• 설비공학논문집
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• 제12권7호
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• pp.649-658
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• 2000

Thermodynamic modeling of low-pressure scroll compressor was developed by combining continuity and energy conservation equation. Suction gas heating was considered using energy balance inside the low pressure shell. Pressure, temperature and mass of refrigerant-22 as a function of orbiting angle were calculated by solving the governing equations using fourth order Rung-Kutta scheme. Motor efficiency was taken by experiments with a variation of frequency. The developed model was applied to the analysis of an inverter driven scroll compressor with a variation of frequency, pressure ratio and operating conditions. The model was verified with the experimental results at the same operating conditions. The developed model was adequate to predict performance of the inverter driven scroll compressor as a function of operating conditions. Calculated parameters from the model were discharge temperature, mass flow rate, power input, COP, and thermodynamic properties with respect to orbiting angle. To enhance the performance of a scroll compressor, it is essential to diminish leakage at low frequency level and improve the mechanical efficiency at high frequency level.

• 한국초전도ㆍ저온공학회논문지
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• 제5권1호
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• pp.111-117
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• 2003

In the design of the split type free displacer Stilting cryocooler the motion of the displacer is very important to decide the cooling capacity, which depends upon the working gas pressure, the swept volume in the compression space and the expansion space, operating frequency, the phase shift between piston and displacer, etc. In this study, Stirling cryocooler actuated by the electric farce of the dual linear motor is designed and manufactured. Cool down characteristics of the cold end with laser displacement sensor in the expander of the Stilting cryocooler is evaluated. The charging pressure was 15kg$_{f}$/$\textrm{cm}^2$ and operating frequency was 50Hz. Input power and the lowest temperature were about 32W and 67K, respectively. And, displacement of the piston is measured by LVDTs (Linear Variable Differential Transformers), displacement of thedisplacer is measured by laser optic method, and phase shift between piston and displacer is discussed. As the peak-to-peak pressure of the compressor was increased, peak-to-peak displacement of the displacer was increased. The peak-to-peak displacement of the displacer increases in the range of 0 - 64.5Hz(resonant frequency of the displacer), but decreases steeply when the operating frequency is bigger than the resonant frequency. Finally when the phase shift between displacements of the Piston and displacer is 45。, operating frequency is optimum and is decided by resonant frequency of the expander, mass and cross section area of the displacer and constant by friction and flow resistance.e.

• 전자공학회논문지CI
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• 제45권1호
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• pp.78-85
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• 2008

대부분의 전력 관리 기법에 대한 연구는 동작 주파수나 동작 전압을 변화 시켜 시스템의 가용성을 증가시키는데 집중되었다. 이 방법은 전력소모를 줄이기 위해 구동 주파수를 수시로 변경하므로 실 시스템의 성능을 저하 시킨다. 소비 전력을 줄이기 위한 다른 방법은 구동 주파수의 개수를 제한하거나 실행 시간 동안 전체 주파수를 완만하게 관리하여 시스템의 성능을 높이는 것이다. 허나 기존 연구는 실시간 응용 프로그램에는 적합하지 않다. 본 논문에서는 실시간 시스템에서 소비 전력의 손실을 줄이고 시스템의 성능을 향상시키기 위해 구동 주파수 레벨의 할당 방법과 주파수 평활화 기법을 이용한 전력 관리 기법을 제안한다. 이 기법은 연속적인 주파수 간격에서 알고리즘이 예측한 주파수를 양자화된 주파수로 매핑한다. 이러한 주파수 평활화 기법은 좁은 주파수 대역에서 잦은 주파수 변경으로 발생한 시스템의 오버헤드를 줄일 수 있다. 매핑된 주파수는 넓은 주파수 간격에서 주파수 불일치로 발생하는 전력소모를 줄일 수 있다. 모의실험을 통하여 제안한 알고리즘이 기존의 CC RT-DVS 기법에 비해 최대 40%, 평균 15% 정도 소비 전력을 줄일 수 있었다.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1987년도 한국자동제어학술회의논문집; 한국과학기술대학, 충남; 16-17 Oct. 1987
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• pp.597-602
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• 1987

This paper proposes a voltage-fed high frequency resonant inverter having variable voltage variable frequency(VVVF) control function. VVVF control is performed by PWM-TRC method in the boost type chopper and PFM-TRC method in the high frequency resonant inverter. This circuit is suitable for induction heating and melting power supply in industry. The operating characteristics of this inverter are discussed from a theoretical point of view. The results of operating characteristic analyses are given leading to complete designing data.

