Chiller capacity control apparatuses, methods, and systems
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Solution Overview
Problem
Chillers with variable speed and variable geometry compressors face challenges in control efficiency and reliability due to conventional control techniques that can lead to unexpected aberrations and control limit cycles, failing to optimize chiller capacity and efficiency effectively.
Innovation Solution
A control system for chillers with centrifugal compressors and variable frequency drives, which determines chiller capacity commands, speed commands, and vane position commands to maintain operation near the surge control boundary for enhanced efficiency and controllability, while deviating from it to avoid aberrations and improve control stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional control techniques are used to maximize compressor efficiency by operating at or near the surge boundary, then compressor efficiency is improved, but control stability deteriorates due to unexpected aberrations and control limit cycles
Solution Approach 1:
The control system dynamically adjusts operating parameters based on real-time conditions, transitioning between following and deviating from the surge boundary as needed. The controller monitors system state and adaptively modifies speed and vane position commands to maintain stability while optimizing efficiency, rather than rigidly adhering to a fixed control strategy.
Solution Approach 2:
The system changes control parameters (speed command, vane position command) based on the operating point relative to the surge boundary. By adjusting these parameters dynamically and selectively deviating from the optimal efficiency trajectory when stability issues arise, the system resolves the contradiction between efficiency and control stability.
2Loss of energy
If the compressor operates at or near the surge boundary to maximize efficiency, then energy efficiency is improved, but controllability worsens due to unexpected control aberrations
Solution Approach 1:
The control system incorporates feedback mechanisms that monitor system response and detect aberrations. When control aberrations are detected near the surge boundary, the feedback loop triggers a deviation from the optimal efficiency path, adjusting speed and vane position commands to restore proper controllability while minimizing efficiency loss.
Solution Approach 2:
The controller proactively prevents control aberrations by detecting conditions that may lead to instability and adjusting operating parameters before aberrations occur. This preliminary anti-action allows the system to maintain efficiency near the surge boundary while preemptively avoiding controllability issues.
3Loss of energy
If control techniques follow the surge control boundary to optimize efficiency, then compressor efficiency is improved, but control complexity increases due to unexpected aberrations and limit cycles
Solution Approach 1:
The control strategy is segmented into different operational modes: following the surge boundary under stable conditions and deviating when aberrations are detected. This segmentation simplifies the overall control logic by breaking it into manageable segments rather than requiring a single complex continuous control algorithm to handle all scenarios.
Data Source
AI summary
Controls for chillers with variable speed and variable geometry compressors are disclosed. In exemplary embodiments, a centrifugal compressor equipped with a variable frequency drive and variable inlet guide vanes may be utilized. A controller is operable to determine a chiller capacity command, a speed command, and a vane position command. The speed command and vane position command may maintain system operation at or near a surge control boundary over one or more capacity ranges to enhance efficiency and deviate from the surge control boundary over certain capacity ranges to improve controllability or avoid control aberrations.