• 한국전자파학회논문지
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• 제30권3호
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• pp.252-259
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• 2019

제트 엔진 변조(jet engine modulation: JEM) 신호는 제트 엔진 고유 정보인 날개 수를 제공하기 때문에 HRRP(High-Range Resolution Profile), ISAR(Inverse Synthetic Aperture Radar)와 함께 표적 인식 분야에서 널리 이용된다. 제트 엔진의 날개 수를 얻기 위해서는 날개 수에 비례하는 chopping 주파수를 추출하는 것이 중요하다. 기존의 chopping 주파수 추출 방법은 초기 문턱값(threshold)를 정의하고, 이를 줄여가며, chopping peak를 탐지하는 방법을 사용한다. 하지만 이러한 탐지 방법은 반복적 찾음에 따라 신호에 따라 시간이 많이 소요되는 단점을 가지고 있다. 이에 본 논문에서는 MUSIC(MUltiple SIgnal Classification) 알고리즘을 이용하여 chopping 주파수를 추출하는 것을 제안한다. 주어진 JEM 신호에 MUSIC 알고리즘을 적용하여 chopping 주파수를 찾아 날개 수 후보군을 정하고, 후보군들의 점수를 위한 다른 chopping 주파수 추출에도 MUSIC 알고리즘을 적용하도록 한다. 반복적으로 찾는 기존의 탐지 알고리즘과 달리, 한번에 찾아내기 때문에 정확한 chopping 주파수를 찾을 뿐만 아니라, 계산 시간도 줄일 수 있음을 입증하였다.

• 한국식품조리과학회지
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• 제24권5호
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• pp.706-712
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• 2008

This study was conducted to evaluate the sanitation level and use of dish cloths, chopping board, and drawer in the refrigerator in 50 university students' houses located in Seoul and Kyonggido. The survey questionnaire evaluated general information, frequency of the washing, cleaning method, drying method and the associated factors. The highest percentage of the cleaning and drying methods of dish cloths were “boiling(76.0%)”, and “dry in the kitchen or on the sink(78.0%)”, respectively. For the chopping board and drawer in the refrigerator, the highest percentage of cleaning method was “use detergent” and drying method was “dry in the kitchen”. The mean of coliforms for dish cloths, chopping board, and drawer in the refrigerator was 4.46${\pm}$1.95 log CFU/100 $cm^2$, 3.92${\pm}$1.64 log CFU/100 $cm^2$, 3.48${\pm}$2.01 log CFU/ 100 $cm^2$, respectively. Salmonella spp. were not detected from all samples. But E. coli were detected from dish cloths(4.0%) and S. aureus were detected from dish cloths(16.0%), chopping board(12.0%), and drawer in the refrigerator(8.0%). The results of microbiological test of kitchen utensils indicated that the sanitary conditions of dish cloths, chopping board, drawer in the refrigerator should be improve promptly.

• 전기의세계
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• 제24권6호
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• pp.92-96
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• 1975

A generalized theroretical method is developed to eliminate a given number of harmonics in AC chopper output waves. The results show that halfwave symmetric and sinusoidal symmetric chopping are required to eliminate all even numbers of harmonics and , at least, M+1 times per half cycle chopping is required to eliminate any M odd number of harmonics in the given effective value of the output wave.

• 수산해양교육연구
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• 제12권2호
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• pp.142-151
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• 2000

The studies on the electronic control fuel injection system for a DI diesel engine have done for reducing the exhaust emission and improving fuel consumption. The electronic control fuel injection system is classified into a common rail system, a unit injector system and a high pressure injection system. The characteristics of these systems are largely depends on the operating characteristics of its solenoid that have high speed on-off operation. In order to improve these characteristics of fuel injection system, it is necessary to design the optimal shape of solenoid and select the input method of its power source. It was proposed HELENOID, COLENOID, DISOLE, and Multipole Solenoid in the studies of design for the optimal shape of solenoid. The studies on the energizing method, input method for power of solenoid were dealt with the conventional energizing method, the chopping method and the pre-energizing method. In order to find out the high response characteristics of solenoid, it is necessary to test the performance of optimally designed solenoid with a new energizing method. In this paper, the solenoid of multi-pole type with plat armature and its power control unit to control input current by the chopping method designed, and its response tests were performed according to its energizing conditions. As a result, the maximum input current for solenoid was controlled by the period of first stage exciting current and chopping duty ratio of control stage exciting current, and the fastest "on" time was able to get 0.46ms. The conditions of fastest "on" time was 0.3ms for first stage exciting current, 0.16ms for control exciting current and 75% for chopping duty ratio.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2007년도 추계학술대회 논문집 전력기술부문
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• pp.78-80
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• 2007

The residual flux in transformer's iron cores leads to a distortion of short-circuit current occasionally. And some considerable distortion may have effect on the validation of the test results. To avoid the substantial distortion, a suitable pretest is performed before the actual test. In case of applying this method there must be excessive overvoltage due to switching of an unloaded transformer and chopping of an excitation current. The purpose of this paper is estimate that the effect of the overvoltage results from this phenomenon on insulation performance of short-circuit transformer.

