The Logic Behind The Magic."Gas Turbine Compressor 2"

Compressor Surge Detection and Avoidance

The surge condition occurs when the compressor does not have enough flow to produce sufficient head and the gas in the discharge line will flows back into the compressor. This cycle of flow is called surge.
An anti surge valve is designed for surge control by recycling the flow to the suction line of  compressor.
The  input to the anti surge control are flow differential pressure across the flow meter, compressor suction and discharge pressures (Ps, Pd), temperatures,  and the anti surge valve position feedback.

The surge detector monitors flow differential pressure pulses across the flow meter. Flow pulse may indicate a compressor surge event. When a flow pulse occurs, the ASC step changes the command to the Anti surge valve to 15% more open to increase the flow into the compressor to prevent any possible surge. If the ASC detects 5 pulses within 10 second the train is cooldown shutdown.

The surge avoidance fuction is based on the reduced head vs. reduced flow factor.

The surge margin takes input of pressure, temperature and flow to calculate compressor surge margin which is defined to be distance from the operating reduced flow factor to the reduced flow factor at the surge limit line as a percentage.  The ASC compares the operating flow factor to keep the compressor operating a safe distance away from surge.
The ASC will begin to open the Anti surge valve if the surge margin drop below 10%.
PI algorithm is used to close and open the valve. One set of gains is used to slowly close the anti surge valve and another set to quickly close the anti surge valve. If the surge margin drops below 10% the ASC override manual modes.