Parabolic trough power plants with direct steam generation technology are a promising option for the production of electricity from renewable energy resources. For the layout of the collector field and the design of the control system the knowledge of the short-time dynamics is of essential importance. To study the dynamic behaviour a transient non-linear simulation tool is developed based on the Modelica language. The impact of over-all and local shadings of an 1000 in collector loop is simulated. Different feed water control systems are developed, implemented and evaluated. It turns out that in addition to the liquid level control of the buffer tank a fast feedback of the actual steam production is necessary for a good performance. For the case of steam temperature control by an injection cooler, it is shown that feedforward control significantly reduces the temperature deviations compared to a simple proportional-integral controller. The reaction of the controlled loop is simulated under a varity of irradiation disturbances. A key finding is that the orientation of the collector field relative to the moving clouds has large impact on the peak values during transients. (c) 2006 Elsevier Ltd. All rights reserved.