• 한국초전도저온공학회:학술대회논문집
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• 한국초전도저온공학회 2002년도 학술대회 논문집
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• pp.63-66
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• 2002

A free piston and free displacer (FPFD) Stilting cryocooler for the cooling infrared and cryo-sensor is currently under development at Korea Institute of Machinery & Materials. In this study, the dynamic characteristics of the displacer in the expansion space of the Stirling cooler was investigated by experiment. The experimental results show that the Stirling cryocooler has maximum cooling capacity at the certain relation between operating frequency and natural frequency of the displacer and the operating frequency of the Stirling crycooler should be determined by natural frequency of the linear compressor and displacer.

• 전기학회논문지P
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• 제64권4호
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• pp.261-266
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• 2015

This paper presents a newly proposed prototype of voltage-fed half-bridge partial resonant zero voltage switching PWM inverter operating at a constant frequency variable power regulation scheme, which is more suitable and acceptable for induction heated(IH) cooking appliances. This application-specific high frequency inverter circuit topology using a new generation specially-designed IGBTs can operate under a principle of a fixed frequency ZVS-PWM strategy. The operating principle of a new partial resonant inverter circuit is described on the basis of its computer-aided simulation analysis, its including steady-state operating characteristics.

• 한국초전도ㆍ저온공학회논문지
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• 제4권2호
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• pp.58-62
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• 2002

The purpose of this study is to analyze the charging gas effect on the resonance and performance characteristics of the linear compressor for small scale FPFD Stirling refrigerator. To ensure high performance of FPFD type Stirling refrigerator, the operating frequency of the refrigerator should be around the natural frequency of compressor. The gas spring effect which is induced from Pressure change in cylinder due to motion of pistons has significant effect on the natural frequency of the compressor. The numerical results show the linear compressor has high natural frequency when the charging pressure of working fluid is high and the stroke of compressor, current, input power and efficiency of compressor were shown with different operating conditions.

• 전력전자학회논문지
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• 제25권6호
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• pp.451-458
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• 2020

In this study, a trade-off analysis of a power conversion system (PCS) is performed in accordance with a power semiconductor device to establish the suitable operating frequency range for the anyplace induction heating system. A resonant network is designed under each operating frequency condition to compare and analyze the PCS losses depending on the power semiconductor device. On the basis of the simulation results, the PCS losses and frequency condition are calculated. The calculated results are then used for a trade-off analysis between Si-MOSFET and GaN-HEMT based on PCS. The suitable operating frequency range is determined, and the validity of the analysis results is verified by the experiment results.

• Journal of Power Electronics
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• 제18권4호
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• pp.1268-1277
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• 2018

A relatively high operating frequency is required for efficient wireless power transfer (WPT). However, the alternating current (AC) resistance of coils increases sharply with operating frequency, which possibly degrades overall efficiency. Hence, the evaluation of coil AC resistance is critical in selecting operating frequency to achieve good efficiency. For a Litz wire coil, AC resistance is attributed to the magnetic field, which leads to the skin effect, the proximity effect, and the corresponding conductive resistance and inductive resistance in the coil. A numerical calculation method based on the Biot-Savart law is proposed to calculate magnetic field strength over strands in Litz wire planar spiral coils to evaluate their AC resistance. An optimized frequency can be found to achieve the maximum efficiency of a WPT system based on the predicted resistance. Sample coils are manufactured to verify the resistance analysis method. A prototype WPT system is set up to conduct the experiments. The experiments show that the proposed method can accurately predict the AC resistance of Litz wire planar spiral coils and the optimized operating frequency for maximum efficiency.

• Journal of Power Electronics
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• 제10권6호
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• pp.777-783
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• 2010

In order to drive gas discharge lamps, DC-AC converters with a LCC resonant tank, whose output voltage is adjusted by a variable frequency control are frequently used. However, when they are activated by varying the operating frequency, converters are frequently damaged by unstable operation, due to the rising and falling of the operating frequency near the resonant frequency. To solve this problem, a simple protection circuit for the power supply of a gas discharge lamp is proposed in this paper. This circuit senses the primary current of the main transformer. Using this protection circuit, the operating frequency of the lamp driving inverter system is kept close to and on the right side of the resonant frequency and the inverter is always operated in the ZVS condition. The resulting stable variable frequency operation allows various gas discharge lamps to be tested without the risk of damaging the main switches, because the protection circuit can protect the power MOSFETs of bridge converters from abnormal conditions. The validity and effectiveness of the proposed protection circuit are verified through the experimental results.