Implementation of sliding mode control with variable structure of a series active power filter main circuit is studied in this paper. The model of a series active power filter main circuit is built first. The design of control rule function is the emphasis of variable structure control mechanism. However, the value of control law is limited between two state, which makes the design of sliding surface function become more important in APF. The paper deduced each variable of sliding mode control for design schemes and presents the selection of control rules. Computer simulation demonstrates that compared with triangle carrier wave mode control mechanism, sliding mode control has superior characteristics.Index Terms-series active power filter， sliding mode control ， variable structure

Microgrid is profitable to mitigate the expansion pressure of transmission grid and achieve higher reliability at the same time. It also provides an ideal platform for the application of renewable energy. Network characteristics analysis is the basic element in reliability assessment of microgrid. This paper discusses two methods of microgrid construction according to China's distribution system, and constructs a microgrid based on typical 10kV distribution network. In order to analyze the topology characteristics of a microgrid, two typical kinds of matrices are used to describe the topology of microgrid, and a more common microgrid based on RBTS Bus4 System is established to illustrate four kinds of sub-network type under different conditions. Issues analyzed in this paper clear the structure difference between the microgrid and distribution network. Accordingly, the algorithms suitable to identify the characteristics of network structure in reliability analysis of microgrid are offered. The work in this paper lays a foundation for further reliability assessment of microgrid.

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