Study On Stochastic Modelling And Assessment Of Microgrid And Multi-microgrids System

Distributed renewable energy,energy storage system and load can constitute a microgrid to be integrated into distribution system,which weakens the impact of intermittent distributed renewable energy to distributon system and improves the distributed renewable energy hosting capacity of distribution system.Connecting nearby microgrids into a multi-microgrids system can deal with the problem that the output of distributed renewable energy is uncertainty and improve reliability and economic behavior of microgrids.This thesis focuses on stochastic modelling and assessment of microgrid and multi-microgrids system.The major achievments are as follows:Wind speed variability is an important characteristic of wind energy.In addition,wind energy also has an important gusty characteristic,which means that the wind will last for a certain period under a certain level of wind speed.Considering the probabilistic characteristic of wind speed and the gusty characteristic of wind energy,a two-dimensional wind speed statistical model is proposed in this thesis.The first dimension of the proposed wind model focuses on the probability distribution on the time duration of different wind speed scales,while the second dimension focuses on the probability distribution of wind speed in each wind speed scale.This thesis also presents a two-dimensional wind statistical model based data sampling method,and incorporates it into the microgrid reliability assessment algorithm.Considering the fact that the distributed generators are installed dispersedly in multi-microgrids system,a stochastic correlation modeling method using the pair-copula method is presented in this thesis to capture the multiple stochastic correlations for wind speed data,solar insolation data separately.Affected by the constitution of different type's loads,the load in different microgrids may have different variation characteristics.A stochastic correlation modeling method based on the pair-copula method is proposed in this thesis to capture the multiple stochastic correlations among different load measurement data.The procedure for generating a synthetic set of stochastic correlated data based on pair-copula method is also presented in this thesis.The proposed modeling method and data generating procedure are incorporated into multi-microgrids system reliability evaluation algorithm.Considering the structure characteristics of multi-microgrids system,four kinds of multi-microgrids system topologies are proposed in this thesis,which includes: parallel connection multi-microgrids system,series connection multi-microgrids system,nested multi-microgrids system and multi-points distributed access multi-microgrids system.Considering operation characteristics of multi-microgrids system,a series of new metrics for assessing the performance of multi-microgrids system is proposed in this thesis.These metrics can be divided into four categories: 1)power and load related metrics;2)power exchange related metrics;3)reliability related metrics;4)economic related metrics.Considering operation characteristics of multi-microgrids system,this thesis proposes a multi-microgrids system operation assessment algorithm under two modes: grid-connected mode and islanded mode.A multi-microgrids system performance assessment algorithm is proposed to assess the interactivity and economics of a multi-microgrids system which is operated in grid-connected mode.A multi-microgrids system performance assessment method is proposed to assess the reliability,interactivity and economics of a multi-microgrids system which is operated in islanded mode.The proposed method is able to consider the energy exchange in multi-microgrids system and the different characteristics of critical load and non-critical load in multi-microgrids system.Also,the total energy capacity constrains of energy storage system is proposed in this thesis.Finally,an annual performance assessment algorithm for multi-microgrids system is proposed in this thesis.