• Journal of Power Electronics
• /
• 제19권1호
• /
• pp.44-57
• /
• 2019

Recently, the use of LLCL filters for grid inverters has been suggested to give better harmonic attenuation than the commonly used L and LCL filters, particularly around the switching frequency. Nevertheless, this filter is mainly designed for constant switching frequency pulse width modulation (CSF PWM) methods. In variable switching frequency PWM (VSF PWM), the harmonic components are distributed across a wide frequency band which complicates the use of a high order filter, including LCL and LLCL filters. Recently, a confined band variable switching frequency (CB-VSF) PWM method has been proposed and demonstrated to be superior to the conventional constant switching frequency (CSF) PWM in terms of switching losses. However, the applicability of LLCL filters for this type of CB-VSF PWM has not been discussed. In this paper, the authors study the suitability of an LLCL filter for CB-VSF PWM and propose design guidelines for the filter parameters. Using simulation and experimental results, it is demonstrated that the effectiveness of an LLCL filter with CB-VSF PWM depends on the parameters of the filters as well as the designed variable frequency band of the PWM. Simulation results confirm the performance of the suggested LLCL design, which is further validated using a lab scale prototype.

• 수도
• /
• 통권25호
• /
• pp.28-39
• /
• 1981

• 한국유체기계학회 논문집
• /
• 제16권1호
• /
• pp.11-16
• /
• 2013

A numerical study was conducted to improve the performance of an impeller of centrifugal compressor. Nine design variables were chosen with constraints. Only meridional contours and blade profile were adjusted. ANN (Artificial Neural Net) was adopted as a main optimization algorithm with PSO (Particle Swarm Optimization) in order to reduce the optimization time. At first, ANN was learned and trained with the design variable sets which were obtained using DOE (Design of Experiment). This ANN was continuously improved its accuracy for each generation of which population was one hundred. New design variable set in each generation was selected using a non-gradient based method of PSO in order to obtain the global optimized result. After $7^{th}$ generation, the prediction difference of efficiency and pressure ratio between ANN and CFD was less than 0.6%. From more than 1,200 design variable sets, a pareto of efficiency versus pressure ratio was obtained and an optimized result was selected based on the multi-objective function. On this optimized impeller, the efficiency and pressure ratio were improved by 1% and 9.3%, respectively.

• 한국기계가공학회지
• /
• 제16권5호
• /
• pp.126-133
• /
• 2017

This report investigates the stress distribution according to the location and shape change of the circular hole for the lightweight design of the cross beam of a railway passenger car and studies the lightweight design. To design a lightweight cross beam with a circular hole, we selected the non-circular crossbeam as a basic model, examined the stress distribution and displacement by position and determined the location, shape, size and quantity of the hole for light weight. We analyzed the effects of the position and shape of the hole on the maximum equivalent stress and displacement. The influencing factors were set as the design parameters, and the stress value was examined according to the variation of each variable. By considering the stress value according to the change of each variable and selecting the design parameter with the narrowest scattering value of the stress at each position of the hollow cross beam with various hole positions and shapes, we studied a cross beam with a circle hole under identical load condition to have an equal stress distribution to that of a non-circular cross beam.

• 한국의상디자인학회지
• /
• 제24권4호
• /
• pp.135-152
• /
• 2022

Recent weddings have been performed in more unique and characterful styles going beyond the existing same old method of past weddings, and they are changed into small weddings with simplified style without unnecessary procedures by choosing a wedding venue different from others. It is necessary to develop a new wedding dress design suitable for such changing wedding culture, and especially, dresses are required to have some practical designs, so that they can be worn not only for the wedding ceremony or party but also for everyday life. Therefore, the purpose of this study is to develop a new normal wedding dress for small weddings that reflect design according to the emerging small wedding culture. To this end, a theoretical review of small weddings was conducted, and based on this, a new normal wedding dress design was developed for small weddings. Based on practicality and economic feasibility, the New Normal Wedding Dress exhibited 'variable by wearing method' that changes according to the wearer's purpose and 'variable by attaching and detaching method' that changes according to the detachment of details. The small wedding dress developed through this study is expected to become a new standard for wedding dresses that is suitable for the changing wedding culture.

