• 전기학회논문지
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• 제59권1호
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• pp.1-8
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• 2010

The ultrafashionable machinery that require high quality electricity power has been daily come into being. Because domestic power system has been larger and more complicated in accordance with raising power demand by power market requirement. Because of these power market situations, The FACTS (Flexible AC Transmission System) which is power transmission system for the next generation to meet flexible supply the power and reliability has been applied. If they, compensators and FACTS, are used inter-efficiently in range that does not affect the stability and a badly influence the security, they might be increase in the voltage stability of system, supply reliability and also achieve the voltage control in a suddenly changed power system. Therefore we describe and suggest on this treatise that a plan for coordination control between UPFC, Shunt elements (Sh. Capacitors & Sh. Reactors) among compensators and also describe the method to keep or control the voltage of power system in allowable ranges. The method follows that, we used characteristics of each equipment, UPFC would be also settled to keep the identified voltage range in change of load bus, Shunt elements also would be settled to supply the reactive power shortage in out of operating range of UPFC to cope actively with change of the power system. As the result of simulation, it is possible to keep the load bus voltage in limited range in spite of broad load range condition. This helps greatly for the improvements of supply reliability and voltage stability.

• KDI Journal of Economic Policy
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• 제37권1호
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• pp.19-44
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• 2015

This paper examines the effect of the global financial crisis on corporate investment in Korea. Specifically, the crisis was considered to have possibly constrained firm-level investment as the negative shock to the credit supply dramatically unfolded. As Duchin et al. (2010) demonstrated, if a negative supply-side shock is evident during a crisis period, larger cash holdings before the crisis will lead to fewer constraints to corporate investment, or vice versa. In order to investigate the supply-side effect of the crisis, we use firm-level financial data, including firms listed on the Korean stock market as well as small and medium-sized enterprises. We find that corporate investment declined significantly after the crisis, even if we control for factors associated with the demand side, such as contemporaneous capital productivity and cash flow. More importantly, the decline is positively and significantly related to cash holdings before the crisis, implying the negative effect of a credit supply shock. Small and medium enterprises experienced relatively sharp investment declines compared to those of larger firms, and the relationship between pre-crisis cash amounts and the degree of investment decline is greater than that in large firms. Additionally, we examine whether the negative effect persists up to the present, finding evidence that the cash-investment relationship continues in small and medium-sized enterprises.

• 한국산업융합학회 논문집
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• 제25권6_2호
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• pp.1071-1081
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• 2022

As the demand for high-rise buildings increases, the demand for high-speed elevators is also increasing. In order to make a high-speed elevator, a method is needed to reduce the weight of the elevator's components, which is a constraint on the increase in speed. As a measure to reduce the weight, it is possible to remove the traveling cable for power and signal supply. Since the weight of the traveling cable varies depending on the position of the carriage, it is difficult to compensate the weight using the counter weight. The power supply is a structure in which a brush-rail type power input terminal is installed in the elevator hoistway to receive power in a contact-type manner while the carriage is moving. If a small-capacity ESS is installed in a passenger car, power can be supplied uninterruptedly inside the passenger car. A small-capacity ESS charging system to be applied to such an elevator system is required to perform several functions. First, the passenger Car must be able to charge as much as possible even during high-speed operation. A control algorithm with high responsiveness is required because charging starts and ends repeatedly by the partially installed input power stage. In addition, if the input-side line impedance is large due to the structure of the system and the response characteristic is increased, the stability of the system may be lowered. Accordingly, in this paper, we propose a control algorithm that has a stable steady-state output while having a fast response in a transient state. To verify the proposed control algorithm, simulation was conducted using PSIM, and the performance of the controller was verified by manufacturing a prototype buck conveter charger.

• 한국항공운항학회지
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• 제17권3호
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• pp.32-39
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• 2009

Due to the lack of navigable airspace caused by worldwide air traffic increases, air traffic control(ATC) services are becoming more complex, which results in the increase of aircraft accidents. To cope with these challenges, major aviation institutes abroad are actively conducting research regarding the human factors affecting controllers but as of late, no such specialized activities have been found in Korea. Due to the dynamic attributes of ATC operations, management of controller's situation awareness(SA) and workload, and knowledge on the impact of abnormal aircraft to controllers are very important. Furthermore, using actual flight data of each country will lead to valuable results, because individually, it has different airspace characteristics and air traffic volumes. This study assumed that air traffic difficulties would affect the controller's SA and workload. To testify the above hypothesis, the abnormal air traffic situations are simulated by using ATC simulator. The findings indicated that the effect of traffic situations containing abnormal aircraft on the controller's SA and workload, it led to demand increase and supply decrease in SA, and increased mental demand, temporal demand, effort and mean workload score in the workload.

