• 한국기계가공학회지
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• 제19권6호
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• pp.1-8
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• 2020

This paper proposes a method for measuring friction forces and creating a friction model for a rotary motion control system as well as an autonomous vehicle testbed. The friction forces versus the velocity were measured, and the viscous friction, Coulomb friction, and stiction were identified. With a nominal PID (proportional-integral-derivative) controller, we observed the adverse effects due to friction, such as excessive steady-state errors, oscillations, and limit-cycles. By adding an adequate friction model as part of the augmented nonlinear dynamics of a plant, we were able to conduct a simulation study of a motion control system that well matched experimental results. We have observed that the implementation of a model-based friction compensator improves the overall performance of both motion control systems, i.e., the rotary motion control system and the Altino testbed for autonomous vehicle development. By utilizing a better simulation tool with an embedded friction model, we expect that the overall development time and cost can be reduced.

• Journal of Power Electronics
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• 제11권2호
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• pp.156-162
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• 2011

The control loop time delay caused by sampling, the zero-order-holder effect and calculations is inevitable in the digital control of dc-dc switching converters. The time delay will limit the bandwidth of the control loop and therefore degrade the transient performance of digital systems. In this paper, the quantization time delay effects with different time delay values based on a generic second-order system are analyzed. The conclusion that the bandwidth of digital control is reduced by about 20% with a one cycle delay and by 50% with two cycles of delay in comparison with no time delay is obtained. To compensate the time delay and to increase the control loop bandwidth, a duty ratio predictive control scheme based on linear extrapolation is proposed. The compensation effect and a comparison of the load variation transient response characteristics with analogy control, conventional digital control and duty ratio predictive control with different time delay values are performed on a point-of-load Buck converter by simulations and experiments. It is shown that, using the proposed technique, the control loop bandwidth can be increased by 50% for a one cycle delay and 48.2% for two cycles of delay when compared to conventional digital control. Simulations and experimental results prove the validity of the conclusion of the quantization effects of the time delay and the proposed control scheme.

• 한국통신학회논문지
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• 제36권7B호
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• pp.878-885
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• 2011

수중음향 통신은 대역이 제한되어 있고 음파가 해저 및 해수면에 반사되어 신호가 수신된다는 특성 때문에 신뢰성이 높고 전송속도가 빠른 수중음향 통신의 구현이 어렵다. 그러므로 최근의 수중 통신시스템에서 다수의 센서를 이용하는 MIMO 기술이 활발히 연구 중에 있다. 그러나 송수신단의 다중 센서를 이용한 수중통신에서의 MIMO 통신기술은 송수신단의 각 수신 센서에서의 상관값이 크기 때문에 다중 경로로 인하여 공간 다이버시티를 사용해 이득을 기대하기가 어렵다. 따라서 본 논문에서는 송신 센서는 두개를 설정하고 수신센서를 한 개로 하는 MISO 채널에서 부호화 기법으로는 LDPC 부호를 이용하여 채널 추정 보상 기법과 결합하여 성능을 분석하였다.

• 한국통신학회논문지
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• 제33권9A호
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• pp.882-890
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• 2008

본 논문은 ADC(analog-to-digital converter)의 속도에 의한 시간 영역에서 채널 추정 한계를 극복하기 위해서 트레이닝(training) 신호의 주파수 성분을 이용해서 다중경로 채널을 추정하고 이를 이용해서 채널 왜곡을 보상하는 BPM(biphase modulation)-UWB 수신기를 제안한다. 여러 개의 펄스로 구성된 펄스열의 주기적인 특성을 이용해서 효과적으로 채널 추정이 가능함을 수학적으로 보인다. 또한 추정된 채널 주파수 응답 정보를 이용해서 시스템 성능을 최적화시킬 수 있는 디지털 수신부 구조를 제시하며 BER성능을 유도한다. 시뮬레이션을 통해 제시된 방법이 다중경로 채널을 보상함으로써 수신기의 BER성능이 획기적으로 개선됨을 보인다.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2019년도 전력전자학술대회
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• pp.71-73
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• 2019

