Moving-coil Linear Compressor Research Articles

Experimental study of DC excitation effect on the performance of moving coil linear compressor

In this paper, a novel Multi-loop Moving Coil Linear Compressor (M-MC-LC) is studied, in which the piston is driven by the Co-core Bilateral Reverse Coil (CBRC) in a reciprocating motion within the magnetic array. The DC excitation technique is introduced to address the phenomenon that the piston is axially offset under the influence of gas force. In order to clarify the effect of DC excitation on the performance of the moving-coil linear compressor, the compressor prototype is developed, and the dynamic performance testing test-bed and the refrigeration performance test-bed are built to qualitatively and quantitatively analyze the relevant performance parameters of the compressor from theoretical and experimental aspects. The results show that when the DC excitation accounts for less than 20% of the total input voltage, the pressure ratio increases with the increase of DC excitation; when the percentage is at 22.9%, a sudden drop in the volumetric efficiency of compressor occurs. Mass flow and COP increases first and then decreases with the increase of DC voltage excitation. The study results provide a guideline for the stable and reliable operation of the system and provide a valuable reference for the linear compressor piston offset adjustment.

Simulation Study on Direct-Drive Compressor with Electromagnetic Linear Actuator

In order to enhance compressor efficiency and meet the requirements of energy conservation and environmental protection, this study designed a direct-drive compressor with an electromagnetic linear actuator. Starting with the structural design and performance analysis of the linear compressor, the working process of the moving-coil linear compressor was analyzed. The basic performance of the designed moving-coil linear motor was simulated and analyzed using the Maxwell software, while the overall performance of the linear compressor was simulated and analyzed using the Simulink software to verify the feasibility of controlling a linear compressor via the direct drive of a linear motor.

Experimental research on performance of an oil-free moving-coil symmetrical dual-piston linear compressor for the J - T throttle refrigerator

In order to improve the efficiency of the Joule-Thomson (J-T) throttling refrigerator, an oil-free symmetrical dual-piston moving-coil linear compressor was developed, and its principle was demonstrated in detail. As the core component of the J-T throttling refrigerator, the linear compressor provides the pressure ratio and mass flow rate required by the throttling cycle. The linear compressor prototype was tested with nitrogen to evaluate its performance at different pressure ratios, strokes, and driving frequencies. Key performance parameters have been obtained, and the experimental results show that the input power is 175.2 W, the mass flow is 1.128 g/s, the unit power mass flow is 6.438 mg/s/W, the motor efficiency, volumetric efficiency, isentropic efficiency, and isothermal efficiency is 87.7%, 81.5%, 74.9%, and 63.7% at the design parameter (pressure ratio of 3.0, stroke of 10.0 mm, frequency of 60.0 Hz), respectively. The maximum mass flow rate is 1.742 g/s, and the maximum motor efficiency, volumetric efficiency, isentropic efficiency, and isothermal efficiency is 88.1%, 94.0%, 81.2%, and 73.4%, respectively. The symmetrical dual-piston linear compressor brings large-capacity and high efficiency, which provide a useful attempt and reference for the optimization of the linear compressors for the J-T throttling refrigerator.

Study of the moving offset characteristics of multi-loop moving coil linear compressor

In this paper, a novel Multi-loop Moving Coil Large Output Volume Linear Compressors (M-MC-l-LC, Max 381.3cc) is proposed. A Co-core Bilateral Reverse Coil(CBRC) and a new Halbach permanent magnet ring array structure are proposed for the first time and applied to the development of prototype. The M-MC-l-LC electromagnetic force calculation equation is derived, the moving offset characteristics under different pressure ratios are studied, and a mathematical model that can reflect the moving offset law is established. Introduction the DC offset control method to solve the moving offset problem. Development the M-MC-l-LC prototype and construction a dynamic test rig for compressors. Experimental results show that increasing DC voltage countervails the moving offset and significantly increases the discharge pressure. The theoretical error of moving offset is within 8% and the mechanical efficiency of prototype is approximately 11.4% higher than that of the conventional compressor. The results of study have theoretical and practical implications for other linear compression moving offset analysis and accurate regulation of refrigeration capacity.

