• Journal of Electrical Engineering and Technology
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• v.12 no.5
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• pp.1925-1933
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• 2017

The brushless DC motor's commutation torque ripple is caused by inconsistency in the rate of phase current change. Thus, a method that considers armature resistance is proposed to modulate phase current. The three-phase control strategy, which involves the "open-phase conduction, off-phase pulse width modulation, and maintained non-commutation phase" technique, is applied during commutation at full-speed segments of the motor. Changes in each phase current are analyzed theoretically by establishing mathematical model based on phase current to determine the relative difference among shutdown phase, duty, and motor operating parameters. The turn-on and turn-off phase current change rates are made to be consistent to ensure less non-commutation phase current ripple, then the torque ripple is inhibited. The simulation results show that the phase commutation current and torque ripple coefficient of the proposed method are reduced from 56.9% and 55.5% to 6.8% and 6.1%, respectively. In the experiment system, the pulsation coefficient of the motor phase current is reduced from 40.0% to 16.7% at low speed and 50.0% to 18.8% at high speed. The simulation and experimental results show that the proposed control method significantly inhibits commutation current and torque in the full section.

• Proceedings of the KIEE Conference
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• 1995.07a
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• pp.247-250
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• 1995

This paper proposes a new method to reduce the torque ripple in vector controlled inverter fed synchronous motor systems. In three phase voltage source inverter systems, all the three line currents are generally not measured and the currents of two lines are measured through two sensors and two A/D converters. The measured currents may contain some error due to the non-ideality of the current sensors and A/D converters, and the error coefficient of two line currents are not same. As a result, the developed torque contains the torque ripple. The proposed method can eliminate the torque ripple by setting the error coefficient to same value. To verify the proposed method, digital simulations are carried out.

• Journal of the Korean Solar Energy Society
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• v.39 no.2
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• pp.81-92
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• 2019

When Photovoltaic inverter is connected to grid and used as PVPCS (Photovoltaic Power Conditioning System), 120 Hz AC ripple occurs at the dc-link capacitor voltage. This AC ripple reduces the efficiency of PVPCS and shortens the lifetime of the capacitor. In this paper, we design a notch filter to remove AC ripple. As a result, the AC voltage ripple was removed from the dc link and the THD of the PVPCS output current with the notch filter was lowered. This notch filter is determined by the damping coefficient, the bandwidth coefficient, and the switching frequency. Among these, the switching frequency determines the switching loss and the size of the LC filter, and the PVPCS with the high switching frequency has a greater efficiency loss due to the switching loss than the efficiency improvement by the notch filter. Therefore, it is important to set the optimum switching frequency in the PVPCS with the notch filter applied. In this paper, THD and switching loss of PVPCS output current with notch filter are calculated through simulation, and cost function to calculate optimum switching frequency through data is proposed.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2018.10a
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• pp.470-473
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• 2018

Using High-order Modulation in wideband system is sensitive to change of wireless channel environment as well as changes in ripple characteristics that can occur when baseband signals pass through RF equipment. Therefore, it is necessary to design and RF tuning that minimizes ripple characteristics change, which is difficult to implement systematically and takes a long time. In this paper, we analyze the fixed ripple characteristics of the baseband signal distored through the RF transmitting and receiving equipment. And the function of compensating the compensation filter by the modem receiver is implemented in 256 TCM. Also, it is confirmed that SNR and received sensitivity are improved by applying a digital compensation filter in a channel with poor RF equipment ripple characteristics.

• Transactions of the Korean Society of Automotive Engineers
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• v.11 no.3
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• pp.106-114
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• 2003

The pressure ripple in the delivery port is caused by flow ripple, which is induced by variation of pumping chamber volume. The other reason is the reverse flow from the outlet volume produced by pressure difference between pumping chamber and outlet volume, when the pumping chamber is connected with the outlet volume. In this study, a mathematical model is presented for analyzing discharge pressure ripple, which includes vane detachment, cam ring movement , and fluid inertia effects in V-groove in the side plate. From the analysis and experiment, it was found that V-groove on the side plate, coefficient of spring supporting the cam ring, and average discharge pressure are the main factors of discharge pressure ripple in variable displacement vane pump. The theoretical results, provided in this study, were well agreed with experimental results. The analytical model to estimate the magnitude of pressure ripple in this study is expected to be used f3r the optimal design of the variable displacement vane pump.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.2 no.4
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• pp.316-326
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• 1990

The measurements of heat transfer and pressure drop were performed on ripple tube with air flow. The results with the tube were compared with the performance of smooth tube. The enhancements in heat transfer coefficient for ripple tube, being compared with smooth tube, was ranged from 7.4 to 39 percent. The local Nusselt number for the inner fin tube, being compared with that for smooth tube, varied from 7.4% to 39%, while the corresponding increase in friction factors were 4.1 to 8.1%. One of the most direct indications of Nusselt number of ripple tube is given as following equation: $$Nu=0.061Re^{0.75}Pr^{0.4}(Tb/Tw)^{0.5}$$ We can see that Nusselt number for ripple tube in this experiment is consistent with the theoretical one taken from Walkinson's equation at Reynolds number range from 8,000 to 20,000.

