Research On Fault Analysis And Protection Configuration Of DC Microgird

With the increasing development and large-scale application of distributed power sources and the increasing of sensitive and important loads,the reliability and power quality of various types of microgrids are getting more and more attention.It's becoming more difficult for the traditional AC microgrid to meet the requirements of reliability,cleanliness,and economy.The development of DC microgrids has become an inevitable trend.However,the size of the DC microgrid is small and the lines are short,the existence of various types of distributed power sources makes the circuit current more complicated.When faults occur in the DC microgrid,single protections cannot adapt to the complex current and voltage changes of the microgrid.The scope of this thesis covers the grid structure,fault features and protection configuration of DC microgrid.Selecting a radiation-type DC microgrid as the research object,a brief introduction of each module of the microgrid is made,and the TN-S DC system grounding method is selected.Faults can be divided into bus faults,faults of branch circuit,and faults on the DC side of grid-connected inverters according to the location of the fault.According to the type,they can be classified into inter-pole faults and pole-ground faults.Taking the faults between the poles and poles of the branch connection line as an example,a theoretical analysis of the fault characteristics of each loop is made.The commonly used DC system protection equipment and methods are introduced.Based on the results of fault analysis,the protection scheme for pole-ground faults and inter-pole faults is configured.Based on the relationship between the fault current direction and the fault location,The definition of the positive direction of protection was introduced by the scheme.Utilizing the determination of the direction of the fault current in the protection installation,combined with over-current and low-voltage protection,current differential protection,and ground current protection,the solution completes the DC micro-grid protection configuration.It meets the requirements of relay protection for selectivity,sensitivity,quick motion,and reliability.