Anti-surge control: Control theoretic analysis of existing anti-surge control strategies
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This report on compressor anti-surge control closes some of the gaps related to the significant properties of control strategies. Anti-surge control is an important issue in operation of e.g. oil and gas processing plants. However, control strategies have not previously been studied thoroughly from a control theoretic viewpoint. Special attention is given to the input-output relationship between recycle valve opening and control variable when changing the compressor speed. The properties are then validated through simulations.The compression system is found to be open-loop stable for operating points along the surge control line. However, the behaviour of control variable in different points is highly dependent on control strategy. A normalized control variable structure based on a operating point invariant to inlet conditions will perform similarly for a range of compressor speeds. The report also provide greater insight in the dynamics of the compression system, along with guidelines for strategy analysis and synthesis and controller tuning.