Dynamics and control of parabolic trough collector loops with direct steam generation

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 m 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. Keywords: Parabolic trough; Direct steam generation; Power plant; Feed water control; Modelica; Dynamic simulation