• 품질경영학회지
• /
• 제44권4호
• /
• pp.751-770
• /
• 2016

Purpose: Two-stage ${\bar{X}}$ chart is a useful tool for process control when a surrogate variable may be used together with a performance variable. This paper extends the two-stage ${\bar{X}}$ chart to a three stage version by decomposing the first stage into the preliminary stage and the main stage. Methods: The expected cost function is derived using Markov-chain approach. The optimal designs are found for numerical examples using a genetic algorithm combined with a pattern search algorithm and compared to those of the two-stage ${\bar{X}}$ chart. Sensitivity analysis is performed to see the parameter effects. Results: The proposed design outperforms the optimal design of the two-stage ${\bar{X}}$ chart in terms of the expected cost per unit time unless the correlation between the performance and surrogate variables is modest and the shift in process mean is smallish. Conclusion: Three-stage ${\bar{X}}$ chart may be a useful alternative to the two-stage ${\bar{X}}$ chart especially when the correlation between the performance and surrogate variables is relatively high and the shift in process mean is on the small side.

• 한국정밀공학회지
• /
• 제32권11호
• /
• pp.945-952
• /
• 2015

In drawing sheet metal, the blank holding force is applied to prevent wrinkling of the product and to add a tensile stress to the material for the plastic deformation. Applying an inappropriate blank holding force can cause wrinkling or fracture. Therefore, it is important to determine the appropriate blank holding force. Recent developments of the servo cushion open up the possibility to reduce the possibility of fracture and wrinkling by controlling the blank holding force along the stroke. In this study, a method is presented to find the optimal variable blank holding force curve, which uses statistical analysis with consideration of the nonlinear deformation path. The optimal blank holding force curve was numerically and experimentally applied to door inner parts. Consequently, it was shown that the application of the variable blank holding force curve to door inner parts could effectively reduce the possibility of fracture and wrinkling.

• International Journal of Automotive Technology
• /
• 제8권6호
• /
• pp.713-722
• /
• 2007

Design variables for suspension systems cannot always be realized in the actual suspension systems due to tolerances in manufacturing and assembly processes. In order to deal with these tolerances, design variables associated with kinematic configuration and compliance characteristics of suspensions are treated as random variables. The reliability of a design target with respect to a design variable is defined as the probability that the design target is in the acceptable design range for all possible values of the design variable. To compute reliability, the limit state, which is the boundary between the acceptable and unacceptable design, is expressed mathematically by a limit state function with value greater than 0 for acceptable design, and less than 0 for unacceptable design. Through reliability analysis, the acceptable range of design variables that satisfy a reliability target is specified. Furthermore, through sensitivity analysis, a general procedure for optimization of the design target with respect to the design variables has been established.

• 한국주거학회논문집
• /
• 제26권4호
• /
• pp.75-82
• /
• 2015

Although the government has revised the child welfare act, institutionalized the establishment of local children's centers, and given financial support for them, there are a number of problems with respect to their operation. Specifically, one of main problems is their limited space. Diverse problems that go with the arrangement of limited space and usability have occurred, however there are only a few strategies to use limited space flexibly. This study assumed variability as one of the methods to solve spatial problems. As a basic research for the assumption, Analyzing the variable method and characteristics of domestic and foreign child-care facility guidelines was performed trying to take advantage of as a basic data in order to seek a variable scheme of local children centers' indoor space. For this purpose, study analysed the methods and characteristics of variability centering on aspects related to variability which are environmental design elements required by local children's centers as suggested in previous studies. The results are as follows. First, the variability of space should be planned according to activity and time, and consider the methods of division, storage, and other facilities necessary. Second, methods of variability in space can be classified into creating areas and structures that are variable. Third, as a result of analysing the environmental design elements required by local children's centers, this study discovered the following characteristics: multi-purpose usability through a combination of variable devices, transition through a variable space medium and setting up areas and expansion of indoor variability assuming usability through internal and external connections.

• 대한기계학회논문집
• /
• 제15권6호
• /
• pp.2171-2180
• /
• 1991

본 연구에서는 구심터어빈의 설계시 많이 사용되고 있는 NASA의 안내깃 및 회 전익 손실모델들을 이용하여 PR과 K를 실험에 의존하지 않고 구하는 방법을 제시하고 자 한다. 그리고 이 방법을 가변 안내깃이 존재하거나 없는 가상의 구심터빈에 대하 여 탈설계 성능해석을 하여, 본 방법이 기존에 알려진 실험 현상과 유사한 경향을 보 이는지를 알아보기로 한다. 또한 안내깃이 있는 경우에 대하여 기존의 알려진 탈설 계 성능 예측용 프로그램과의 비교를 통하여 본 연구의 해석방법을 간접적으로 검증하 기로 한다.