A GES mass flow observer for compression systems: Design and Experiments

Abstract

In this paper we present a novel globally exponentially stable (GES) mass flow observer for compression systems. A nonlinear separation principle for a class of controllers for the compression system is shown, allowing a control law and the proposed observer to be tuned separately. The results are supported by simulations and experiments. I. BACKGROUND Towards low mass flows, the stable operating region of centrifugal compressors is bounded due to the occurrence of surge. Surge is characterized by oscillations in the pressure rise and mass flow. These oscillation can cause severe damage to the machine due to vibrations and high thermal loading resulting from lowered efficiency. Surge is an unstable operation mode of the compressor and the stability boundary in the compressor map is called the surge line. Traditionally, surge has been avoided using surge avoidance schemes. Such schemes use various measurements in order to keep the operating point of the compressor away from the region where surge occurs. Typically, a surge control line is drawn at a distance away from the surge line, and the surge avoidance scheme ensures that the operating point does not cross this line. This method restricts the operating range of the machine, and efficiency is limited. Usually a recycle line around the compressor is used as actuation. Active surge control is fundamentally different from surge avoidance. In an active surge control scheme the open loop unstable phenomena is sought stabilized rather than avoided. Thus the operating regime of the machine is enlarged. Active surge control of compressors was first introduced by [1], and since then a number of results have been published. Different actuators have been used and examples include recycle, bleed and throttle valves, gas injection, variable guide vanes, drive torque and a number of others. For an overview, consult [2] and [3]. Several active surge control algorithms rely on feedback from mass flow. It is however well known that real time measurements of mass flow is both expensive and hampered with high noise levels. This motivates the work of designing surge controllers using mass flow observers, where the mass flow estimate is used in the control algorithms rather than mass flow measurement. In [4] a mass flow observer was proposed, and a separation principle allowing the controller and the observer to be tuned separately was shown. The observer algorithm from [4] uses a model for the compressor characteristics. The p01 p01 Compressor Duct Plenum Throttle

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Cite this paper

@inproceedings{Bhagen2004AGM, title={A GES mass flow observer for compression systems: Design and Experiments}, author={Bj\ornar B\ohagen and Olav Stene and Jan Tommy Gravdahl}, year={2004} }