Impedance Modeling and Stability Mechanism Analysis for Grid Forming and Grid Following Converters

Zhu Zuobin,Sun Shumin,Li Zhenxing,Huang Shaoping 대한전기학회 2024 Journal of Electrical Engineering & Technology Vol.19 No.5

When diff erent types of converters exist in a local area, the use of diff erent control methods between converters may bring about system instability, which will lead to the inability of distributed power supply to operate normally. it is important to propose a stability analysis method for diff erent types of shunt converters. Existing impedance models are less studied for modeling and stability mechanism analysis of hybrid converter operation modes of diff erent control Hence, a generalized virtual synchronous generator (VSG) impedance model and stability mechanism analysis method is proposed. Firstly, a generalized VSG impedance model is established and a stability mechanism analysis is performed. Secondly, external stability analysis and internal stability analysis on the system are conducted. Finally, a simulation model and an experimental platform for diff erent control converters is respectively established for verifi cation stability analysis theory. The stability mechanism analysis of converter grid connection lays a theoretical foundation for providing stable and reliable interfaces for large-scale new energy integration into the power grid. To suppress the resonance problem caused by the increase of the number of grid-following VSGs, a virtual conductor is introduced into parallel system to improve system’s stability. After introduced virtual conductor, output current waveform is smooth, and the harmonic content is reduced from 12.3 to 2.4%, compared with unimproved method.

현장 모니터링 결과를 이용한 광미 적치사면 안정성의 수치해석적 연구

송영석 ( Young-suk Song ) 대한지질공학회 2017 지질공학 Vol.27 No.1

광미 적치사면에서 측정된 모니터링 결과와 현장조건을 고려한 수치해석결과를 이용하여 강우시 불포화 토층내 모관흡수력 변화를 비교하고 이를 토대로 사면안정해석을 수행하였다. 이를 위하여 계측기간 동안 강우강도가 가장 크게 발생된 기간(72시간)을 선정하고, 대상기간 동안의 모관흡수력과 강우자료를 분석하였다. 그리고 현장에서 측정된 강우자료를 적용하여 침투 및 사면안정해석을 수행하였다. 강우에 따른 사면내 침투거동을 해석하기 위하여 SEEP/W를 활용하고 사면내 침투깊이를 고려한 사면안정해석을 위하여 SLOPE/W를 활용하였다. 먼저 현장에서 측정된 강우자료를 적용하여 SEEP/W를 이용한 침투해석을 수행하였다. 침투해석으로 계산된 모관흡수력과 현장계측으로 측정된 모관흡수력을 비교한 결과 모관흡수력의 크기에서는 다소 차이가 있으나 시간에 따른 변화양상은 유사한 것으로 나타났다. 그리고 침투해석결과와 연동하여 SLOPE/W를 이용한 사면안정해석을 수행한 결과 강우강도가 급속하게 증가되는 시점에서 사면안전율은 크게 감소하였으며, 이후 강우가 발생되지 않는 경우 사면안전율이 회복되는 것으로 해석되었다. Variations in matric suction were compared between field measurements and numerical analysis for a tailings dump slope. We performed an analysis of slope stability using precipitation records measured in the field, selecting the period (72 hours) of highest rainfall intensity during the field monitoring, for which the matric suction and rainfall records measured in the field were analyzed. In addition, we applied the precipitation records of this period to the numerical analysis. SEEP/W and SLOPE/W were used to analyze the seepage flow in the slope due to rainfall and to investigate the slope stability considering the wetting front depth from the ground surface, respectively. The seepage analysis, using SEEP/W, was carried out on the rainfall data obtained in the field. Comparisons between the field monitoring data and simulation results for matric suction show some quantitative difference but similar patterns of temporal variation. According to the results of slope stability analysis using SLOPE/W and the results of seepage analysis, the safety factor of the slope showed a sudden increase at the point of rapid increase in rainfall intensity. It then recovered because subsequent rainfall was scarce. Therefore, the stability of the tailings dump slope can be reasonably estimated if seepage and slope stability analyses, based on precipitation records, have been carried out.