Experimental and Theoretical Investigation of Nonlinear Dynamic characteristics in an Oil-free Moving Coil Linear Compressor

The gas pressure, piston displacement and current response characteristics of an oil-free moving coil linear compressor driven by sinusoidal voltages at different frequencies have been experimentally studied. The results show that the response curves of gas pressure, piston displacement and current have nonlinear distortions deviating from the sinusoidal waveform. Among them, the piston displacement waveform has relatively small deviation from sinusoid, and the total harmonic distortion rate (THD) of piston displacement has a maximum value of 6.2% at 50Hz; the current waveform has relatively large deviation from sinusoid, and the THD of current has a maximum value of 73.7% at 60Hz. At this time, the current has two peaks in one cycle. It was analyzed that the nonlinear distortion of displacement and current occurs only in the compression process in a working cycle. In addition, a nonlinear dynamic model based on MATLAB software was established to analyze current distortion. The simulated values of gas pressure, piston displacement and current curves have a good coincidence with measured values. Finally, it is present that the severe distortion of the current curve is mainly caused by the non-linearity of the gas pressure.

Challenges in implementation of a moving coil linear compressor in a household refrigerator

A linear compressor is well known for its excellent performance in Stirling cryocooler, space application. Minimum linkages, lesser friction points and lower noise characteristics make the linear compressor more promising in the space application. The same technology has not emerged as an alternative compression technology for ground applications such as home refrigerators, air conditioners, electronic cooling. This paper discusses the challenges observed during the implementation of the moving coil linear compressor in home refrigerators. The prototype moving coil linear compressor has been developed and tested by integrating to the home refrigerator.

Theoretical modeling and experimental verification of the motor design for a 500 g micro moving-coil linear compressor operating at 90–140 Hz

This paper presents the theoretical modeling and experimental verification of the motor design for a micro moving-coil dual-opposed linear compressor operating at 90–140 Hz. A three-dimensional model is built to study the characteristics of its magnetic field and then the magnetic circuit configuration is optimized theoretically. The non-uniform distribution of magnetic field will have an important effect on the direction of the motor force, thereby decreasing the efficiency. Based on theoretical analyses, a 500 g micro linear compressor is built and then coupled with a given micro pulse tube cold finger to test the performance. Experimental results show that the developed compressor achieves an average motor efficiency of 78.6%, and a cooling power of 1.2 W at 77 K is acquired with an electric input power of 60 W. The experimental results of both linear motor and the cooler system are compared with the theoretical ones and good agreements can be observed.

Investigations on the three-stage gas-coupled Stirling-type pulse tube cryocooler

This paper establishes a theoretical model of the three-stage gas-coupled SPTC based on the electrical circuit analogy (ECA) model. A further improved ECA model for the three-stage arrangement is proposed to achieve the dynamic pressure and volume flow rate at any position of each stage, in which the effects of both the real gas and the dynamic temperature are considered to improve the accuracy. The temperature profiles in regenerators are studied by considering the temperature-induced enthalpy flow rate. Based on the above theoretical analyses, a gas-coupled three-stage SPTC driven by a moving-coil linear compressor is developed and tested. A no-load temperature of 4.8 K and cooling capacity of 40 mW/6 K are achieved experimentally with a total input power of 320 W, which is a considerable improvement of performance compared with the thermally-coupled three-stage SPTC counterpart developed by the same authors.

