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Abstract

Wind power integration through the voltage source converter-based high-voltage direct current (VSC-HVDC) system will be a potential solution for delivering large-scale wind power to the “Three-North Regions” of China. However, the interaction between the doubly-fed induction generator (DFIG) and VSC-HVDC system may cause the risk of subsynchronous oscillation (SSO). This paper establishes a small-signal model of the VSC based multi-terminal direct current (VSC-MTDC) system with new energy access for the problem, and the influencing factors causing SSO are analyzed based on the eigenvalue analysis method. The theoretical analysis results show that the SSO in the system is related to the wind farm operating conditions, the rotor-side controller (RSC) of the DFIG and the interaction of the controller in the VSC-MTDC system. Then, the phase lag characteristic is obtained based on the signal test method, and a multi-channel variable-parameter subsynchronous damping controller (SSDC) is designed via selecting reasonable parameters. Finally, the correctness of the theoretical analysis and the effectiveness of the multi-channel variable-parameter SSDC are verified based on time-domain simulation.
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Bibliography

[1] Tang G.F., HVDC based on voltage source converter, China Electric Power Press (2010).
[2] Li C.S., Li Y.K., Guo J., He P., Research on emergency DC power support coordinated control for hybrid multi-infeed HVDC system, Archives of Electrical Engineering, vol. 61, no. 1, pp. 5–21(2020).
[3] Liu T.Q., Tao Y., Li B.H., Critical problems of wind farm integration via MMC-MTDC system, Power System Technology, vol. 41, no. 10, pp. 3251–3260 (2017).
[4] Wu J.H., Ai Q., Research on multi-terminal VSC-HVDC system for wind-farms, Power System Technology, vol. 33, no. 4, pp. 22–27 (2009).
[5] Chen C., Du W.J., Wang H.F., Review on mechanism of sub-synchronous oscillations caused by gridconnected wind farms in power systems, Southern Power System Technology, vol. 12, no. 1, pp. 84–93 (2018).
[6] Amin M., Molinas M., Understanding the origin of oscillatory phenomena observed between wind farms and HVDC systems, IEEE Journal of Emerging and Selected Topics in Power Electronics, vol. 5, no. 1, pp. 378–392 (2017).
[7] Wang W.S., Zhang C., He G.Q., Li G.H., Zhang J.Y., Wang H.J., Overview of research on subsynchronous oscillations in large-scale wind farm integrated system, Power System Technology, vol. 41, no. 4, pp. 1050–1060 (2017).
[8] Jiang Q.R., Wang L., Xie X.R., Study on oscillations of power-electronized power system and their mitigation schemes, High Voltage Engineering, vol. 43, no. 4, pp. 1057–1066 (2017).
[9] Xie X.R., Liu H.K., He J.B., Liu H., Liu W., On new oscillation issues of power system, Proceedings of the CSEE, vol. 38, no. 10, pp. 2821–2828+3133 (2018).
[10] Wang L., Yang Z.H., Lu X.Y., Prokhorow A.V., Stability analysis of a hybrid multi-infeed HVDC system connected between two offshore wind farms and two power grids, IEEE Transactions on Industry Applications, vol. 53, no. 3, pp. 1824–1833 (2017).
[11] Kunjumuhammed L.P., Pal B.C., Oates C., Dyke K.J., Electrical oscillations in wind farm systems: analysis and insight based on detailed modeling, IEEE Transactions on Sustainable Energy, vol. 7, no. 1, pp. 51–61 (2016).
[12] Sun K., Yao W., Wen J.Y., Mechanism and characteristics analysis of subsynchronous oscillation caused by DFIG-based wind farm integrated into grid through VSC-HVDC system, Proceedings of the CSEE, vol. 38, no. 22, pp. 6520–6533 (2018).
[13] Song S.H., Zhao S.Q., Analysis of sub-synchronous oscillation of DFIG-based Wind Farm integrated to grid through VSC-HVDC system based on torque method, Power System Technology, vol. 44, no. 2, pp. 630–636 (2020).
[14] Bian X.Y., Ding Y., Mai K., Zhou Q., Zhao Y., Tang L., Sub-Synchronous oscillation caused by grid-connection of offshore wind farm through VSC-HVDC and its mitigation, Automation of Electric Power Systems, vol. 42, no. 17, pp. 25–39 (2018).
[15] Lyu J., Dong P., Shi G., Cai X., Li X.L., Subsynchronous oscillation and its mitigation of MMC-based HVDC with large doubly-fed induction generator-based wind farm integration, Proceedings of the CSEE, vol. 35, no. 19, pp. 4852–4860 (2015).
[16] Lyu J., Cai X., Amin M., Molinas M., Sub-synchronous oscillation mechanism and its suppression in MMC-based HVDC connected wind farms, IET Generation, Transmission and Distribution, vol. 12, no. 4, pp. 1021–1029 (2018).
[17] Shao B.B., Zhao S.Q., Pei J.K., Li R., Subsynchronous oscillation characteristics analysis of gridconnected direct-drive wind farms via VSC-HVDC system, Power System Technology, vol. 43, no. 9, pp. 3344–3355 (2019).
[18] Chen B.P., Study on characteristics and suppression of sub/super-synchronous oscillation caused by power system with D-PMSG and VSC-HVDC, Wuhan University (2018).
[19] Guo X.S., Li Y.F., Xie X.T., Hou Y.L., Zhang D., Sub-synchronous oscillation characteristics caused by PMSG-based wind plant farm integrated via flexible HVDC system, Proceedings of the CSEE, vol. 40, no. 4, pp. 1149–1160+1407 (2020).
[20] Sun K., Mechanism and characteristics analysis of subsynchronous oscillation caused by DFIG-based wind farm integrated into grid through VSC-HVDC system, Huazhong University of Science and Technology (2018).
[21] He J., Li Q., Qin S.Y., Wang R.M., DFIG wind turbine modeling and validation for LVRT behavior, IEEE PES Innovative Smart Grid Technologies, Tianjin, pp. 1–5 (2012).
[22] Lu X.J., Lin W.X., Wen J.Y., Li Y.F., Wu Y.L., An T., Modularized small signal modeling method for DC grid, Proceedings of the CSEE, vol. 36, no. 11, pp. 2880–2889 (2016).
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[24] Zhou G.L., Shi X.C., Fu Ch.,Wei X.G., Zhu X.R., VSC-HVDC discrete model and its control strategy under unbalanced input voltage, Transactions of China Electrotechnical Society, vol. 23, no. 12, pp. 137–143+159 (2008).
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[26] Jiang P., Hu T., Wu X., VSC-HVDC multi-channel additional damping control suppresses subsynchronous oscillation, Electric Power Automation Equipment, vol. 31, no. 9, pp. 27–31 (2011).
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Authors and Affiliations

