Linear Compressor Current Offset Control for Piston Position Tuning
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Solution Overview
Problem
Reciprocating compressors face a trade-off between efficiency and maximum freezing capacity due to frictional losses, where reducing initial piston value increases efficiency but decreases freezing capacity, and increasing it enhances freezing capacity but increases frictional loss and reduces efficiency.
Innovation Solution
A control module for linear compressors that generates an asymmetric motor current by applying a current offset to adjust the piston's initial position, allowing for increased freezing capacity while maintaining efficiency by optimizing the piston's push amount and using a virtual capacitor for resonance control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the initial piston value is reduced to decrease stroke, then frictional loss is reduced and compressor efficiency is improved, but maximum freezing capacity is reduced and overload handling becomes difficult
Solution Approach 1:
The patent applies dynamics by making the piston initial position adjustable rather than fixed. The controller dynamically changes the piston initial position based on operating conditions (normal vs. overload mode), allowing the system to optimize between efficiency and capacity as needed. This is achieved through asymmetric motor current control that electrically adjusts the piston starting position.
Solution Approach 2:
The patent changes the parameter of piston initial position to resolve the contradiction. By varying this parameter between a first value (for efficiency) and a second value (for capacity), the system can adapt to different operating requirements. The controller switches between these parameter values based on detected overload conditions.
2Productivity
If the initial piston value is increased to improve maximum freezing capacity, then freezing capacity is enhanced, but moving distance of the piston is increased causing increased frictional loss and reduced efficiency
Solution Approach 1:
The system dynamically adjusts the piston initial position based on operational demands. During normal operation, the piston starts from a position that minimizes stroke and frictional loss. When overload is detected, the controller switches to a different initial position that maximizes freezing capacity, thereby dynamically resolving the contradiction between capacity and efficiency.
Solution Approach 2:
The patent utilizes parameter changes by switching the piston initial position between two distinct values. This parameter switching allows the system to achieve high freezing capacity when needed while maintaining efficiency during normal operation, effectively resolving the trade-off between these two parameters.
3Adaptability or versatility
If voltage is varied to control freezing capacity, then freezing capacity control is achieved, but system complexity increases with multiple detectors and controllers
Solution Approach 1:
The controller performs multiple functions: it detects motor current, determines overload conditions, adjusts piston initial position, and controls motor operation. By consolidating these functions into a single multi-functional controller, the system achieves adaptability without proportionally increasing complexity. The same controller hardware handles various control tasks through software or control logic.
Solution Approach 2:
The patent merges the functions of current detection, overload detection, and piston position control into a single integrated control module. This consolidation reduces the number of separate components needed and simplifies the overall control architecture while maintaining the ability to control freezing capacity through asymmetric motor current adjustment.
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
The solution effectively increases the maximum freezing capacity and maintains compressor efficiency by electrically adjusting the piston's position and using a virtual capacitor for resonance control, ensuring stability and optimal performance.
Implementation Method 1
a piston is directly connected to a mover of a linear motor so as to perform a reciprocating motion in response to a linear motion of the motor
Implementation Method 2
at least one spring which is installed to elastically support the movable member in an axial direction
Data Source
Figure 1~2
Figure 3A~3B
Figure 4A~4B
AI summary
The control module includes a drive circuitry that drives the linear compressor based on a control signal, a detector that detects a motor current and a motor voltage corresponding to a motor of the linear compressor, an asymmetric current generator that generates an asymmetric motor current by applying a current offset to the detected motor current, and a controller that generates the control signal based on the asymmetric motor current and the detected motor voltage. Such a control module may increase a maximum freezing capacity by appropriately (or optimally) designing (setting) an initial value of a piston in a driving area or an operation area (or a high-efficiency driving area) of a compressor by considering the efficiency aspect, and executing an asymmetric operation in a high-load driving area (or a high freezing capacity driving area).