Translated Abstract
Due to the increasing interests in energy conservation and environment protection, the traditional reciprocating-type compressor which has a complex structure, high friction power loss and increasing cost can no longer satisfy the market demand. Such compressor also has limited space for proving the efficiency because it uses a crankshaft mechanism to convert the rotating of an electric motor into reciprocating motion to drive a piston. In consequences, the piston compressor driven by linear motor is introduced to meet the active demand for a high performance compressor.
Unlike the conventional reciprocating compressor which driven by a rotary motor coupled with a conversion mechanism, linear compressor is a new type of high performance compressor which is driven by moving-magnet linear motor. Therefore, it owns many advantages such as high mechanical efficiency, simple structure and convenient volume control. However, the linear compressor is difficult to control the piston stroke, top clearance distance and piston equilibrium position because of the free piston and no stroke limiter. Focusing on the technique difficulties of linear compressor and based on the thermodynamics, dynamics, electromagnetic and circuit theory, this paper mainly discussed the characteristics and the performance of the moving-magnetics linear compressor’s work process. In addition, the prototype of linear compressor and its piston displacement of self-sensor fuzzy control system are designed based on the theoretical and experimental study.
Linear compressor is a very typical electromechanical integrated system, involving the thermodynamics, dynamics, motor, electromagnetic, electrocircuit and so on, so the model of traditional reciprocating-type compressor can hardly satisfy the request of the linear compressor’s simulation and optimum design. In this paper, thermodynamic model, dynamic model, electromagnetic model, oil pump model and control model were established. Moreover, the characteristics of the piston movement, frequency, current, voltage and the indicating diagram were obtained through coupling solving the set of electromechanical equations.
The linear compressor’s piston stroke and the top learance distance have been varied, so does the equilibrium postion of the piston movement. Therefore, the piston displacement must be measured and controlled in order to improve the performance of linear compressor. In this paper, the mathematic model of the self-sensor was established by analyzing the moving magnet linear motor of linear compressor, and the measurement method of piston stroke was achieved. The piston stroke can be calculated by measuring the voltage and current of the linear motor coil. In order to effectively control the piston’s top clearance distance, the self-sensing fuzzy control system in the driving mode of variable time of flow were designed, and the control system’s steady and dynamic characteristics were studied. The experimental results show that the self-sensing fuzzy control system can effectively measure and control the piston stroke and the top clearance of the linear compressor, of which the steady-state error is smaller than 0.25mm and almost no overshoot nearby the TDC.
Based on the studies of characteristics and performance, the design methodology of linear compressor, which optimized the mechanism-spring resonance system, linear motor, suction and discharge valves, oil pump system and body’s damping system. The design methodology offers the foundation for the linear compressor’s industrialization and commercialization. Linear motor is the key part of the linear compressor and constitutes a great portion of the cost. At the same time, the linear motor influences the system’s performance. In this paper, the influence on the linear motor efficiency was analyzed. The design and machining methods of linear moving-magnet motor were discussed.
The experimental study was carried out on a moving-magnet linear compressor for refrigerator, and the movement characteristics, frequency response characteristics, voltage and current response characteristics and p-V indicator diagram were obtained. The simulation study was completed by properly choosen linear motor parameters, equivalent damping coefficient and capacitiance. The simulation results are in good agreement with experimental data, and the deviation of the simulation results from the experimental data is less than 10%, which is cause by the motor parameter’s veracity, suction and discharge pressure’s loss and pulsation and calibrated error of the triac’s time of flow, but it may completely satisfy engineering design’s demand.
The experimental and simulation results show the efficieny of linear compressor is influenced by the matching of operation frequency and natural frequency, operating condition, control system precision and and capacitiance. The results show that the natural frequency of linear compressor is influenced by not only mass of moving part and spring stiffness, but also discharge pressure and piston stroke, and increases with the discharge pressure. In the different discharge pressure and operation frequency, the compressor has the minimum working current and input power and higher efficiency when the operation frequency being close to the natural frequency. In designing the linear refrigerator compressor, the operation frequency should be equal to the natural frequency of the rated operating condition for the high performance of the linear compressor. Efficiency of the prototype of moving-magnet linear compressor for refrigerator was tested in the different conditions, and test results show COP is 1.75 in the standard test conditions.On the other hand, analyse the shortcomings of the prototype which should be improved in the future
Translated Keyword
[Linear compressorLinear motorSelf-sensorFuzzy control]
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