Study On Reliability Of Microgrid And Distribution System With Microgrids

Microgrids provide important means to improve distribution system reliabilityand promote the utilization of renewable energy. While they are increasingly used indistribution system, the corresponding reliability evaluation methods have not beenwell developed. The work of this dissertation focuses on reliability evaluation metricsand methods of microgrid, the reliability analysis of distribution system with highdensity distributed generations (DGs), and planning method for distribution systemwith microgrids. The major achievements are as follows:A series of reliability indices and related economic indices are presented basedon the structure and operation features of microgrid. These new metrics describe thereliability of microgrid from the aspects of island adequacy, DG characteristics,relationship between microgrid and distribution system. The microgrid economicmetrics include indices reflecting microgrid generation cost, energy exchangebetween microgrid and distribution system, and microgrid overall benefits status. Theproposed metrics help to provide a scientific basis for performance evaluation andplanning decisions making for microgrid.An equivalent generator model for point of common coupling (PCC) ofmicrogrid together with a two-stage sequential Monte Carlo simulation method ispresented for microgrid reliability analysis. The reliability evaluation process ofdistribution system and microgrid is decoupled at the PCC with the proposed method.Thus the impact of random distribution system failures and island switching processon the reliability of microgrid can be analyzed. Moreover, more detailed microgridoperation information can be obtained through specific simulation with a shorter stepsize.With the integration of high density distributed photovoltaic (PV), distributionsystem is supposed to have the ability of providing reliable access for PV andguaranteeing a fully consumption for the energy produced by them. The concept ofPV access reliability is proposed together with corresponding evaluation metrics toquantitatively describe this ability of distribution system. An analytical probabilitymodel is established based on history data, which can fully reflect the time correlationbetween PV output and load level. The effects of node voltage constraints and systemfaults on the reliability of load and PV access are studied separately using analytical method. A PV shedding optimization model is established to guarantee a minimumPV shedding amount and a maximum PV energy self-utilization rate with nodevoltage constraints.A reliability analysis method for distribution system with multi microgrids isproposed. Based on block minimal cut set algorithm, this method can effectivelyhandle the impact of multilayer sectionalizing characteristic of microgrid on thereliability evaluation process. The system reliability offset index is presented to reflectthe fitness between distribution system power supply capacity and diversified loadreliability requirements. An optimization model for static switches and microturbinesis established based on this index to satisfy customized reliability requirement byforming appropriate microgrids. The optimization problem is solved by an improvedimmune genetic algorithm, which uses double evolutionary mechanism of populationand vaccines library to ensure effective global search ability and local developmentcapacity.