• Transactions of the Korean Society of Automotive Engineers
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• v.8 no.5
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• pp.114-120
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• 2000

Friction forces of piston rings for a typical SI engine were independently measured while excluding the effects of cylinder pressure, oil starvation and piston secondary motion using a floating liner system. Friction patterns, represented by the measured friction forces, were classified into five frictional modes with regard to the combination of predominant lubrication regimes(boundary, mixed and hydrodynamic lubrication) and stroke regions(mid-stroke and dead centers). The modes were identified on the Stribeck diagram of the dimensionless bearing parameter and friction coefficients which were evaluated at the mid-stroke and at the dead centers. And the frictional modes were estimated to the full operation range. The compression rings behave in the mode where hydrodynamic lubrication is dominant at the mid-stroke and mixed lubrication is dominant at the dead centers under steady operating conditions. However, the oil control ring behave in the mode where mixed lubrication is dominant throughout the entire stroke.

• Journal of the Korean Society of Systems Engineering
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• v.1 no.2
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• pp.43-48
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• 2005

This paper describes the results of applying States and Modes Analysis, one of the requirements analysis techniques, to the development requirements of flight control software for Smart UAV. State/mode table enabled us to investigate various operation and design concepts, and as a result essential requirements for flight control software were established without omitting necessary requirements. Through the use of scenario-specific state transition diagrams, dynamic behaviours and control/response interfaces between each state and mode could been clearly identified, which made it possible to establish requirements related to dynamic behaviours of states and modes which are essential to the design of flight control software.

• Journal of Korea Foundry Society
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• v.24 no.5
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• pp.273-280
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• 2004

Vibrational motions of the compaction table were investigated to select the optimal operation conditions of sand filling and compaction for the EPC process. Their modes were measured at the nine points of the table with changing the relative rotation angles between the two eccentric mass vibrators which were attached parallel beneath the table. Well-defined vibration modes were measured at the center of the table but those of left and right sides of the table were distorted regardless of rotational angle differences. The distortion of vibration modes at both sides of the table were caused by the moment generated by offset positions of two eccentric masses. It was found that the uniform vibration modes would be gathered by controlling the relative distances between the rotating axis and the center of gravity in the compaction system at the various conditions of vibration modes and rotational angle differences.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.16 no.4
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• pp.771-777
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• 2012

This paper proposes a binary arithmetic encoder of CABAC using a Common Operation Unit including the three modes. The binary arithmetic encoder performing arithmetic encoding and renormalizer can be simply implemented into a hardware architecture since the COU is used regardless of the modes. The proposed binary arithmetic encoder of CABAC includes Context RAM, Context Updater, Common Operation Unit and Bit-Gen. The architecture consists of 4-stage pipeline operating one symbol for each clock cycle. The area of proposed binary arithmetic encoder of CABAC is reduced up to 47%, the performance of proposed binary arithmetic encoder of CABAC is 19% higher than the previous architecture.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.3 s.246
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• pp.193-200
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• 2006

The purpose of this study is to compare the part-load performance of a SOFC/GT hybrid power system with three different kinds of load-following operation modes. The primary mode for the part load operation of a hybrid power system is the reduction of supplied fuel (e.g., fuel control mode) to the hybrid system. The other two options, i.e., variable speed and VIGV controls, are related to the reduction of supplied air simultaneously with the reduction of supplied fuel to the system. With the performance analysis of a SOFC/GT hybrid power system, it is concluded that the variable speed con佐ol mode Provides the best performance for the part-load operations. It is also found that the VIGV control mode, with its better performance behavior than the fuel control mode, can be used as an important option for the part-load operation especially in case that the variable speed control mode can not be adopted.

