Serial Compressor Load Sharing with Stable Surge-Aware Control
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Solution Overview
Problem
Conventional load sharing algorithms for compressor systems with serial compressors and shared flow control mechanisms often result in unstable control, leading to inverted reactions between valves, loss of control, and driving control valves to their limits, especially when operating near surge conditions.
Innovation Solution
The implementation of a performance controller and a cascaded load sharing controller that operate on pressure and load sharing parameters respectively, ensuring consistent control reactions and preventing premature anti-surge valve activation, even when compressors are close to surge conditions, by using intermediate pressure as a process parameter and adjusting control outputs to maintain stable and efficient load sharing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional load sharing algorithms are used for serial compressors with shared flow control mechanisms, then load distribution among compressors is achieved, but control stability deteriorates leading to inverted valve reactions and loss of control
Solution Approach 1:
The control system is segmented into separate functional controllers: a flow controller that manages overall flow distribution and individual compressor controllers that manage each compressor's operation. This segmentation allows each controller to operate independently with its own control logic, preventing the inverted reactions that occur in conventional unified control systems.
Solution Approach 2:
The control architecture inverts the conventional approach by having the flow controller set reference values for compressor controllers rather than having compressor controllers directly compete for flow allocation. This inversion of control hierarchy eliminates the instability and inverted valve reactions characteristic of conventional load sharing algorithms.
2Productivity
If conventional control algorithms operate near surge conditions, then compressor capacity is maximized, but control reliability deteriorates due to premature anti-surge valve activation
Solution Approach 1:
Each compressor controller is equipped with its own surge detection and anti-surge control logic tailored to the specific operating characteristics of that compressor. This localized control quality allows each compressor to be managed according to its individual surge margins, preventing premature anti-surge valve activation while maintaining optimal capacity near surge conditions.
Solution Approach 2:
The control system implements continuous feedback monitoring of surge conditions for each compressor through the compressor controller. This feedback mechanism allows the system to detect approaching surge conditions and adjust control actions accordingly, maintaining reliable operation at high capacity without premature anti-surge valve activation.
Data Source
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AI summary
In some aspects, a compressor system includes a compressor train including two or more compressors connected in series and a control mechanism. The control mechanism is controlled by a performance controller. The performance controller is operable to identify a process variable of the performance controller; receive, on a recurrent basis from a load sharing controller, a setpoint for the process variable of the performance controller; and control the control mechanism based on the setpoint and the process variable of the performance controller. The setpoint is determined dynamically during operation of the two or more compressors by the load sharing controller based on a load sharing parameter associated with the two or more compressors.