• Land and Housing Review
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• v.11 no.4
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• pp.15-26
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• 2020

This study analyzes the Domestic Economic Ripple Effect (DERE) of the Donghae-Bukpuseon Railway (DBR). Input-Output Analysis and Scenario Analysis are employed. First, the future demand is approximately 6.86 billion people, 1.4 billion tons of logistics, and future forecast production is 1.2 trillion won for passengers, and 0.15 trillion won for logistics. Second, the production inducement (PI) coefficient of the railway industry is 2.080, the value-added inducement (VAI) coefficient is 0.680, the import inducement (II) coefficient is 0.32 and the employment inducement (EI) coefficient is 6.45. Third, for the DERE, PI is 2.846 trillion won, VAI is 0.939 trillion won, II is 0.446 trillion won, and EI is 8,737 people/1 billion won. Fourth, PI is approximately 2.8 trillion won, and the payback period is 35 years. Scenario 1 (a 50% increase in the demand for tourism) takes approximately 27 years, Scenario 2 (an 100% increase), 20 years, and Scenario3 (an 150% increase), 16 years. The successful way of the DBR is to enlarge the linkage effect of trans-railways for which international cooperation and agreements are needed. Also, even if the DBR is isolated due to worsening inter-Korea relations, the development of tourism resources is important for public investment feasibility.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.5 no.3
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• pp.240-249
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• 1993

The suspended sediment mechanism was systematically investigated by analyzing existing data together with new data obtained under several wave folds. A simple empirical formula has been developed to predict the time-averaged suspended sediment concentration above movable bed by the effect of wave and current interaction. The present study shows linear dependency of the diffusion coefficient of suspended sediment on the eddy viscosity coefficient obtained by considering the ripple geometry. Furthermore, it is proved that reference sediment concentration is reduced by the effect of ripple asymmetry.

• The Journal of the Korea Contents Association
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• v.21 no.9
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• pp.299-311
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• 2021

The purpose of this study is to analyze the ripple effect of the Chinese education industry on the national economy by using the industry-related table of 2017 by the China Statistical Office to use it as policy data for revitalization of the Chinese education industry in the future. To achieve this purpose, 149 industries in the basic classification of the industry-related table were classified into 32 industries. Based on these classifications, by analyzing the production induction coefficient, sensitivity coefficient, influence coefficient, yield inducement coefficient, production tax induction coefficient, and labor induction coefficient, etc. The purpose of this study is to understand the relationship between different industries and to find out the economic impact of the Chinese education industry. The analysis results show that in 2017, the total production induction coefficient of China's education industry was 1.7188, the row total was 1.0626, the sensitivity coefficient was 0.01211, the influence coefficient was 0.01958, the income induction coefficient was 0.6667, the production tax induction coefficient was 0.035, and the final demand was 1 billion yuan. When this occurs, the labor induction coefficient shows a total of 31,254 persons (indirect 15,541 persons, direct 15,713 persons). Based on the analysis results, this study suggested the implications that government support, technology introduction and application of new operating models, policy regulations, and efficient supervision of the system and president are required for further development of the Chinese education industry.

• Journal of Information Science Theory and Practice
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• v.10 no.spc
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• pp.66-75
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• 2022

The manufacturing industry is the foundation that drives economic growth, and manufacturing innovation is essential for sustainable growth advantage and the transition into a digital economy. Therefore, major countries actively support the field of simulations, which incorporate information and communication technologies into manufacturing, and announce various policies at the national level along with increasing investment. Simulation technology virtualizes product development processes to replace physical production and experimentation of products, dramatically reducing time and costs. In South Korea, the Korea Institute of Science and Technology Information (KISTI) has supported manufacturing companies for about 14 years by providing relevant technologies. This study uses the input-output table for the Bank of Korea to analyze the economic ripple effect. First, we identified the domestic industrial sector dealing with the supercomputing-based simulation industry. Then we analyzed its ripple effects by dividing them into the production inducement effect, value-added inducement effect, employment inducement effect, and forward/backward linkage effect. Consequently, when the supercomputing simulation budget of KISTI (28.3 billion won, 2007-2020) was set as an input coefficient, the analysis showed 45.1 billion won as the production inducement effect, 24.7 billion won as the value-added inducement effect, and 282 individuals per 1 billion won as the employment inducement effect. This study is significant in that it derived the effects of the inputs by analyzing the economic ripple effects of the projects of KISTI, which have been supporting South Korean manufacturing companies for the past 14 years with supercomputing-based simulations.