• Journal of IKEEE
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• v.25 no.1
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• pp.218-228
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• 2021

This paper presents the high-efficiency DC-DC converter using the multi-resonant-circuit. The proposed converter has the power topology of half-bridge and utilizes the multi-resonant-circuit that is composed of 2 inductors (LL) and 1 capacitor (C) to achieve high-efficiency. The multi-resonant-circuit forms each resonant circuit of series circuit type with each resonant frequency, according to the operation modes. This paper first describes the operation pirinciples of proposed converter by the operation modes and steady-state fundamental approximation modelling. Then it shows a design example of the proposed converter based on the principles. And it is validated that the proposed converter has the operation characteristics of high-efficiency DC-DC power conversion through the experimental results of prototype converter implemented by the designed circuit parameters.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.67 no.2
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• pp.224-232
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• 2018

According to government policy, renewable energy facility such as solar power generation is being implemented for newly constructed buildings. In recent years, the introduction of Energy Storage System (ESS) served as an emergency power for replacing an existing diesel generator has been increasing. Furthermore, in order to expand the efficacy of the ESS operation, operation in combination with renewable energy sources such as solar and wind power generation is increasing. Hence, development of the ESS operation algorithms for emergency mode as well as the peak power cut mode, which is the essential feature of ESS, are necessary. The operational scenarios of ESS need to consider load power requirement and the amount of the power generation by renewable energy sources. For the verification of the developed scenarios, tests under the actual situation are demanded, but there is a difficulty in simulating the emergency operation situation such as system failure in the actual site. Therefore, this paper proposes simulation models for the HILS(Hardware In the Loop Simulation) and operation modes developed through HILS for the ESS operated with renewable energy source under peak power reduction and emergency modes. The paper shows that the ESS operation scenarios developed through HILS work properly at the actual site, and it verifies the effectiveness of the control logic developed by the HILS.

• Journal of Energy Engineering
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• v.18 no.1
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• pp.37-48
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• 2009

Recently, the significance of Green-Energy led by low-carbon Green-Development is increasing as well in Korea. Among them, the most practical solution is the cogeneration which performs the best energy efficiency. This paper addresses the two of RCS(Regional Cogeneration System) connecting heat each other. It is conducted to quantitatively evaluate algorithm that optimally operate the heat transaction considering various operating modes. The proposed method is tested using the real system. Through the case studies, it is verified that the proposed algorithm of heat transaction can evaluate availability.

• Journal of Power Electronics
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• v.17 no.3
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• pp.744-755
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• 2017

With the high penetration of various sustainable energy sources, the control and protection of Microgrids has become a challenging problem considering the inherent current limitation feature of inverter-based Distributed Generators (DGs) and the bidirectional power flow in Microgrids. In this paper, a hybrid control and protection scheme is proposed, which combines the traditional inverse-time overcurrent protection with the biased differential protection for different feeders with different kinds of loads. It naturally accommodates various control strategies such as P-Q control and V-f control. The parameter settings of the protection scheme are analyzed and calculated through a fast Fourier transform algorithm, and the stability of the control strategy is discussed by building a small signal model in MATLAB. Different operation modes such as the grid-connected mode, the islanding mode, and the transitions between these two modes are ensured. A Microgrid model is established in PSCAD and the analysis results show that a Microgrid system can be effectively protected against different faults such as the single phase to ground and the three phase faults in both the grid-connected and islanded operation modes.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.64 no.11
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• pp.1618-1625
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• 2015

The reliability of catenary system is very important for uninterrupted train operation as it supplies electric power to train without redundant facilities. This paper provides a systematic approach to the reliability analysis of the catenary system based on FMECA procedures defined by global standards such as MIL Std 1692a and IEC 60812. Field failure data collected from the operation and maintenance of high-speed railway catenary system for 9 years are used to derive critical failure modes and to evaluate the criticality of the failure modes. Evaluation of the criticality are carried out by quantitative procedures defined by MIL Std 1692a and by criticality matrix defined by IEC 60812. FMECA results suggests that three critical failure modes should be checked carefully during maintenance work, which include strand break of dropper and voltage equalizing wire, power supply failure of feeder. Maintenance procedure of catenary system in order of importance is suggested too. These results can be applied to maintenance planning and design of catenary system to improve the reliability of electric railway system.