• 상하수도학회지
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• 제11권1호
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• pp.109-118
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• 1997

In this study, we examined the structural analysis of water demand fluctuation for water distribution control of water supply network. In order to analyze for the length of stationary time series, we calculate autocorrelation coefficient of each case equally divided data size. As a result, it was found that, with the data size of around three months, any case could be used as stationary time series. we analyze cross-correlation coefficient between the daily water consumption's data and primary influence factors. As a result, we have decided to use weather conditions and maximum temperature as natural primary factors and holidays as a social factor. Applying the multiple ARIMA model, we obtains an effective model to describe the daily water demand prediction. From the forecasting result, even though we forecast water distribution quantity of the following year, estimated values well express the flctuations of measurements. Thus, the suitability of the model for practical use can be confirmed. When this model is used for practical water distribution control, water distribution quantity for the following day should be found by inputting maximum temperature and weather conditions obtained from weather forecast, and water purification plants and service reservoirs should be operated based on this information while operation of pumps and valves should be set up. Consequently, we will be able to devise a rational water management system.

• 한국농공학회논문집
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• 제48권3호
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• pp.35-45
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• 2006

Fallow paddy areas have been increased due to the import of cheap agricultural product, and the unbalance between farming cost and rice price since 1990. In domestic, rice production control that decrease paddy field area has been introduced for the control of rice demand and supply and stabilization of rice price since 2003. Because of the desire of paddy field's owner to create benefit by using paddy for other object, fallow paddy would be continuously increased. In the other aspect, many people in the world is suffering from hunger because of the shortage of food. In case of Korea, continuous drought and flood damages will be potential concern of stable food supply. From this viewpoint, the increasing fallow paddy area needs to be protected from the devastation by weed breeding for the re-cultivation. In this study, fallow paddy managed with the shallow pools and shallows was selected fur monitoring and analyzing of water quality and plant body change. As the results, the managed fallow paddy found to be effective in the purification of water quality and the control of plant growth.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1992년도 한국자동제어학술회의논문집(국제학술편); KOEX, Seoul; 19-21 Oct. 1992
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• pp.106-111
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• 1992

In order to achieve stable and efficient use of energy at iron and steel works, a model for the prediction of supply and demand of electric power system is developed on the basis of the information on operation and particular patterns of electric power consumption. The optimal amount of electric power to be purchased and the optimal fuel allocation for the in-house electric power plants are also obtained by a mixed-integer linear programming(MILP) and a nonlinear programming (NLP) solutions, respectively. The validity and the effectiveness of the proposed model are investigated by several illustrative examples. The simulation results show the satisfactory energy saving by the optimal solution obtained through this research.

• 한국가금학회지
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• 제47권1호
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• pp.39-48
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• 2020

The present study intended to analyze and detect any possible shortcomings in the current egg distribution system in Korea through a questionnaire. The institutional system and cases of operation thereof in advanced countries such as the USA, Japan, and Germany for the development of the egg distribution industry in Korea. The results revealed the following issues: absent pricing system, ineffective egg distribution, and difficulty in balancing supply and demand. Suggestions for addressing these issues and the subsequent improvement were based on cases found in the instated systems of advanced countries, and were given as follows: (i) The existing GP Center needs to be separated from the farms of laying hens, and the current institutional system and its operations need to be improved and should be approved by the government. Parallel to the institutional improvement, establishing a distribution system centered on the GP Center would be desirable. (ii) Egg pricing regulations are needed as a standard to determine the price of eggs. (iii) The reinforcing control standards and securing means for egg preservation are pertinent to each stage of egg distribution and should take into account environmental factors such as egg preservation temperature to guarantee high hygiene standards and egg safety.

• 한국식생활문화학회지
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• 제32권4호
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• pp.303-310
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• 2017

Kimchi cabbage is in demand all year, but there is an unbalance in its supply and demand due to climate reasons, requiring practical methods for extending storage without high cost. Therefore, this study aimed to assess available storage methods. 'Choongwang' Kimchi cabbages cultivated in Pyeongchang, Gangwon-do were on June 14 harvested and packed in plastic boxes. Control group was treated by loading four to five heads. Moisturized paper was applied as a liner inside the box to prevent dehumidification and damage to the cut root parts, and a small loading amount (three heads) was applied for better air circulation. Weight loss rates after 12 weeks of storage were 13.83% in the control group, 12.57% in the first group, and 13.38% in the second group. Trimming loss rates after 9 weeks of storage were 14.96% in the control group, 12.29% in the first group, and 12.55% in the second group. As a result of the sensory test, the control group lost its marketability after 6 weeks of storage, while the second group maintained it until 9 weeks and the first group maintained it until 12 weeks and scored higher than 6 points. Therefore, the tested methods were effective for extending the freshness of Kimchi.

• KIEAE Journal
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• 제17권3호
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• pp.133-140
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• 2017

Purpose: The construction of New Han-ok style public buildings is a construction that can not be seen in traditional Han-ok, and it is a construction that combines traditional wooden structure, RC structure, and steel structure. Therefore, construction different from general construction is complicated and complex. It is necessary to accurately understand the construction method of each field rather than the general construction management method and study the method suitable for New Han-ok style public buildings. Also, since the New Han-ok style public building business is the first business to be introduced in Korea, new process management is needed rather than general process management. Method: The research method is as follows. Analyze process management through theoretical considerations and analyze the differences from general construction projects. Next, we want to identify the characteristics and problems of the process control method applied to real cases. Finally, the results of this analysis suggest ways to improve process management. Result: Therefore, it is necessary to establish a precise plan from the basic design to the construction of the public building construction management. In addition, careful planning should be made so that the supply and demand of materials and the supply and demand of personnel can be achieved smoothly.