Abstract:Vigorously developing renewable energy generation is an effective way to tackle the challenges of energy crisis and air pollution. High proportion of renewable energy integration will be one of the basic characteristics of future power systems. This paper summarizes a number of key issues for power systems with a high proportion of renewable energy generation from two aspects: the power system planning and operation under high level uncertainty and the stability mechanism of power system with massive integration of power electronic devices. On this basis, a theoretical research framework is proposed by dividing the above two scientific issues into five sub-problems: the evolution of power system structure and its forecasting model; a multi-objective planning method for AC/DC transmission network with a high proportion of renewable energy generation; the distribution system planning with a high proportion of renewable energy generation; the stability analysis of power electronics dominated power systems; the cooperative optimal operation theory of AC-DC hybrid power system with a high proportion of renewable energy generation. The relationship among the five sub-problems is described. Finally, key technologies for future power systems with a high proportion of renewable energy generation are provided and prospected.

Abstract:In the midst of clean, low-carbon and smart energy revolution, a high proportion of renewable energy integration will be one of the basic characteristics of future electric power system that leads to tremendous changes in the morphological changes. And it also introduces the morphological evolution of generation, transmission, distribution and load of the system as a whole. The topology evolution model and power forecasting method of the future electric power systems are reviewed. The elements of the electric power system morphology and driving model are described first. Then based on analyzing the development trend of high proportion renewable energy generations, a future power system morphological evolution model is proposed. Key scientific issues are concluded as: 1)morphological evolution mechanism of power system with a high proportion of renewable energy; 2)power forecasting of complex multiple uncertainty operation scenarios. Suitable research framework is divided into four aspects and analyzed in detail.

Abstract:The spatial and temporal distribution characteristics of the future high proportion of renewable energy will present unprecedented challenges to the operation and planning of power systems. Owing to the radical change in the power system basic forms and operational characteristics, it is of great significance to study the transmission expansion planning considering high proportion of renewable energy planning. Based on former researches, four aspects of transmission expansion planning are introduced including the theory and method of coordinated grid-source planning, the transmission flexible planning method, the transmission planning coordinated with distribution network and the comprehensive evaluation and decision-making method of the transmission planning scheme. Finally, the key issues and prospects for future power systems with a high proportion of renewable energy are provided.

Abstract:The security boundary based planning idea and research scheme for the distribution system with high penetration of renewable energy generation are proposed. Firstly, the problems of the distribution network in China caused by integration of renewable energy generation are discussed. It is pointed out that the system security is the bottleneck limiting the high proportion of renewable energy generation while the security boundary, which is an effective way to break through the limitation, can describe the maximum operation range of a system when N-1 guideline is considered. Then, it has been found that the model, characteristics and mechanism of security boundary will significantly change in the scenario of high proportion of renewable energy generation: the range of security boundary will transform to a total-quadrant region from a single-quadrant region; the function and security characteristics will differ a great deal with an increase in penetration. Thus, it is necessary to determine the critical penetration rates which will cause essential changes of security. Finally, a security boundary based planning idea is proposed: 1)The network configuration will be selected based on the index of security boundary, such as shapes, and the controllable components, such as energy storage and active load, should be optimized. 2)The two planning methods for the scenarios of high-load density in urban area and rich renewable energy in rural area. 3)The generalized source-load index is developed by referring to the load ratio, to guide the practical planning. 4)New test system and simulation platform for distribution network planning is developed.

Abstract:With the rapid development of wind power and solar power generation as well as steady development of AC and DC transmission lines, China's power system exhibits two important characteristics and trends: high proportion of renewable energy and AC/DC hybrid power grid in recent years. Based on an analysis of the present development and existing problems concerning collaborative optimization operation of AC/DC hybrid system with a high proportion of renewable energy, the key technologies demanding prompt research in four aspects are proposed, respectively. That is, situation awareness of AC/DC hybrid system under dual uncertainties of source and load, coordinated control of large renewable energy clusters considering the broadband stability constraints, flexible reconfiguration and cooperative operation with the interaction of source-grid-load in distribution systems with a high proportion of renewable energy, and multi-scale operation optimization and decision making in AC/DC hybrid system with a high proportion of renewable energy integrated. Difficulties and challenges are previewed.

Abstract:Power systems are now facing challenges in terms of safety, stability and economic efficiency with penetration of a great number of distributed resources(DRs). Transactive energy(TE)has become a hot research area for its promises on supply-demand balance. Considering the current development of DR, the TE is limited to distributed systems when facing the distributed agents such as end-users, DR, and distributed storage. In our mechanism, the distributed agents can communicate and trade directly with each other which form a decentralized and flat trading system. Such transactions feature spot electricity prices so that the interests of members and the system are incentive compatible. Firstly the TE's concept is elaborated and its characters and significance are listed. Secondly TE's architecture and trading mechanism are designed comprehensively. Then, TE's operational process is presented and the benefits of all related members are discussed. Finally the key technologies for TE, such as the intelligent decision system and block chain, are briefly described from the perspective of system operation requirement.

Abstract:The state-of-the-art development of spatial correlation based wind speed prediction is reviewed. And the concepts of conditional correlation and its corresponding confidence correlation are introduced to improve traditional spatial correlation. Based on big-data thinking, a framework of integrating data-driven with causality-driven wind speed prediction is proposed. In the framework, correlation is mined from historical data for wind speed prediction. Spatial correlation is employed to import data sources for wind speed prediction to overcome the shortage of historical data in part. Furthermore, spatial correlation with long time lag can be used to predict drastic and sudden change in downstream wind speed. Finally, suggestions for future research under the proposed framework can be made with confidence. This work is supported by the State Key Program of National Natural Science Foundation of China(No. 61533010), NSFC-NRCT(Sino Thai)Cooperation Research Project(No. 51561145011)and State Grid Corporation of China.

Abstract:Highly volatile distributed generators(DGs), large scale electric vehicles and various controllable demand-side resources have increasingly been integrated into smart distribution networks. It puts forward a higher requirement for the flexibility of distribution networks to cope with the various uncertainties. Characteristics of the flexibility are analyzed from the point of view of the evolution of future distribution networks. The demand and multi-dimensional characteristics of distribution network flexibility are elaborated. The key technologies, including the observability, controllability and quantitative analysis of the flexibility, are discussed. Finally, a preview is performed from the perspective of flexibility for the future development of distribution network planning, operating and control technologies.

Abstract:The future distribution system will have the significant characteristics such as high density integration of distributed generations, interconnection of AC/DC hybrid system. Therefore, the fault analysis for distribution system will face new challenges. As the integration of high density distributed generation and power electronic equipments, the fault response presents the property of nonlinear temporal-spatial correlation, and the fault response interaction influences between AC/DC system further increase the difficulty of fault analysis. In this paper, the current research status of the distribution system fault analysis is summarized, and the key issues to be studied in the future are proposed including the analysis and decoupling modeling of distributed generations for the temporal-spatial correlation characteristics, the equivalent modeling of AC/DC hybrid distribution system, and the effective convergence algorithm.