The output current of the Grid Connected Inverter (GCI) can be polluted with harmonics mainly due to i) dead time in switches, ii) non-linearity of switches, iii) grid harmonics, and iv) DC link fluctuation. Therefore, it is essential to design the robust Harmonic Compensation (HC) technique for the improvement of output current quality and fulfill the IEEE 1547 Total harmonics Distortion (THD) limit i.e. <5%. The conventional harmonic techniques often are complex in implementation due to their i) additional hardware needs, ii) complex structure, iii) difficulty in tuning of parameters, iv) current controller compatibility issues, and v) higher computational burden. In this paper, to eliminate the harmonics from the GCI output current, a novel Digital Lock-In Amplifier (DLA) based harmonic detection is proposed. The advantage of DLA is that it extracts the harmonic information accurately, which is further compensated by means of PI controller in feed forward manner. Moreover, the proposed HC method does not require additional hardware and it works with any current controller reference frame. To show the effectiveness of the proposed HC method a 5kW GCI prototype built in laboratory. The output current THD is achieved less than 5% even with 10% load, which is verified by simulation and experiment.

• 풍력에너지저널
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• 제9권4호
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• pp.47-56
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• 2018

This paper introduces an active power dependent standard characteristic curve, Q(P) to compensate for voltage variations due to the output of distributed generation. This paper presents an efficient control method of grid-connected inverters by comparing and analyzing voltage variation magnitude and line loss according to the compensation method. Voltage variations are caused not only by active power, but also by the change of reactive power flowing in the line. In particular, the system is in a relatively remote place in a coastal area compared with existing power plants, so it is relatively weak and may not be suitable for voltage control. So, since it is very important to keep the voltage below the normal voltage limit within the specified inverter capacity and to minimize line loss due to the reactive power. we describe the active power dependent standard characteristic curve, Q(P) method and verify the magnitude of voltage variation by simulation. Finally, the characteristics of each control method and line loss are compared and analyzed.

• 시스템엔지니어링학술지
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• 제17권2호
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• pp.49-60
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• 2021

The Core Protection Calculator System (CPCS) is vital for plant safety as it ensures the required Specified Acceptance Fuel Design Limit (SAFDL) are not exceeded. The CPCS generates trip signals when Departure from Nucleate Boiling Ratio (DNBR) and Local Power Density (LPD) exceeds their predetermined setpoints. These setpoints are established based on the operating margin from the analysis that produces the SAFDL values. The goal of this research is to create a simplified CPCS that optimizes operating margin for I-SMRs. Because the I-SMR is compact in design, instrumentation placement is a challenge, as it is with Ex-core detectors and RCP instrumentation. The proposed CPCS addresses the issue of power flux measurement with In-Core Instrumentation (ICI), while flow measurement is handled with differential pressure transmitters between Steam Generators (SG). Simplification of CPCS is based on a Look-Up-Table (LUT) for determining the CEA groups' position. However, simplification brings approximations that result in a loss of operational margin, which necessitates compensation. Appropriate compensation is performed based on the result of analysis. FPGAs (Field Programmable Gate Arrays) are presented as a way to compensate for the inadequacies of current systems by providing faster execution speeds and a lower Common Cause Failure rate (CCF).

• 항공우주정책ㆍ법학회지
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• 제24권1호
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• pp.35-58
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• 2009

