Linear Compressor Piston Control via Motor Current Estimation
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Solution Overview
Problem
Linear compressors face noise generation and operational instability due to collisions between the piston and the discharge valve during top dead center (TDC) control, which is inherent in existing feedback control methods, and require a more effective method to prevent these collisions without additional sensors.
Innovation Solution
A linear compressor with a valve plate discharge unit fixed to the cylinder and a pressure changing unit within the cylinder, where the controller uses real-time motor current and voltage data to detect pressure variations and control the piston's motion to avoid collisions by applying transformation equations to estimate the stroke and prevent TDC collisions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If feedback control is executed by detecting voltage and current to estimate piston stroke, then compressor operation control is achieved, but collision noise between piston and discharge valve is generated
Solution Approach 1:
The patent replaces the mechanical collision-based TDC detection method with an electromagnetic field-based approach. By measuring voltage and current signals from the linear motor, the controller estimates piston position and detects TDC without mechanical contact, thereby eliminating collision noise while maintaining operational control
Solution Approach 2:
The patent introduces an intermediary estimation process between the motor control system and the piston position. Instead of direct mechanical detection, the system uses voltage and current measurements as intermediaries to infer piston stroke and TDC position, preventing direct piston-valve collision while achieving control objectives
2Device complexity
If piston is reciprocated without mechanical locking, then linear motor direct drive is achieved, but piston collision with cylinder wall occurs under excessive voltage or load
Solution Approach 1:
The patent implements a feedback control system that continuously monitors voltage and current applied to the linear motor. Based on this feedback, the controller estimates piston position and adjusts motor control to prevent excessive displacement, thereby avoiding piston-cylinder wall collisions while maintaining the simple direct-drive structure
Solution Approach 2:
The patent performs preliminary estimation of piston stroke using voltage and current data before the piston reaches critical positions. This allows the control system to take preventive action by adjusting motor drive parameters, ensuring the piston remains within safe operational limits without requiring mechanical locking devices
3Object-generated harmful factors
If discharge unit with elastic member is used, then piston collision is absorbed, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent replaces the mechanical elastic member system with an electromagnetic control system. By using voltage and current measurements to estimate piston position and control motor output, the system eliminates the need for elastic absorption members, simplifying the discharge unit structure while still preventing harmful collisions
Solution Approach 2:
The control system uses the existing motor voltage and current measurements to serve dual purposes: both motor control and piston position detection. This self-service approach eliminates the need for additional sensors or mechanical cushioning components, reducing system complexity while maintaining collision prevention capabilities
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
This solution reduces noise and operational instability by preventing piston-discharge valve collisions, lowers the weight and cost of the discharge unit, and enables efficient compressor operation without additional sensors, enhancing the lifespan of components and reducing fabricating costs.
Implementation Method 1
a linear motor to supply a driving force for the motion of the piston
Implementation Method 2
a pressure changing unit to change a pressure applied to the piston or a variation rate of the pressure
Data Source
AI summary
A linear compressor is provided which is capable of reducing noise and fabrication costs. The linear compressor may include a piston that performs a reciprocating motion within a cylinder, a linear motor that supplies a driving force to the piston, a sensor that detects a motor voltage and motor current associated with the motor, a valve plate provided at one end of the cylinder to adjust a discharge of a refrigerant compressed in the cylinder, a pressure changing unit or device that changes a variation rate of pressure applied to the piston before the piston reaches the valve plate during the reciprocating motion, and a controller that determines whether the variation rate of the pressure applied to the piston has changed using the detected motor voltage and motor current, and controls the motor to prevent the piston from colliding with the valve plate on the basis of the determination result.