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Lisbon, Portugal

Marques G.D.,TULisbon | Sousa D.M.,TULisbon
IEEE Transactions on Energy Conversion | Year: 2012

The doubly fed induction generator (DFIG) is normally controlled with stator-flux orientation. The DFIG is a poorly damped system with a natural frequency near the grid frequency. This leads to natural oscillations on the stator flux and on other variables. When voltage dips occur, there are oscillations on the stator flux that produces electromotive forces and consequently disturbances on the rotor currents. This paper presents a comprehensive study of the DFIG during voltage dips. The method presented in this paper, valid for symmetric and for asymmetric voltage dips, is based on the classical model of the induction machine with stator flux orientation and neglects only a small part of the cross-coupling terms. The response depends on the design methodology of the proportional-integral inner controllers. Analytical, simulation, and experimental results are shown. The analysis and results can be divided into two sets depending if the voltage dip magnitude is smaller or deeper than 0.5 p.u. © 2012 IEEE. Source

Pires P.,TULisbon | Teodoro P.,TULisbon | Martins J.,TULisbon | da Costa J.S.,TULisbon
International Journal of Online Engineering | Year: 2012

The development of new robotic surgical instruments has brought significant improvements to the execution and outcome of surgical procedures. They allow shorter intraoperative interventions with higher precision of the surgical gesture, which has clear benefits for the patients, surgeons and hospitals. Perhaps the main retardant of the widespread of these new tools is the ability of getting the surgeon's hands-on with the new systems, for both initial evaluation and later on to overcome the initial learning curve. To accelerate this stage, and keep costs to a minimum, simulation tools have been introduced which allow physical surgeon-patient interaction through haptic devices. In this work, we focus on the Hip Resurfacing Surgical Procedure, and develop an interactive virtual environment for the insertion of the hip resurfacing guide wire with high precision and accuracy. The surgical tool used is a robotic arm that allows geometric accuracy and repeatability while the surgeon keeps control over the force exerted on the patient. Source

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