Controller and method for reducing standby time when controlling the number of chillers to be operated
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Solution Overview
Problem
Chiller systems face instability in operation number control due to rapid load changes, leading to potential light load stops, as existing control methods rely on fixed standby times that may not adapt quickly enough to changing chilled water temperatures, resulting in either light load stops or load imbalances.
Innovation Solution
A control device that adjusts the standby time based on chilled water temperature and its rate of change, setting it to zero when conditions indicate a risk of light load stop, allowing for immediate stage changes to prevent chillers from entering a low-load state, thereby ensuring stable operation number control and preventing light load stops.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a fixed standby time is used for operation number control, then the system stability is improved, but the response speed to rapid load changes deteriorates
Solution Approach 1:
The standby time is changed from a fixed value to a dynamic value that adjusts based on the rate of change of load. When the load changes rapidly, the standby time is reduced or eliminated, allowing immediate stage changes. When the load is stable, the normal standby time is maintained to ensure system stability. This dynamic adjustment resolves the contradiction between stability and response speed.
Solution Approach 2:
The standby time parameter is modified based on the load change rate. By monitoring the load variation and adjusting the standby time parameter accordingly, the system can adapt to different operating conditions. This parameter change allows the system to maintain stability under normal conditions while responding quickly to rapid load changes.
2Reliability
If the standby time is shortened to prevent light load stop, then the response speed is improved, but the operation number control stability deteriorates
Solution Approach 1:
The standby time parameter is dynamically adjusted based on the load change rate and chilled water temperature conditions. When conditions indicate a risk of light load stop (rapid load decrease), the standby time is reduced to zero, enabling immediate stage decrease. This parameter change allows the system to prevent light load stops while maintaining overall control stability through conditional adjustment rather than permanent change.
Solution Approach 2:
The standby time is made dynamic rather than fixed, allowing it to shorten or eliminate itself only when necessary to prevent light load stop. This dynamic behavior enables the system to maintain stability during normal operation while providing rapid response capability when reliability risks arise, thus resolving the contradiction between reliability and stability.
3Speed
If the standby time is eliminated for immediate stage changes, then the response speed is improved, but the risk of load imbalance increases
Solution Approach 1:
The standby time parameter is conditionally adjusted based on monitored system parameters (load change rate, chilled water temperature). By changing the parameter only when necessary to prevent light load stop, the system achieves fast stage changes without unnecessarily sacrificing load balance stability. The conditional parameter change ensures that immediate stage changes occur only when safe and necessary.
Solution Approach 2:
The system continuously monitors load change rate and chilled water temperature to determine whether to reduce or eliminate standby time. This feedback mechanism ensures that immediate stage changes are only executed when system conditions indicate it is safe to do so, preventing load imbalance while maintaining the ability for rapid response when needed.
Data Source
AI summary
A control device for a refrigerator system for cooling a load by using a plurality of refrigerators, said control device comprising a unit to control the number of operating units that changes the number of operating refrigerators according to the load rate, and a cold water temperature acquisition unit that acquires, via a temperature sensor, the temperature of cold water affected by the refrigerators. After a prescribed standby time from when the number of operating refrigerators was changed has elapsed, the unit to control the number of operating units changes the number of operating units and reduces the prescribed standby time when at least one of the cold-water temperature and the rate of change in the cold-water temperature satisfies a prescribed condition.