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The influence of a voltage sag ride-through system on the energy production of a doublyfed induction generator (DFIG) wind turbine is investigated. Using simulations, a candidate ride-through system based on insulated gate bipolar transistor (IGBT) modules with high current rating and with the option of having antiparallel thyristors, which can quickly disconnect the stator of the DFIG from the grid, is developed.It has been found that, by increasing the current rating of the converter IGBTs, the losses of the converter can be reduced. However, if antiparallel thyristors have to be connected between the stator and the grid in order to achieve a fast disconnection of the stator circuit, the overall losses of the total system increase instead.

The relationship of anatomical deadspace to transpulmonary pressure was studied in eight subjects awake, breathing spontaneously without endotracheal intubation, and anaesthetized intubated and ventilated artificially. Anatomical deadspace was determined according to the equal area method (Fowler) using carbon dioxide as a tracer gas. Volume measurements were performed using a pneumotachograph. Transpulmonary pressure was measured using an oesophageal balloon and a catheter which was connected to the mouthpiece during spontaneous breathing and inserted into the endotracheal tube during artificial ventilation. Anatomical deadspace was approximately the same during artificial ventilation and spontaneous breathing, despite bypass of the upper airway during anaesthesia. Anatomical deadspace was related linearly to transpulmonary pressure. The regression lines indicated an airway compliance of 3.6 ml/cm H2O during spontaneous breathing and 7.4 ml/cm H2O during artificial ventilation. The alteration in airway compliance caused by artificial ventilation is ascribed to a reduction in bronchial muscle tone.