Miaohong Su
1
ORCID: ORCID
Haiying Dong
1 2
Kaiqi Liu
1
Weiwei Zou
1

  1. School of Automatic and Electrical Engineering, Lanzhou Jiaotong University, China
  2. School of New Energy and Power Engineering, Lanzhou Jiaotong University, China
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Abstract

In the last period of her professional career, Antonina Kłoskowska focused on issues related to national culture and nation itself, which is evident e.g. in her publication National Cultures at the Grass-Root Level. The article presents Kłoskowska’s main agruments concerning the notion of “national culture”. The author regarded this specific type of culture as one that could be characterized as symbolic, compound and coherent in the syntagmatic sense. Kłoskowska points out that, in order to be recognized as a member of a national community, it is necessary to acquire and refer to the canonical resources of its culture.

In the second part of the article some of the findings of contemporary Polish researchers are laid out, which correspond or directly relate to some of Kłoskowska’s ideas. A comparison and analysis of their views leads to a conclusion that their diversification does not generally mean that they are completely distant in their judgments but rather that various aspects are stressed in different ways. This attests, however, to the fact that the authors belonged to diverse intellectual formations.

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Authors and Affiliations

Leszek Baran
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Abstract

Ethicists have thus far not paid much attention to uncertainty, very often concentrating on highly idealized hypothetical situations where both empirical (e.g. the state of the world, the spectrum of possible decisions and their consequences, the causal connections between events) and normative (the content of norms, value scales) matters were clearly defined and well-known to the decision-maker. In this article, which stems from a project on different types of decisions under uncertainty related to the rapid progress in biomedical research, I analyze some situations of normative uncertainty, cases when an agent must make a decision, but does not know which choice is correct, for example, because he/she has contrary intuitions about the permissibility of available decisions. The view termed comparativism claims that in such cases the appropriate decision depends not only on the credences that one assigns to different norms, but also on how much possible decisions are worth taking in the light of these norms. I analyze a few cases of normative uncertainty, and a specific counter-argument against the current versions of comparativism, showing that under normative uncertainty this view imposes risk neutrality, although it permits us to have different risk attitudes under empirical uncertainty. I also argue that a precautionary approach to situations of normative uncertainty is overly simplistic.

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Authors and Affiliations

Tomasz Żuradzki
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Abstract

A military danger zone is a specially designated part ofthe open sea, together with the air space above it, which is temporarily or permanently given over to purposes of conducting experiments with new types of weaponry and technology, and to that of training naval forces under conditions that are as close to real ones as possible. Third party states have only limited access to military danger zones, or are forbidden to use them altogether. Officially declaring part of the sea a danger area protects the safety of international maritime navigation and air transport while dangerous military activities are being conducted in that area.
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Authors and Affiliations

Marek Ilnicki
Andrzej Makowski
ORCID: ORCID
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Abstract

The effect of multiple Rushton impellers configurations on hydrodynamics and mixing performance in a stirred tank has been investigated. Three configurations defined by one, two and three Rushton impellers are compared. Results issued from our computational fluid dynamics (CFD) code are presented here concerning fields of velocity components and viscous dissipation rate. These results confirm that the multi-impellers systems are necessary to decrease the weaken zones in each stirred tanks. The experimental results developed in this work are compared with our numerical results. The good agreement validates the numerical method.

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Authors and Affiliations

Zied Driss
Sarhan Karray
Wajdi Chtourou
Hedi Kchaou
Mohamed Salah Abid
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Abstract

Light-weight Self-Compacting Concrete (LWSCC) might be the answer to the increasing construction requirements of slenderer and more heavily reinforced structural elements. However there are limited studies to prove its ability in real construction projects. In conjunction with the traditional methods, artificial intelligent based modeling methods have been applied to simulate the non-linear and complex behavior of concrete in the recent years. Twenty one laboratory experimental investigations on the mechanical properties of LWSCC; published in recent 12 years have been analyzed in this study. The collected information is used to investigate the relationship between compressive strength, elasticity modulus and splitting tensile strength in LWSCC. Analytically proposed model in ANFIS is verified by multi factor linear regression analysis. Comparing the estimated results, ANFIS analysis gives more compatible results and is preferred to estimate the properties of LWSCC.

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Authors and Affiliations

B. Vakhshouri
S. Nejadi
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Abstract

Author proves that historical myth we can perceive as some kind of structuralization of experiencing world and history, as an instrument or device which historians use for ordering the material and imaginations.
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Authors and Affiliations

Marek Woźniak

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