A novel moving magnet linear actuator is proposed for linear oscillations in the linear resonant compressors for household refrigerators. This paper provides stator and armature design including CAD model and geometric parameters. Furthermore, the working principle of the proposed actuator is explained. The stator assembly is composed of two reversely wound coils, which are electrically excited with single phase ac power and oscillates the radially magnetized armature. With the help of the electromechanical analytical model, the dynamic parameters such as stroke, velocity, and acceleration of the armature are derived. Additionally, the time-dependent current model of the stator winding is proposed. An experimental setup is used to validate these responses at the resonance excitation frequency with the help of sensors. The system kinetics are discussed to estimate the spring, damping, inertial, and magnetic forces. A simulation is executed to estimate the time-domain responses of these dynamic parameters and the effects of excitation frequency are discussed. The force models are experimentally validated at the resonance frequency excitation. In order to evaluate the performance of the proposed actuator, a comparison of the performance parameters, such as efficiency, stroke, current, and mass flow rate is demonstrated with the conventional rotary as well as the linear motors for linear compressor application.

Dynamic Analysis of a Novel Moving Magnet Linear Actuator

Linear compressors are becoming more widely utilized in refrigeration for their high efficiency in comparison with traditional rotary devices. The nature of the free piston in a linear compressor requires additional control which necessitates knowledge of the mechanical dynamics of the system. Sensorless control of the system is preferred for cost effectiveness. To this end, a pair of nonlinear observers have been developed to observe signals within the system dynamics and reduce the need for costly sensors. The first utilizes a current and voltage measurements to arrive at an observed velocity. The second utilizes a velocity measurement to arrive at observations of piston acceleration as well as a lumped uncertainty term in the mechanical dynamics. A stability analysis is presented to prove boundedness and convergence for these nonlinear observers with experimental results providing further validation. As these observers rely on accurate knowledge of the model parameters, to this end, an estimator has been designed to estimate the electrical parameters of the system. Experimental results validate this method as well.

Parameter Estimation and a Series of Nonlinear Observers for the System Dynamics of a Linear Vapor Compressor

Linear compressors have become more common in refrigeration applications due to their high efficiency. However, in order to achieve efficient and reliable operation of the machine, the system controller must be capable of dealing with two main issues. First, the nonlinear force of gas compression acting against the mass spring piston system causes the frequency at which system efficiency is maximized, i.e., the resonant frequency, to vary with the load. Second, the unconstrained piston stroke allows for the possibility of collision with the head, which may reduce reliability. Accounting for these issues requires knowledge of the piston dynamics; however, for reliability and cost effectiveness it is preferred to operate the system without the use of internal sensors. In this work a novel system level controller is designed to simultaneously achieve resonance-tracking and stroke control objectives utilizing a pair of nonlinear observers to obtain the necessary information sensorlessly. This design is validated under experimental testing, which demonstrates both the accuracy of the observed signals and the stability and convergence of the controller.

Sensorless Resonance Tracking and Stroke Control of a Linear Vapor Compressor Via Nonlinear Observers

The present invention relates to a linear motor for a linear compressor reciprocating a moving member linearly inside a stationary member to compress refrigerant, and more particularly, to a linear motor for a linear compressor capable of decreasing an iron loss of a flux generated when a current flows in a coil and increasing an inductance. A linear motor for a linear compressor includes an inner stator formed by stacking core blocks in a circumference direction to be insulated from each other, an outer stator formed by arranging core blocks in a circumference direction at a predetermined intervals, and winding a coil around the core blocks, and a plurality of permanent magnets formed between the inner stator and the outer stator with a predetermined gap, and reciprocated linearly due to a mutual electromagnetic force.

The linear motor of the linear compressor

In some applications, an indicator is needed for sudden system state changes, where the direct measurement of the system states is neither possible nor practical. In this brief, it is shown that the error of robust integral of the sign of the error observer can be used as an indicator of sudden system state changes. The application of this method for collision detection in a linear vapor compressor is investigated. Linear vapor compressors are becoming more widely utilized in cooling appliances, such as household refrigerators and portable coolers due to their high efficiency. The fact that the piston is free in a linear vapor compressor allows for the possibility of collisions between the compressor piston and other components of the linear vapor compressor within the compression chamber. Sensorless crash detection is preferred for purposes of reliability, ease of production, and cost effectiveness. For this purpose, a novel head crash detection scheme applying a nonlinear observer is developed. This scheme not only detects all head crashes accurately, but also provides an indicator proportional to the piston velocity at the time of impact. This indicator can be used to estimate how much the force command needs to be reduced to prevent further collision. A set of simulation and experimental test results validate the performance of the head crash detection scheme.

Impact Fault Detection for Linear Vapor Compressor Using RISE Observer

Linear compressors have been used in cooling apparatuses such as house refrigerators and portable coolers due to their high efficiency. The stroke of a free piston in a linear compressor driven by PWM inverter can be estimated by integrating the back electromotive force (EMF) of a linear permanent-magnet synchronous motor (LPMSM), which is used to drive a piston. However, it may be saturated due to dc offsets in measured motor voltage and current. The method for estimating precisely the piston stroke by using both the high-pass filter (HPF) and adaptive all-pass filter (APF) is suggested. The HPF is used for removing dc offset in the back EMF, and the resonance frequency of an adaptive APF is controlled in order to adjust the phase of back EMF to -90° under inverter frequency variations. Through simulation and the experimental results, it can be verified that the piston stroke has nearly sinusoidal waveform without any dc offset.

Method of estimating precise piston stroke of linear compressor driven by PWM inverter

Recently, the linear compressors with the free piston driven by the linear motor have widely attention in the cooling apparatus such as a refrigerator due to high efficiency. The method of using triacs as a linear motor drive is not satisfactory to improve the efficiency of the linear compressor. In this paper, the performance of the linear compressor using a PWM inverter such as the efficiency is investigated with the variations of both mechanical resonant frequency and electrical resonant frequency. The control loop for controlling both the piston stroke and efficiency is suggested. Through simulation and experimental studies, the performance of both the stroke and angle controls for improving the efficiency of the linear compressor is verified.

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Analysis and Efficiency Control of Linear Compressor System for Refrigerator Driven by PWM Inverter

This paper deals with an algorithm for controlling ac output voltage of Z-source inverter using Modified SVPWM (abbreviated as MSVPWM). Unlike the conventional space vector pulse width modulation, MSVPWM has one extra shoot-through zero time T sh . During shoot-through zero time, both switches in a leg are conducted simultaneously in order to boost inverter output voltage to any desirable value regardless the line voltage. The algorithm to control linearly the capacitor voltage is suggested to improve the performance of Z-source inverter system. The performance of Z-source inverter using above algorithms is demonstrated in simulation results using PSIM.”

Jang-Kyung Son

Papers

Method of estimating precise piston stroke of linear compressor driven by PWM inverter

Analysis and Efficiency Control of Linear Compressor System for Refrigerator Driven by PWM Inverter

The Algorithms for Controlling AC Output Voltage of Z-Source Inverter Using Modified SVPWM