• 대한물리의학회지
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• 제16권4호
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• pp.77-83
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• 2021

PURPOSE: This study examined the changes in the respiratory function when PNF chopping and lifting patterns were used in chronic stroke patients METHOD: The subjects were 30 patients diagnosed with chronic stroke. The respiratory function (FVC, FEV₁, and FEV₁/FVC) were measured by spirometry. Thirty subjects were divided randomly into an experimental group to which 15 PNF chopping and lifting were applied and a control group to which chest breathing exercise was performed. The intervention was conducted three times a week for six 6 weeks. To examine the effects of intervention, the pre- and post-intervention values for each group were compared using a paired t-test. An independent t-test was used to compare the differences in the values of changes pre- and post-intervention in the two groups. Statistical significance was set to .05. RESULTS: Satistically significant differences in FVC and FEV₁ were observed in both the experimental group and control group according to the intervention (p < .05). A statistically significant difference was found in FVC and FEV₁ compared to values of changes pre- and post-intervnetion between the experimental and control groups. There was no difference in FEV₁/FVC. CONCLUSION: The results suggest that PNF chopping and lifting can be applied as an excellent respiratory intervention program compared to general chest breathing exercises to improve respiratory function in stroke patients.

• 전기학회논문지
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• 제65권9호
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• pp.1597-1604
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• 2016

The speed at which the SRM (Switched Reluctance Motor) makes a transition from chopping control to single pulse operation. (i.e., low speed to high speed operation). It is unsatisfied with performance at all operational regimes. In this paper, the operational performance of SRM can be improved by using current hysteresis control method. This method maintains a generally flat current waveform. At the high speed, the current chopping capability is lost due to the development of the back-EMF. Therefore SRM operates in single pulse mode. By using zero-current switching and zero-voltage switching technique, the stress of power switches can be reduce in chopping mode. When the commutation from one phase winding to another phase winding, the current can be zero as fast as possible in this period because several times negative voltage of DC-source voltage produce in phase winding. This paper is compared to performance based on energy efficient C-dump converter topology and the proposed resonant C-dump converter topology. Simulation and experimental results are presented to verify the effectiveness of the proposed circuit.

• Journal of Power Electronics
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• 제15권6호
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• pp.1533-1546
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• 2015

This study presents a novel method for reducing the switching losses of an asymmetric half-bridge converter for a three-phase, 12/8 switched reluctance motor operated in low speed. In particular, this study aims to reduce the switching-off losses of chopping switches in the converter when operated in the current regulated mode (chopping mode). The proposed method uses the mixed parallel operation of IGBT (chopping switch) and MOSFET (auxiliary switch). MOSFET is precisely controlled to momentarily conduct prior to the turn-off interval of the IGBT. Consequently, the voltage across the switches is clamped to approximately zero, substantially decreasing the turn-off switching losses. The analytical expressions of power losses are extensively elaborated. Compared with the conventional asymmetric half-bridge converter, the modified converter can effectively minimize the switching losses. Therefore, the efficiency of the converter is eventually improved. Computer simulation and experimental results confirm the effectiveness of the proposed technique.

• 전기학회논문지P
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• 제57권2호
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• pp.72-78
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• 2008

The speed variation of SRM is fulfilled throughout a transition from chopping control to single pulse operation. (i,e., low speed to high speed operation). It is unsatisfied with performance at all operational regimes. In this paper, the operational performance of SRM can be improved by using current hysteresis control method. This method maintains a generally flat current waveform. At the high speed, the current chopping capability is lost due to the development of the back-EMF. Therefore SRM operates in single pulse mode. By using zero-current switching and zero-voltage switching technique, the stress of power switches can be reduce in chopping mode. When the commutation from one phase winding to another phase winding, the current can be zero as fast as possible in this period because several times negative voltage of DC-source voltage produce in phase winding. This paper is compared to performance based on conventional C-dump converter topology and the proposed resonant C-dump converter topology. Simulation and experimental results are presented to verify the effectiveness of the proposed circuit.

• Journal of Power Electronics
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• 제7권1호
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• pp.64-71
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• 2007

This paper proposes a novel active frequency drift (AFD) method to improve the islanding detection performance with minimum current harmonics. To detect the islanding phenomenon of grid-connected photovoltaic (PV) inverters concerning the safety hazards and possible damage to other electric equipment, anti-islanding methods have been described. The AFD method that uses chopping fraction (cf) enables the islanding detection to drift up (or down) the frequency of the voltage during the islanding situation. However, the performance of the conventional AFD method is inefficient and causes difficulty in designing the appropriate cf value to meet the limit of harmonics. In this paper, the periodic chopping fraction based on a novel AFD method is proposed. This proposed method shows the analytical design value of cf to meet the test procedure of IEEE Std. 929-2000 with power quality and islanding detection time. To verify the validation of the proposed method, the islanding test results are presented. It is confirmed that the proposed method has not only less harmonic distortion but also better performance of islanding detection compared with the conventional AFD method.