Theoretical and experimental investigations on a 12 kW Oxford-type dual-opposed moving-coil linear compressor

This paper presents theoretical and experimental investigations on an Oxford-type dual-opposed moving-coil linear compressor aiming to achieve an electric input power capacity of 12 kW, which is a great challenge in the moving-coil compressor field. A linearized model is established in which systematic analyses about force balance, mechanical resonance and magnetic circuit are conducted. The relations between air gap and magnetic field intensity in the magnetic circuit are focused on to optimize the motor efficiency, and the design of linear motor and mechanical spring are discussed in a more detailed way. The prototype compressor is worked out and tested, and experimental results are compared with theoretical analyses. The developed compressor will be coupled with a coaxial pulse tube cold head, which is expected to provide 600 W of cooling power at 77 K for cooling the high temperature superconducting (HTS) cables.

Investigations on a Three-dimensional Model of the Moving-coil Linear Motor Applied in the Space-borne Micro Compressor

In order to optimize the magnetic circuits of the linear motor applied in the space-borne pulse tube cryocooler, a three-dimensional magnetostatic field model of the moving-coil linear motor in the micro compressor is established. The effects of several key dimensions on the distributions of the magnetic flux density inside the air gap are simulated and discussed by finite element method. The simulated results show that the magnetic flux density decreases with the increase of both width and thickness of air gap. According to the analysis, it will greatly facilitate the design, fabrication and future practical applications of the micro moving-coil linear compressor.

Effects of the driving voltage waveform on the performance of the Stirling-type pulse tube cryocooler driven by the moving-coil linear compressor

The effects of three typical waveforms, namely, sine, trapezoid and smeared sine, on the performance of the Stirling-type pulse tube cryocooler (SPTC) driven by the moving-coil linear compressor are analyzed and studied experimentally. The results indicate that the dynamic pressure at the inlet of the cold finger has a weak relation with the driving voltage waveform, but the latter plays an important role in affecting both the motor efficiency and the SPTC cooling performance. In the tested range, either the cooling efficiency or the motor efficiency under the smeared sine waveform is the highest, while that under the sine waveform is the lowest. Moreover, given that the input power is below 30 W, the motor efficiencies under both smeared sine and trapezoid waveforms exceed 90%, which suggests a promising approach to achieve a linear compressor with a very high motor efficiency by optimizing the voltage waveform.

Theoretical and experimental investigations on the optimal match between compressor and cold finger of the Stirling-type pulse tube cryocooler

The match between the pulse tube cold finger (PTCF) and the linear compressor of the Stirling-type pulse tube cryocooler plays a vital role in optimizing the compressor efficiency and in improving the PTCF cooling performance as well. In this paper, the interaction of them has been analyzed in a detailed way to reveal the match mechanism, and systematic investigations on the two-way matching have been conducted. The design method of the PTCF to achieve the optimal matching for the given compressor and the counterpart design method of the compressor to achieve the optimal matching for the given PTCF are put forward. Specific experiments are then carried out to verify the conducted theoretical analyses and modeling. For a given linear compressor, a new in-line PTCF which seeks to achieve the optimal match is simulated, designed and tested. And for a given coaxial PTCF, a new dual-opposed moving-coil linear compressor is also developed to match with it. The simulated and experimental results are compared, and fairly good agreements are found between them in both cases. The matched in-line cooler with the newly-designed PTCF has capacities of 4–11.84W at 80K with higher than 17% of Carnot efficiency and the mean motor efficiency of 81.5%, and the matched coaxial cooler with the new-designed compressor can provide 2–5.5W at 60K with higher than 9.6% of Carnot efficiency and the mean motor efficiency of 83%, which verify the validity of the theoretical investigations on the optimal match and the proposed design methods.

Dynamic and thermodynamic characteristics of the moving-coil linear compressor for the pulse tube cryocooler: Part B – Experimental verifications

Experimental investigations are carried out to verify the theoretical analyses and modeling conducted in Part A. Some empirical corrections are made and two sets of experiments are arranged based on the same compressor coupled with two different coaxial cold fingers typically operating at 80 K and 60 K, respectively. The variations of φ, ΔP, I, θ; the input electric power, ηmotor; the cooling capacity and ηCarnot with the operating frequency at the given cooling temperatures are tested and compared with the simulation results, and fairly good agreements are found in both cases. The effects of the cooling temperature on these characteristics are also tested and discussed. Experimental results verify the validity of the theoretical investigations in Part A. The results also indicate that the theoretical studies can apply to wide ranges of both the operating frequency and the cooling temperature.