항공기 운항 중 제3자에 대한 피해를 배상하는 국제 조약은 1933년 로마협약에서 처음 규정하였지만 호응을 얻지 못한 채 1952년 로마 협약으로 개정되면서 배상 금액이 상향 조정되는 등 일부 내용이 개선되었다. 이에 불구하고 2009년 현재 협약 당사국이 49개국에 불과하여 보편적인 국제 조약으로 기능하지 못하고 있는데 동 협약을 개선한 1978년 몬트리올 의정서는 배상 상한을 다시 인상하였음에도 불구하고 미국, 일본, 영국, 독일 등 주요 항공 대국이 참여치 않은 가운데 의정서 당사국이 12개국에 그치면서 명목을 유지하는 형편이다. 이에 따라 제3자에 대한 항공기 피해에 대한 배상은 사고 발생지 국내법에 의해 해결하는 추세이다. 2001년 발생한 9.11 테러 공격은 세계 최대 강국인 미국이라도 대규모 제3자 피해를 혼자 감당하기 어려운 것을 인식하게 된 가운데 국제민간항공기구(ICAO) 주도하에 국제사회 공동으로 향후 재발에 대비한 배상 체제를구축코자 ICAO 법률위원회의 수년간 작업 끝에 제3자 피해 배상에 관한 현대판 조약을 캐나다 몬트리올 외교회의에서 채택케 된 것이다. 과거 지상 제3자 피해 배상에 관한 협약과는 달리 공중 충돌로 제3자가 피해를 볼 경우도 포함시켜 '지상'이라는 표현이 협약 제목에서 삭제된 한편, 과거 협약이 항공기를 테러로 이용하여 제3자 피해가 발생할 것을 예상하지 못하였지만 금번 채택 협약은 9.11 사태와 같이 항공기를 이용한 테러공격으로 제3자 피해가 발생할 경우의 배상에 주안을 두었다. 그런 가운데 조약 제정 편의상 테러 공격에 의한 제3자 피해에 대한 배상을 위한 "불법방해배상협약"과 그렇지 않은 일반 위험 (general risks)으로 인한 제3자 피해 배상에 관한 "일반위험협약"으로 분리하여 2개의 조약을 외교회의의 컨센서스로 채택하였다. 상기 2개의 조약은 대규모 제3자 피해 발생을 염두에 두고 배상 상한을 대폭 인상하여 피해 배상을 현실화함과 동시에 신체적 피해로 인한 정신적 피해도 배상 대상에 포함시키면서 오늘날 항공운송 사고 시 승객에게 적용되는 조건을 제3자 피해자에게도 적용하는 등 조약의 내용을 현대화 시켰다. 그러나 "불법방해배상협약"은 대규모 피해에 대비한 배상금 충당을 위하여 "국제민간항공배상기금"을 창설하면서 어느 한 나라가 협약 당사국이 되느냐 마느냐에 따라서 협약이 운명이 좌우되게끔 하는 유별난 조항을 포함시켰다. 이는 미국을 염두에 둔 내용으로서 협약의 보편성을 해치는 한편, 일반적으로 국가가 배상책임을 지는 사안인 테러에 의한 피해 배상을 항공 산업에 있어서만 항공운송업자와 승객이 책임을 부담도록 하는 등의 독특한 내용들을 담고 있는 특징과 함께 협약의 장래 전망이 우려된다. 이는 국제 정치 현실상 몇 나라가 부담하는 테러 위험을 아무런 보상도 없이 여러 나라에 분산시키는 결과를 가져오는 내용이기 때문에 더욱 그러하다.

• 한국산업보건학회지
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• 제29권3호
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• pp.271-277
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• 2019

Objectives: A 46-year-old woman who had worked on cleaning stainless steel containers with Initially unknown powders died from acute silicosis. To determine whether the acute silicosis was related to his work environment, we conducted exposure assessment the level of exposure to respirable crystalline silica(RCS) during cleaning stainless steel containers with unknown powders. Methods: The exposure assessment of RCS were undertaken according to the National Institute for Occupational Safety and Health(NIOSH) method 7500. The components of the unknown powder were analyzed using X-ray Diffraction. Results: The unknown powder was found to be natural diatomaceous earth, which contained 12% and 9% quartz and cristobalite, respectively, crystalline silica. In the case of cleaning stainless steel containers with diatomaceous earth powder, the primary measurement resulted in 1.3 times higher occupational exposure limit of MOEL(in sum of quartz and cristobalite concentration) and 3.9 times higher in secondary measurement. The workbench was equipped with a local exhaust system, but because there was no hood at the end of the duct, the wind speed at the opening of the duct was 12 m/sec, whereas the controlled wind speed at the working position was only 0.3 m/sec below the legal standard. Conclusions: There is an urgent need to install the hood, conduct safety and health education for employers and workers, and periodically monitoring and manage the working environment.

• 전력전자학회논문지
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• 제27권5호
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• pp.376-383
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• 2022

The improved performance of computer parts, such as graphic card, CPU, and main board, has led to the need for power supplies with a high power output. The dynamic load profile rapidly changes the usage of power consumption depending on load operations, such as PC power and air conditioner. Under dynamic load profile conditions, power consumption can be classified into maximum, normal, and standby power. Several problems arise in the case of maximum power. Peak power is generated at the system power source in the maximum-power situation. Frequent generation of peak power can cause high-frequency problems and reduce the life of high-pressure parts (especially high-pressure capacitors). For example, when a plurality of PCs are used, system overload occurs due to peak power generation and causes problems, such as power failure and increase in electricity bills due to exceeded contract power. To solve this problem, a system peak power limit/compensation power circuit is proposed for a power supply under dynamic load profile conditions. The proposed circuit detects the system current to determine the power situation of the load. When the system current is higher than the set level, the circuit recognizes that the system current generates peak power and compensates for the load power through a converter using a super capacitor as the power source. Thus, the peak power of loads with a dynamic load profile is limited and compensated for, and problems, such as high-frequency issues, are solved. In addition, the life of high-pressure parts is increased.