Structural Stability of Cable-stayed Bridges

김승준,원덕희,이기세,강영종 한국강구조학회 2015 International Journal of Steel Structures Vol.15 No.3

This paper presents an investigation of the structural stability of cable-stayed bridges based on nonlinear analysis. In general, girders and masts of cable-stayed bridges are always subjected to compressive forces due to pre-tensioned stay cables. Cablestayed bridges exhibit various geometric nonlinearities, such as the cable-sag effect, beam-column effect of girders and masts, and large displacement effect. In this study, the characteristics of the structural stability of cable-stayed bridges are investigated. Because of various geometric nonlinearities, nonlinear finite element analysis should be performed for stability analysis instead of conventional eigenvalue analysis. Furthermore, the initial shape analysis should be performed prior to live load analysis in order to consider the dead load condition rationally. A two-step analysis method, developed based on the theory of nonlinear finite element method, is presented in this study for stability analysis under live load cases. An intensive series of parametric studies is subsequently performed using three-span cable-stayed bridges. The main buckling modes are classified depending on the location of the critical members. Also, the effects of cable arrangement, girder-mast stiffness ratio, area, and the number of cables on the structural stability are extensively investigated.

토사 절토사면 안정성 영향인자의 민감도 분석

유남재,박병수,전상현,조한기 강원대학교 산업기술연구소 2006 産業技術硏究 Vol.26 No.B

A sensitivity analysis about effects of influencing factors on the stability of Soil cut slope was performed. Slope stability analyses were carried out under dry, rainy and seismic conditions. Dominant factors controlling the slope stability were chosen such as cohesion and internal friction angle, unit weight of soil, water table and seismic horizontal coefficient used for the slope stability during eurthquake. Parametric stability analysis with those factors was performed for sensitivity analysis. As results of analyzing the sensitivity of factors under dry and rainy conditions, effects of cohesion, internal friction angle and unit weight of soil on the stability of slope are more critical in the dry condition than in the rainy condition. Cohesion and internal friction angle are more dominant factors influencing the slope stability irrespective of dry or rainy conditions than unit weight of soil and the horizontal seismic coefficient. The unit weight and the horizontal seismic coefficient affects crucially the stability according to conditions of slope formation and dry or rainy seasons. For the effect of horizontal seismic coefficient on stability of slope, safety factor of slope is not affected significantly by dry or rainy conditions, However, increase of the horizontal seismic coefficient under the rainy condition does reduce the safety factor significantly rather than the dry condition. Therefore, it is needed that the location of the water table is assigned appropriately to satisfy the required safety factor of stability in the case of checking slope stability for the rainy and seismic conditions.

이종지질 분포사면에서의 3차원 사면안정해석

서용석 ( Yong Seok Seo ),이경미 ( Kyoung Mi Lee ),김광염 ( Kwang Yeom Kim ) 대한지질공학회 2011 지질공학 Vol.21 No.1