Dynamic and thermodynamic characteristics of the moving-coil linear compressor for the pulse tube cryocooler. Part A: Theoretical analyses and modeling

Theoretical analyses and modeling are conducted on dynamic and thermodynamic characteristics of the moving-coil linear compressor in the Stirling-type pulse tube cryocooler. Governing equations are deduced, and φ and ΔP are found to be the two key parameters connecting compressor to pulse tube cold finger. An improved ECA model is developed to investigate the cold finger characteristics and their influences on φ, ΔP. Systematic simulations based on a specific case are performed to provide elaborate explanations about the theoretical analyses with the frequency varying from 30 Hz to 100 Hz at 60 K, 80 K and 100 K, respectively. The variations of four important parameters of φ, ΔP, I and θ, and the compressor thermodynamic performances and the cryocooler cooling performances, with the frequency at above temperatures are simulated and analyzed, respectively. The effects of compressor geometrical parameters on ηmotor are also simulated. The experimental verifications will be presented in Part B.

Design and analysis of novel moving-coil linear compressor for air brake system in electric vehicles

This paper presents a novel direct-drive linear compressor for air brake system in electric vehicles. By integrating the free piston and mechanical springs into a moving-coil type electromagnetic linear oscillating actuator (EMLOA), the structure of the proposed linear compressor is increasing compact. Moreover, the novel features, such as high thrust force constant, better controllability, and high resonant frequency, enable the linear compressor to operate most efficiently at resonance. The thrust force constant is enhanced by employing quasi-Halbach array and is tested to be high (74 N/A) and unchanged over the whole stroke. Dynamic modeling and experiment validation are performed to analyze dynamic characteristics of the linear compressor. The experimental and simulated data agree well, by regulating the frequency and amplitude of the excitation current, the high efficiency of the EMLOA (91.7%) and the low energy volume ratio of the linear compressor (7.3 kW/(m 3 /min)) indicate that the proposed linear compressor is significant energy saving compared with conventional compressors.

Theoretical and experimental investigations on the dynamic and thermodynamic characteristics of the linear compressor for the pulse tube cryocooler

Theoretical and experimental investigations on the dynamic and thermodynamic characteristics of a linear compressor incorporating the thermodynamic characteristics of the inertance tube pulse tube cold finger have been made. Both the compressor and cold finger are assumed as a one-dimensional thermodynamic model. The governing equations of the thermodynamic characteristics of the working gas are summarized, and the effects of the cooling performance on the working gas in the compression space are discussed. Based on the analysis of the working gas, the governing equations of the dynamic and thermodynamic characteristics of the compressor are deduced, and then the principles of achieving the optimal performance of the compressor are discussed in detail. Systematic experimental investigations are conducted on a developed moving-coil linear compressor which drives a pulse tube cold finger, which indicate the general agreement with the simulated results, and thus verify the rationality of the theoretical model and analyses.

Theoretical and experimental investigations on the partial scaling method for the Oxford-type moving-coil linear compressor

This paper puts forward the partial scaling method of the Oxford-type moving-coil linear compressor for pulse tube cryocoolers and analyzes the related principles. The systematic experimental investigations are further made to verify the analyses. One of the typical compressors developed in the authors’ laboratory is chosen to be scaled, and then coupled with the original pulse tube cold finger. At the typical operating temperature of 80K for the pulse tube cold finger, the scaled compressor’s maximum input electric power increases from 236.7W to 370.0W, and the cooling power is enhanced from 10.0W to 15.0W. The motor efficiency decreases from 78% to 73%, but the average cooling efficiency slightly increases from 11% to 12% of Carnot efficiency due to a better match between scaled compressor and original cold finger. The rationality and feasibility of the partial scaling method have been verified by the theoretical analyses and experimental investigations.