Compressor Control Using VFD and Mechanical Unloader for Efficiency
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Solution Overview
Problem
Existing compressor systems are inefficient in reducing capacity when load is below maximum capacity, as they either rely solely on variable frequency drives (VFDs) or mechanical unloaders, leading to suboptimal energy usage.
Innovation Solution
A control system that simultaneously utilizes variable frequency drives and mechanical unloaders to adjust compressor speed and capacity based on operational parameters like suction and discharge temperatures, optimizing energy efficiency by selecting efficient combinations of speed and unloading.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If only mechanical unloaders are used to reduce compressor capacity, then capacity can be reduced below maximum capacity, but energy efficiency is insufficient
Solution Approach 1:
The patent combines mechanical unloaders and variable frequency drives into a unified control system that operates them simultaneously rather than sequentially or independently. The controller coordinates both mechanisms to work together, merging their capacity reduction capabilities to achieve superior energy efficiency compared to using either system alone.
Solution Approach 2:
The system dynamically adjusts both compressor speed via VFD and mechanical unloading positions based on real-time operational parameters. The controller continuously monitors conditions and optimizes the combination of speed control and mechanical unloading, making the system adaptive rather than static.
2Productivity
If only variable frequency drives are used to reduce compressor speed, then capacity can be reduced, but energy efficiency remains suboptimal
Solution Approach 1:
The patent merges the variable frequency drive system with mechanical unloader systems, allowing both to operate simultaneously under coordinated control. This combination leverages the speed control capability of VFDs while adding the volumetric efficiency benefits of mechanical unloading, achieving better energy efficiency than VFD alone.
Solution Approach 2:
The system changes multiple operating parameters simultaneously - both compressor speed (via VFD) and mechanical unloading position (via slide valves or lifting valves). By adjusting these parameters in combination rather than singly, the system achieves more efficient operating points across the full range of capacity requirements.
3Productivity
If mechanical unloaders are used after VFD reduces speed to minimum level, then capacity can be reduced further, but this sequential approach is inefficient
Solution Approach 1:
The controller performs preliminary coordination of both VFD and mechanical unloaders from the outset, rather than waiting for VFD to reach minimum speed before engaging mechanical unloaders. This preliminary joint control allows the system to optimize the combination of both mechanisms across the entire operating range, avoiding inefficient sequential operation.
Solution Approach 2:
The system dynamically balances the contribution of VFD speed control and mechanical unloading based on real-time conditions. Rather than following a fixed sequence, the controller continuously adjusts both mechanisms to maintain optimal efficiency, making the control strategy adaptive to varying load conditions.
4Loss of energy
If compressor capacity is reduced without coordinated control, then energy savings can be achieved, but overcompression occurs
Solution Approach 1:
The control system incorporates feedback from operational parameters to monitor and adjust compressor operation. By continuously monitoring system conditions and using this feedback to coordinate VFD and mechanical unloader operation, the system prevents overcompression while maximizing energy savings, ensuring capacity reduction does not create harmful effects.
Data Source
AI summary
Control systems and methods for increasing efficiency of a compressor while the compressor capacity exceeds compressor load, by using a mechanical unloader such as a slide valve to reduce the internal volume ratio of the compressor and allow a more efficient speed to be maintained by a variable frequency drive (VFD) while reducing the compressor capacity based on the load. Control systems include the VFD, a controller for the VFD and the mechanical unloader, and temperature sensors. Compressor embodiments further include one or more compressors and mechanical unloaders operated by the control systems.