Centrifugal Compressor Shutdown Control to Prevent Backflow and Surge
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Solution Overview
Problem
Existing refrigeration systems with centrifugal compressors face challenges during shutdown, including refrigerant backflow, compressor reversal, noise, and surge, which can damage the compressor and reduce system reliability.
Innovation Solution
A method for controlling the shutdown of a centrifugal compressor involves grading the inlet opening and adjusting the rotation speed in a preset order. When the inlet opening is below a certain value, the drive motor is shut down. For larger inlet openings, the inlet opening is decreased and the rotation speed is increased, avoiding backflow and surge.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the drive motor is shut down directly when the inlet opening is large, then the shutdown process is simple and fast, but refrigerant backflow occurs causing compressor reversal and bearing damage
Solution Approach 1:
The shutdown process is segmented into multiple stages based on inlet opening thresholds. When inlet opening exceeds the first threshold, the system executes a multi-step shutdown sequence: closing inlet guide vanes, shutting down the drive motor, and maintaining rotor rotation for a predetermined time before complete shutdown. This segmentation prevents refrigerant backflow by controlling the sequence of operations, thereby protecting the compressor while managing complexity through structured control logic.
Solution Approach 2:
The system performs preliminary actions before complete shutdown by maintaining rotor rotation for a predetermined time after the drive motor is shut down. This preliminary action allows the rotor to continue rotating and preventing refrigerant backflow and compressor reversal, thereby protecting the compressor bearings and internal components from damage during the transition to complete shutdown.
2Reliability
If the inlet guide vanes are closed quickly to prevent backflow, then compressor protection is improved, but surge occurs due to rapid pressure changes
Solution Approach 1:
The system employs periodic or staged action by closing inlet guide vanes in a controlled sequence rather than immediately. When inlet opening exceeds the first threshold, the system closes the inlet guide vanes and shuts down the drive motor, then maintains rotor rotation for a predetermined time. This staged approach allows pressure to equalize gradually, preventing surge phenomenon while still protecting the compressor from refrigerant backflow damage.
3Loss of energy
If the compressor shuts down without maintaining rotor rotation, then energy consumption is reduced, but refrigerant backflow causes noise and bearing impingement
Solution Approach 1:
The system performs preliminary action by maintaining rotor rotation for a predetermined time after the drive motor is shut down. During this transition period, the rotor continues rotating which prevents refrigerant backflow, compressor reversal, and bearing impingement. Only after this predetermined time elapses and the rotor has sufficiently slowed does the system complete the shutdown, minimizing energy consumption while protecting against harmful effects.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method ensures a smooth and reliable shutdown of the centrifugal compressor, reducing backflow, noise, and the risk of surge, thereby enhancing the system's reliability, lifespan, and user experience.
Implementation Method 1
the drive motor of the centrifugal compressor is turned off... the absence of the large pressure difference provided by the centrifugal compressor
Implementation Method 2
decreasing the inlet opening of the centrifugal compressor... adjusting inlet guide vanes of the centrifugal compressor
Data Source
Figure 1
AI summary
A control method for a centrifugal compressor and an air conditioning system are provided. The control method for the centrifugal compressor comprises: S100, when an inlet opening of the centrifugal compressor is below a first preset value, shutting down a drive motor of the centrifugal compressor; or S200, when the inlet opening of the centrifugal compressor is not below the first preset value, performing the following operations in a preset order: decreasing the inlet opening of the centrifugal compressor, and increasing a rotation speed of the centrifugal compressor. According to solutions of the present invention, the control method of the centrifugal compressor provides higher reliability, longer lifetime, and lower noise for the air conditioning system to which it is applied