| During the 12 th five-year plan period, in order to satisfy the rapid development of power load, installed capacity and the scale of power grids of China Southern Grid Corporation have increased rapidly. The eight AC transmission lines and eight DC transmission lines have been forming from west to east in southern China, which supply 34 million k W power in the whole area. Meanwhile, electrical connection in power grid becomes more and more closed, short-circuit current of several 500 k V substations approach or exceed the breaking capacity of circuit breakers, which threats the safe operation of the power grid seriously. Therefore, short-circuit current have become the threats of power grid operation and development. Taking measures to limit short-circuit current are around the corner. In this paper, the main creative results are as follows.1) Based on the research of optimal power flow optimization model including voltage source converter-based high voltage direct current(VSC-HVDC), this paper presents a multi-objective optimization model of short-circuit current limiting measures. The model includes these measures as follow: to adjust the network structure of power system, to allocate current limiting reactor and to allocate back-to-back VSC-HVDC system. The objective function involves optimal economy of investment, short-circuit current minimum and reliability index EENS(Expected Energy Not Supplied) minimum. The constraint in this model includes AC system safe operation, VSC-HVDC system safe operation and short-circuit current limiting, etc. The proposed model is a mixed integer nonlinear programming(MINLP) problem which is solved by the non-dominant sorting genetic algorithm-II(NSGA-II) in the upper model and the original dual interior point algorithm used to calculate EENS index in the lower model. Finally, Pareto optimal set of short-circuit current limiting measures is found to satisfy the above objective functions.2) Based on analyzing the principle of using VSC-HVDC to reduce short-circuit current, multi-objective optimal allocation model of VSC-HVDC is established, which involves the following objectives: to optimize comprehensive effects of reducing short-circuit current and to optimize economy of investment. The non-dominated sorting genetic algorithm-II is employed to solve the proposed model. In order to improve the speed of individual fitness evaluation, the multi-port network equivalent model reduces the feasible solution space. The fuzzy selection strategy is used to obtain optimal compromised phased construction scheme. Taking Guangdong power grid’s operational plan in 2015 summer as a case, it is demonstrated that the proposed model and method can provide references for power grid enterprises to plan power grid.3) Considering actual situation of multiple infeed DC of Guangdong power grid, this paper introduces the multiple infeed DC short-circuit ratio index, which is used to evaluate the system security and stability. The multi-objective optimization model of multiple infeed DC grid contain the short-circuit ratio of multiple infeed DC system, limit of short-circuit current and economic. Considering the great and complex power grid, sensitivity analysis is adopted to satisfy the accuracy and calculation speed based on multi-port equivalent models. The 2015 summer mode of Guangdong power grid is used to testify the effectiveness of model and method, to looking for sequential measures of short-circuit current limiting which satisfies the engineering practice. In this paper, the advantages and disadvantages of the two schemes of VSC-HVDC applied to power substation or transmission line are analyzed and compared. |
PDF Full Text Request