Research On DC Power System Of Off-grid Island

Rich in resources, island has both important economic and strategic significance. Energy supply is essential for producing and living on the island. Currently, the ways of energy supply on the island are mainly long-distance power transmission or diesel generators. Both of the ways can not meet the economic and environmental requirements.Islands is rich in renewable energy. The rapid development of distributed generation technologies, power electronics technology and storage technologies, can make island complementary power generation system design possible. Currently many countries began to try more renewable energy combination of energy supply system, but most of the researches are still at an exploratory stage, which are designed and constructed for a specific island.Based on the characteristics of island power supply, load and power system topology, the criteria of distributed micro-grid island power supply system is proposed. Under the guidance of the above criteria, two structure designs of island DC microgrid suiting different island geographical environment, load types and power distribution are proposed. Finally, the economy and reliability of the islands’ microgrid are calculated and analyzed.Firstly, the main characteristics of island renewable resources and output are analysised. Then, a reasonable classification of various types of load on the island is proposed based on the demand for electricity. These works provide the basis for the following criteria of distributed micro-grid island power supply system.Secondly, considering the geography factor, load type and the resource distribution of the island, several criteria of island microgrid design are given, including the power reliability of island grid, the economy of island grid construction and operation, the full utilization of resources, and the system flexibility. Under the guidance of the above criteria, two structure designs of island DC microgrid suiting different island geographical environment, load types and power distribution are proposed, including the star topology with main power supply and auxiliary power supply and the annular topology with multiple distributed generators.Finally, the micro-grid topologies are compared from the economy and reliability angles. Combining the existing island AC microgird topology, the capital cost and operating cost of the three micro-grid topogolies are calculated and the economic index are compared, which provides a new way to establish evaluation of micro-grid on the island. Basing on the minimum-cut set method, the reliability index of these three topologies are calculated, which gives the advantages and disadvantages of these topologies and the range of their application.The paper not only provides a good reference to the island micro-grid power system planning, design and actual project construction, but also gives a new way to establish an economy and reliability assessment for micro-grid on the island.