LP) for representing the friction in the tire-road interface, suitable for on-line Identification. This model was obtained by employing function approximation techniques, which results in an optimization problem to minimize the fitting error between the LP and the nonlinear Burckhardt model. Compared with others LPs proposed in the literature, the optimal LP features a reduced number of parameters and good approximation capabilities. Moreover, the proposed model can be identified though linear Identification techniques, simplifying the on-line peak friction estimation. Simulation results obtained with a vehicle simulator demonstrates the effectiveness of the proposed parameterization. © 2011 IFAC.

Abstract
In this paper, a detailed description of a control architecture for managing the DC link control of EVs with multiple energy sources is presented. The proposed topology allows the control of the power flow among supercapacitors and batteries, while ensuring the regulation of the DC link voltage, thanks to a cascade of voltage and current linear controllers. A simple analytical study is provided to illustrate the tuning guidelines for the current and voltage, based on proportional + integral controllers. A prototype system has been designed and built in reduced scale hardware to analyze the performance of the proposed control system. The experimental results are in accordance with the simulations and demonstrated the effectiveness of the proposed control technique. © 2011 IEEE.