Methods and systems for detecting and recovering from control instability caused by impeller stall
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Solution Overview
Problem
Centrifugal chiller systems experience control instability and efficiency issues due to impeller stall, which conventional surge protection strategies, such as monitoring motor current fluctuations, are ineffective in detecting, leading to reduced reliability and customer dissatisfaction.
Innovation Solution
An impeller stall detection and recovery component within the chiller control unit calculates a control error signal frequency spectrum, determines high-frequency signal content, and adjusts the surge boundary control curve downward to restore stability, using a variable speed drive to manage compressor speed and inlet guide vane position.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional surge protection strategies (monitoring motor current fluctuations) are used, then the system structure remains simple, but impeller stall cannot be detected effectively
Solution Approach 1:
The patent replaces conventional mechanical/electrical monitoring methods (motor current fluctuation monitoring) with a signal processing approach based on control error signal frequency spectrum analysis. This substitution enables impeller stall detection through mathematical transformation of existing control signals rather than additional mechanical sensors, resolving the contradiction between detection capability and system complexity.
Solution Approach 2:
The patent introduces the control error signal frequency spectrum as an intermediary parameter that bridges the gap between existing control system operations and impeller stall detection. By analyzing the frequency characteristics of the control error signal, the system can detect impeller stall conditions without requiring direct mechanical intervention or additional complex hardware.
2Stability of the object's composition
If the surge boundary control curve is adjusted downward to restore stability, then control instability is resolved, but the operational cooling capacity is reduced
Solution Approach 1:
The patent implements dynamic adjustment of the surge boundary control curve based on real-time impeller stall detection. Rather than using a fixed conservative curve that permanently limits capacity, the system dynamically modifies the curve downward only when impeller stall is detected, allowing full cooling capacity during normal operation while maintaining stability during stall conditions.
Solution Approach 2:
The patent changes the operational parameters of the surge boundary control curve based on detected impeller stall conditions. By adjusting the curve position (a key parameter) in response to real-time system state, the system optimizes the trade-off between stability and cooling capacity, maintaining maximum capacity when stable and preventing instability when stalled.
3Measurement precision
If high frequency signal content is used to detect impeller stall, then detection precision is improved, but the complexity of signal analysis increases
Solution Approach 1:
The patent replaces complex physical measurement systems with mathematical signal processing of existing control signals. By using frequency spectrum analysis (Fast Fourier Transform) on the control error signal, the system achieves high detection precision through computational methods rather than additional complex hardware, resolving the contradiction between precision and complexity.
Data Source
AI summary
Methods and systems for detecting and recovering from control instability caused by impeller stall in a chiller system are provided. In one embodiment, an impeller stall detection and recovery component of a chiller control unit calculates a control error signal frequency spectrum for an evaporator leaving water temperature, determines whether a high frequency signal content of the control error signal frequency spectrum exceeds acceptable limits, and adjusts a surge boundary control curve downward by a predetermined incremental value in order to resolve instability caused by impeller stall.