A Multi-state Model for the Adequacy Assessment of an Autonomous Microgrid Based on Universal Generating Function

With the increasing penetration of renewable energy, the uncertainty of the natural resources such as wind and solar power will affect the reliable operating of an autonomous microgrid. Based on the universal generating function (UGF) method, this paper introduced a multi-state probability model used for adequacy assessment of an autonomous microgrid and also proposed a calculation methodology of two prevailing reliability indices including loss of load probability and expected energy not supplied. The introduced multi-state models are used to capture the uncertainty of wind speed and ground illumination intensity, and of random failure characteristics of the mechanical hardware of a wind turbine and a photovoltaic system. In view of the combination explosion shortcoming of the UGF dealing with large-dimensional multi-state space, a collecting like-item technique combined with the apportionment method are utilised to reduce the amount of states and the computational burden. The proposed models are applied to a microgrid test system, based on which are investigated the impacts of the mechanical failure of components considering the topology of wind turbine and photovoltaic system, and also the configuration of installed capacity of renewable energy on the values of two indices. This simulation results can provide valuable reference for planning, designing or operating an autonomous microgrid system.