Studies On Assistant Decision-Making Method For Power System Restoration And The System Development

With the development of power grid interconnection and long-distance AC and DC transmission technology, high-capacity units, super (ultra) high voltage equipments, power electronic devices and distributed generation technology are largely introduced into power system. Power system becomes larger and its dynamic behavior becomes more complex than before. The risk of blackout caused by partial failure has increased significantly. Since 2003, several large blackouts have occurred in North America and Canada, England, Sweden and Denmark, Italy, Greece, Kuwait, Moscow, Western Europe, Brazil and other countries. In recent 20 years, there were also more than 100 blackouts occurred in China. The actual operation of power system at home and abroad shows that new equipments and technologies can make power system operate more safely and stably, but the occurance of blackout is unavoidable. As modern society becomes increasingly dependent on electricity supply, consequences caused by blackouts become more and more serious. Once blackout occurred, measures must be taken to restore the power supply as soon as possible.As the probability of blackout is extremely small, dispatchers are commonly lack of restoration experience. After blackout, in order to make right decisions and guarantee power system restored safely and quickly, utilities urgently needs a feasible power system restoration decision-making method and the software which can provide power system restoration decision support and training simulation for dispatchers. Therefore, it is necessary to analyze the characteristics of power system restoration problem and improve restoration strategy. The decision-making method which can comprehensively coordinate system security and restoration speed should be studied to improve the existing methods on flexibility and coordination ability in dealing with large scale power system restoration. The power system restoration decision support and training simulation system, which has unified data platform and can integrate with EMS/DTS, should be designed and developed to improve the existing system in data consistency, simulation tools completeness and graphic and data maintenance. These studies have important theoretical significance and application value in expanding the theory and function of DTS system on power system restoration. They can enrich power system restoration control theory, enhance power system emergency command system and reduce blackout losses. Based on literature review of researches on power system restoration and its decision support, thorough studies on skeleton restoration decision-making method, power system restoration decision support and training simulation system and the optimal reserved water of pumped storage power station have been made in this dissertation. The main research work and innovative fruits are as follows.1) According to the actual needs of utilities on power system restoration decision support system, a group intelligent decision support system framework for power system skeleton restoration based on data warehouse is proposed. This system is composed of three parts:they are comprehensive data platform, intelligent control subsystem and group decision support subsystem. A three-stage skeleton restoration strategy is proposed to control restoration process. According to evaluation values of every benefit-oriented attribute, the multi-attribute utility theory is employed to dynamically determine the target and plan of next restoration step. The system can comprehensively consider the constrains such as transient overvoltage, sustained power frequency overvoltage, self-excitation, frequency fluctuation, units and loads characteristics, restoration duration, available transfer capability of transmission line and equipment failure probability. The comprehensive data platform can guarantee the data needed by every security verification and assessment algorithm are consistent. By using distributed computing technology assign computing tasks to different computers, restoration plan generation rate is accelerated. Intelligent control and decision support subsystem can ensure the safety and rapidness of the restoration process. Simulation results of a practical power system demonstrate that the system not only can generate feasible cases for case-based reasoning, but also can provide online supports in actual restoration process.2) Combining the subsystem paralleling restoration strategy with the restoration plan development processes, a novel group multi-attribute decision-making method for power system skeleton restoration is presented. The proposed method improves the technique for order preference by similarity to an ideal solution (TOPSIS) in supporting group decision-making. Subsequently, the combined weights can comprehensively take into account the subjective preference of decesion maker and the objective information of attribute values by combining the weighted least-square method with Shannon entropy theory. Furthermore, the ranking results sensitivity of the improved TOPSIS is analyzed and the absolute sensitive index of the optimal plan was presented by using Euclidean distance and non-linear programming method. This method can comprehensively consider the safety margin and restoration rate of power system, and can be used to support the restoration decision-making of a subsystem. Simulation results of Shandong Power Grid in China show the proposed method is feasible.3) A black start plan generation and training simulation subsystem is designed on the data and graph platform of DTS, to which the tables, fields and metafiles are added, according to the actual requirements of utilities on black start plan generation, checking, evaluation and dispatcher training. A new black start operation plan generation algorithm is proposed. This subsystem has been developed and integrated with the cross-platform DTS system. It can share database, graphics library, human-machine interface, communications platform and other modules with DTS system. In this way, the large maintenance workload of data and graphics in independent black start decision support system is saved. The extended DTS generates black start plans according to the power system conditions after blackout. Then, these plans are checked, adjusted and evaluated. The settings of protections and automatic devices are automatically verified. The system has the training simulation functions of power frequency overvoltage, transient overvoltage, self-excitation, the voltage and frequency fluctuation caused by load or large motor restoration. Simulation results of Shandong power grid show its good application prospect.4) In the power grid with a larger proportion of thermal generator set, the pumped storage power station needs not only to provide black-start ancillary service but also to meet the demands of peak load shifting, frequency regulating and so on. However, the reserve water which is used to meet the needs of black start has a direct impact on the benefits of peak load shifting. In order to obtain the largest benefits of pumped storage power station, the calculation methods for black-start benefits, static benefits, marginal running position and black-start consumed water are proposed. Considering the black-start benefits of pumped storage power station, static benefits and the constraint of marginal running position, the mathematical model of optimal reserve water is constructed. Using the data acquired from the black start field test in Shandong power grid, the generating efficiency of Taian pumped storage unit #1 in ultra low load condition is calculated, and the black-start benefits, static benefits and black-start consumed water of it is computed. Then, the main influence factors on black-start benefits, static benefits and black-start consumed water are analyzed. These results can provide reference to the operation of Taian pumped storage power station. It is the first time to introduce black start service into the operation scheduling of pumped storage power station, which improves the operation scheduling model of pumped storage power station. This method can be used in other power grids which use pumped storage power station as black start power.