Centrifugal Compressor Surge, Modeling and Identification for Control

In this chapter a general introduction of centrifugal compression systems is presented. The unstable surge phenomenon in compressors is discussed, as well as possible means to avoid or suppress this instability. From an assessment of the current state of the art in control-oriented modeling and identification, the research objectives are formulated. 1.1 General introduction The general topic of this thesis is surge in centrifugal compression systems. In particular it deals with the modeling and identification for control of the surge phenomenon. Surge is an unstable operating mode of a compression system that occurs at low mass flows. Surge not only limits compressor performance and efficiency but it can also damage the compressor and auxiliaries due to the large thermal and mechanical loads involved. Furthermore, the vibrations associated with surge can result in unacceptable noise levels. A promising technique to cope with surge is the active suppression of aerodynamic flow instabilities. When successful, active surge control enlarges the operational envelope of the compressor towards lowermass flows. Thereby, surge control makes the compression system more versatile and it allows the machine to run at the most efficient operating points, which are usually located near the surge initiation point. Research efforts over the past decades have led to important advancements in the field of surge control. Progress has been made with the analysis, modeling, and suppression of surge and promising experimental results on laboratory setups were reported. However, a real breakthrough in the practical application of active surge control on industrial scale installations has not been achieved, yet. The current research originates from work by Willems (2000) and Meuleman (2002) within theCompressor Surge Control project at the Department of Mechanical Engineering, Technische Universiteit Eindhoven. The project provided valuable new insights in the