화강암과 안산암질 암맥이 공존하고 있는 붕괴사면을 대상으로 지질에 의한 전단강도의 차이를 반영한 3차원 사면안정해석을 수행하였다. 지질이 서로 다른 두 종류의 파괴면에 대한 전단강도를 파악하기 위하여 흙-암 경계면 직접전단시험을 수행하였고, 또한 상부 풍화토층에 대한 실내토질시험을 실시하였다. 시험결과 풍화토층에 비하여 흙-암 경계면의 전단강도가 낮게 나타났다. 사면내 지질분포의 차이가 안정성해석 결과에 영향을 주는 것을 알아보기 위하여 한계평형법을 이용한 2차원사면안정성 해석을 대표단면에서 실시하였으며, 사면내 분포지질에 따라 입력치를 다르게 할 수 있는 3차원사면안정성해석을 실시하여 2차원안정성해석과 그 결과를 비교하였다. 해석결과에 의하면 안전율이 건기시 0.92와 포화시 0.32로 모두 불안정하게 나타난 2차원해석결과와는 달리 3차원해석결과에서는 건기시에 안전율이 1.26, 포화시에 0.55로 나타났다. 이러한 결과는 사면내 지질분포를 고려할 경우 안정성 해석의 결과가 달라질 수 있음을 보여주고 있으며, 우기 직후 붕괴가 일어났던 점을 고려하면 3차원해석결과가 보다 현실적인 것으로 판단된다. Three-dimensional slope stability analysis was applied to a failed dual-lithology slope containing both granite and an andesitic dyke, taking account of the differences in shear strength of the different lithologies. A direct shear test of the soil-rock boundary was performed to examine the shear strength of two different types of failure surfaces within different lithologies, and a laboratory test was performed on an upper, weathered soil layer. The test results indicate that shear strength was lower at the soil-rock boundary than within the weathered soil layer. A representative geological section was subjected to two-dimensional slope stability analysis using a limit equilibrium method to assess whether the distribution of lithologies upon the slope influences the results of stability analysis. The results were then compared with those of three-dimensional slope stability analysis, for which input parameters can be varied according to the distribution of lithologies upon the slope. The three-dimensional analysis yielded safety factors of 1.26 under dry conditions and 0.55 under wet conditions, whereas the two-dimensional analysis yielded unstable safety factors of 0.92 and 0.32, respectively. These findings show that the results of stability analysis are affected by the distribution of different lithologies upon the slope. Given that the studied slope collapsed immediately after rainfall, it is likely that the results of the three-dimensional analysis are more reliable.

역학적으로 엄밀한 사면안정도표의 제안

김종민 한국지반공학회 2004 한국지반공학회논문집 Vol.20 No.1

In this study, a slope stability chart for assessing stability of homogeneous simple soil slopes is proposed. Most existing slope stability charts are based on limit equilibrium method, which is not rigorous in mechanical standpoint. Meanwhile, limit analysis based on the principle of virtual work and the bound theorems of plasticity is suitable for evaluating the stability of geotechnical structures such as slope due to its simplicity in computation and mechanical rigor. Numerical limit analysis taking advantage of finite elements and linear programming can consider various slope conditions and, in addition, find the optimum stability solution with effeciency. In this study, a numerical limit analysis program in terms of effective stress is developed and a mechanically rigorous slope stability chart is proposed by performing stability analyses for various slope conditions. Pore pressure ratio, commonly used in stability charts, is applied to consider the effects of pore pressure for effective stress analysis. As a result of comparison between proposed stability chart and Spencer's stability chart, it was found that Spencer's chart solutions are biased to lower bound which means conservative in design.

SCP 시공지반의 성토사면 안정해석법 비교

안준상,김병일,박용원 明知大學校 産業技術硏究所 1999 産業技術硏究所論文集 Vol.18 No.-

SCP(Sand Compaction Pile) is one of the ground improvement techniques for loose sand or soft clay layers. The expectable ground improvement effects of SCP in soft clay layer are increase of bearing capacity, decrease of settlement and reduction of lateral ground movement. In slope stability analysis, SCP treated ground is generally considered as a composite layer. The shear strength of composite layer largely depends upon the stress distribution ratio(n), and the angle of assumed failure surface(θ). And the results of slope stability analysis are affected by methods of stability analysis. In this study, the effects of n and θ value on the slope stability analysis results are examined. And the comparisons of several stability analysis methods are carried out in order to find out the suitable method of slope stability analysis for a given area replacement ratio of SCP treated ground.

