Method and device performing model based anti-surge dead time compensation
Methods and devices for performing a model based anti-surge dead time compensation in systems including a compressor and an anti-surge loop are provided. A new position of an anti-surge valve on the anti-surge loop is determined by correcting for dead time a value of the anti-surge parameter calculated from field measurements, based on a predicted anti-surge parameter estimated using a deterministic model which has as variables the field measurements and a current position of the anti-surge valve.
1. A fluid transport system, comprising:
a compressor configured to compress a fluid passing therethrough;
an anti-surge loop configured to allow a part of the fluid, after being discharged from the compressor, to be recycled back into an inlet of the compressor;
an anti-surge valve connected to the anti-surge loop, and configured to modify the flow of part of the fluid recycled, the modification of the flow of the fluid recycled being based on a position of the anti-surge valve; and
an anti-surge valve controller connected to the anti-surge valve, and configured to:
receive field measurements related to an anti-surge parameter in the fluid transport system;
predict an anti-surge parameter value after a most recently transmitted position of the anti-surge valve; and
modify the most recently transmitted position of the anti-surge valve to compensate for a delay between when the anti-surge controller transmitted the most recent position and when an effect of the most recent position is reflected by the field measurements in the fluid transport system based on the predicted anti-surge parameter value.
2. The fluid transport system of claim 1 , wherein the anti-surge valve controller is configured to calculate the modified position of the anti-surge valve based on a difference between a margin, which is a safe value of the anti-surge parameter, and a corrected value of the anti-surge parameter, which corrected value is calculated based on the received field measurements and compensated for the delay by using a model of the fluid transport system defining the predicted values.
3. The fluid transport system of claim 2 , wherein the anti-surge valve controller is configured to calculate the corrected value using an uncorrected value of the anti-surge parameter calculated using the field measurements, and an estimated value of the anti-surge parameter using the field measurements and the most recent position of the anti-surge valve as variables input to the model.
4. The fluid transport system of claim 3 , wherein the anti-surge valve controller is configured to calculate the uncorrected value of the anti-surge parameter as proportional to a differential pressure measurement of a flow element located close to a suction of the compressor weighted by a ratio of a design suction pressure and a current value of the suction pressure, the differential pressure measurement and the current value of the suction pressure being included in the field measurements.
5. The fluid transport system of claim 3 , wherein the anti-surge valve controller is configured to calculate the corrected value of the anti-surge parameter by adding a difference between the estimated value of the anti-surge parameter and an earlier estimated value of the anti-surge parameter, to the uncorrected value of the anti-surge parameter.
6. The fluid transport system of claim 1 , wherein the anti-surge valve controller comprises a Padé filter as a delay circuit to provide the earlier estimated value of the anti-surge parameter.
7. The fluid transport system of claim 1 , wherein the anti-surge parameter is a function of a total fluid flow passing through the compressor, the total fluid flow being a sum of an input flow and a flow of the part of the fluid which is recycled.
8. The fluid transport system of claim 2 , wherein the anti-surge valve controller is configured to calculate the margin based on the corrected value of the anti-surge parameter.