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Liu Y.,North China Electrical Power University | Jing P.,The Smart Grid Research Institute of SGCC | Li G.,North China Electrical Power University | Zhou F.,The Smart Grid Research Institute of SGCC | And 3 more authors.
Zhongguo Dianji Gongcheng Xuebao/Proceedings of the Chinese Society of Electrical Engineering | Year: 2015

It was described that the mesh network mode, insteading of the widespread end-to-end mode, would become the mainstream of the power transmission of the DC grid, due to being in line with the trendy of the technologies and needs development of the power grid. It was pointed out that the power transmission optimization strategy of the DC grid, aiming to meeting the requirements of security, economic, market and environment, and so on, had solid theoretical foundation together with potential of implementation in projects, due to being based on the high controllability of the operation, decoupling between active and reactive power control, decoupling between AC and DC grid simulation, improving technology economy of devices and engeering aspects. Based on the characteristics of the space-time distribution, the strong connectivity of the network structure, power transmission separation, and so on, aiming to realization of harmonization between accuracy and complexity of mathematical models and their solution algorithm, the proposed technological roadmap includes adopting the network flow analysis method, introducing the principle of user-optimized equilibrium (UE), transferring the constraint conditions into mathematical equations and inequalities, utilizing some reasonable assumptions conditions, establishing Beckmann transmission optimization distribution mathematical model, utilizing Frank-Wolfe algorithm to obtain the global unique optimal solution, verifying its correctness and advantages by an example. Moreover, the limitations were analyzed in the aspects of the line costs, the network structures, the line losses, the power and load changes, the capacity of the DC lines, and so on, and inconsistencies and its causes of operation performances were researched between the simulation model and the real system. Meanwhile, some further research aspects were proposed, including improving and standardizing simulation models, pursuing efficient algorithm, introducing security constraints, implementing dynamic optimization, and so on. © 2015 Chin. Soc. for Elec. Eng.


Liu Y.,North China Electrical Power University | Jing P.,The Smart Grid Research Institute of SGCC | Li G.,North China Electrical Power University | Zhou F.,The Smart Grid Research Institute of SGCC | Chen Y.,The Smart Grid Research Institute of SGCC
Zhongguo Dianji Gongcheng Xuebao/Proceedings of the Chinese Society of Electrical Engineering | Year: 2015

Due to various outstanding advantages, the DC power grid has a great potential to be used in the future power grid. The design of structure and strategies of the power control is a fundamental issue of the planning, construction and operation of the DC power grid. By analyzing the similarities and differences between the ac and DC power grid control system' functions in controlling executors, the control objects, the power characteristic curves, the response speeds, and so on, each single layer's structure and function of the power control system were defined. The primary control layer is responsible for the DC voltage stability, the secondary one is in charge of the power transmission according to the dispatching orders, the third one aims at the economic load dispatching, the forth one focuses on the fault insulation and resume in the enormous range of time scales. The former three control functions are applied in the normal operation conditions, and the last one works in the occasion of the grid structure changing and the operation conditions switching. The control strategies, the operation modes and the technical routes of each layer were investigated. The key parameters and coordinations skills among different layers were studied, including the transferring calculation results, the controlling of responsive speeds, the treatment of communication delays, the ordering of updating periods and so on. The key factors, such as the reserve capacity, the communication conditions, the short-crcuit capacity of the ac systems, etc. were also studied. The proposed scheme in this paper has lots of advantages, such as utilizing the existing ac technical and managerial experiences, being The National High Technology Research and Development of China 863 Program (2015AA050101); Key Technology Project of State Grid Corporation of China (5455DD150008, 5455DD150015) compatible to the present technological and managerial structure, improving the research level and speeding up construction steps of the dc power grid. Meanwhile, the author also suggested that further studies should especially focus on promoting the control structure standard, increasing the strategies design differentiation, improving the simulation efficiency, increasing the research methods etc. © 2015 Chin. Soc. for Elec. Eng.

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