보행보조차를 사용할 때와 유모차를 보행보조도구로 사용할 때의 보행 안정성 비교

박민수(Min Su Park),조승현(Seung Hyun Cho),신선희(Seon Hee Shin),김유신(Yu Sin Kim),이승진(Seung Jin Lee),손승희(Seung Hee Son),박수희(Soo Hee Park),양영애(Young Ae Yang) 대한인간공학회 2009 대한인간공학회 학술대회논문집 Vol.2009 No.11

The purpose of this study is to find the problems of stability when people use the bassinet as an ambulatory aid for old people. Structural analysis of an outdoor rollator and a bassinet is used to check the stability of both tools. And we analyze and discover the differences of the body segment's angle and the distance from pressure cone apex to greater trochanter. This study was investigated from may 16th, 2008 to november 5th, 2008. The 13 adults who are the members of I university in Gyeongsangnam-do, Korea and don't have disorders of musculoskeletal system volunteered to participate in this study. According to structural analysis of the both tool, we compared the structural stability of the outdoor rollator with the structural stability of the bassinet. And when the participants walked using both tool, the motions are captured and analysed. The participants walked each 1 time using the outdoor rollator and the bassinet as ambulatory aid. We measured the angle of shoulder joint, trunk's angle from the ground when the participants were walking. And we found the distance from participants' pressure cone apex and greater trochanter. We analyzed the data which is collected in SPSS 15.0 use. We use a technical statistics to analyze the general quality and the result were analyzed with use of a paired sample T-test. The significance level was controlled with 0.05. Following the structural analysis, the bassinet has the lower structural stability than the outdoor rollator. And according to the gait analysis, result of shoulder angle when people use the both tools, had significant difference (p=0.002). However, the angles between ground and trunk when people use both tools, didn't have significance (p>0.05). nd the result to compare the distances from the pressure cone apex to the greater trochanter when people use the rollator with when people use the bassinet, had significant difference (p=0.000). When the people used the bassinet as ambulatory aid, the angle of the shoulder joint was bigger than to use the outdoor rollator. The angle of trunk was not a difference between to use the outdoor rollator and the bassinet. And distance from pressure cone apex to greater trochanter was far to use the bassinet than to use the outdoor rollator. Therefore, through the structure analysis and gait analysis of the bassinet and the outdoor rollator, we can be aware of that the bassinet has problem of stability and when a person uses the bassinet as an ambulatory aid, especially supporting body weight, can be occurred the problems of stability.

공기흐름을 고려한 수리-역학적 연동모델에 의한 불포화 토사사면의 안정해석

조성은 한국지반공학회 2016 한국지반공학회논문집 Vol.32 No.1

Stability analysis based on the limit equilibrium method combined with the result of infiltration analysis is commonlyused to evaluate the effect of rainfall infiltration on the slope stability. Soil is a three-phase mixture composed of solidparticle, water and air. Therefore, a fully coupled mixture theories of stress-deformation behavior and the flow of waterand air should be used to accurately analyze the process of rainfall infiltration through soil slope. The purpose of thisstudy is to study the effect of interaction of air and water flow on the mechanical stability of slope. In this study,stability analyses based on the coupled hydro-mechanical model of three-phases were conducted for slope of weatheredgranite soil widespread in Korea. During the process of hydro-mechanical analysis strength reduction technique wasapplied to evaluate the effect of rainfall infiltration on the slope stability. The results showed an increase of air pressureduring infiltration because rain water continuously displaced the air in the unsaturated zone. Such water-air interactionin the pore space of soil affects the stress-deformation behavior of slope. Therefore, the results from the three-phasemodel showed different behavior from the solid-water model that ignores the transport effect of air in the pores.

강우시 보강토 옹벽의 안정성에 관한 연구

유충식(Chungsik Yoo),김선빈(Sunbin Kim),한준연(Joonyeon Han) 한국토목섬유학회 2008 한국토목섬유학회 학술발표회 Vol.2008 No.4

Slope stability analysis is a geotechnical engineering problem characterized by many sources of uncertainty. Some of them are connected to the variability of rainfall involved in the analysis. In this paper, the limit-equilibrium slope stability analysis is presented based on pore-pressure consideration to investigate the variation of global stability factor of safety with rainfall infiltration into the reinforced wall. The results were thoroughly analyzed to get insight into the mechanism of pore water pressure reduction effect of the precipitation and soil .and into its effect on overall slope stability. Slope stability analysis was performed to obtain the practical approach with the variation of rainfall parameters and soil properties. Practical implications of the findings were discussed.