| Increasingly complication of distribution network makes fault inevitable and unpredictable in power system. It would have serious economic losses and social impacts if promptly restoration is not taken after a power fault. In recent years, as the technology matures distributed generation (DG), the penetration rate of DG is rising. DG has a negative impact on operation and protection in distribution network; however, Power Island incorporating DG is important to ensure continuity of power supply to load and improves the stability of the distribution network. Many experts and scholars have conducted a lot of research concerning island partition. This paper studied further on the basis of reviewing and summarizing the results of previous studies. The main work includes the following aspects:(1)The advantages and disadvantages of DG were reviewed and summarized, particularly the great importance of DG's islanding mode in power restoration. This paper have reviewed current means and algorithms for power restoration and island partition strategy, and pointed out potential drawbacks, which highlighted the need for this study.(2)The feasibility of isolated islanding operation model incorporating DG has been analyzed and island partition is under the circumstance that isolated island could be formed and operated stably. In this paper, some common distributed generators were listed and their characteristics and node model in the power flow calculation, which ensure the accuracy of power flow calculation model. In addition, the impact of distributed generator on losses of transmission lines, system voltage level, relay protection, development planning has been simply summarized and analyzed. "Negative impacts could be removed or eliminated by technical means as far as possible.(3)The basic requirements of island partition were proposed in distributed network and model of treelike topology of distributed network was established. Mathematic model of island partition was built based on constraints of island electrical operation, distributed generators'power capacity as well as treelike topology. Two optimization objectives to restore loads and high-priority load as much as possible were selected. Island partition problem can be regarded knapsack problem with treelike topology considered. A depth-first dynamic programming algorithm (DDPA) was adopted to form a Primary Island amended further to Secondary Island according to some amending laws considering controllability and priority of the load. Ways of amending island were to "fill" remaining active power and to "replace" lower-priority load in island by the higher-priority outside the island. Example and comparison with others showed that the objectives can be optimized by means of DDPA when the constraints were met. Amendment rules can compensate for disadvantages that the DDPA cannot handle non-integer load and optimized Primary Island further, which is the major innovation in this paper.(4) Multi-objective optimization model outside the island was established when selecting objectives of "minimum network loss", "optimal voltage quality" and "optimal load balancing". Analytic hierarchy process (AHP) was used to analyze the impact of individual loop-break solution on the target function and optimal scheme was picked according to the value of the overall objective. The example shows that the optimal loop-break solution scheme does not make all targets, even the best single target, but making the global optimum. However, AHP has a shortcoming that it cannot work when optional scheme uncountable. |
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