| With the rapid development of distributed generation,microgrid technology has become an effective measure to integrate distributed generations to improve the efficiency of distributed generation and effectively alleviate energy pressure.However,a large number of distributed generations access to the microgrid system which changes the power flow structure and operation mode of the passive distribution network,making the fault location process more complicated.and resulting in the traditional electrical network protection scheme no longer applicable to the microgrid system.Therefore,the technology and principle applicable to microgrid protection should be studied for the microgrid system to promote the development of microgrid and improve the utilization rate of renewable energy.In view of this,this paper focuses on the protection of microgrid,aiming to study new technologies and principles applicable to microgrid protection and promote the development of microgrid technology.The main work of the paper is as follows:(1)This paper first analyzes the structure of the microgrid and its control types,and studies the fault characteristics of the microgrid and its impact on protection.When external faults occur in the microgrid,both the electrical network and the microgrid will provide short-circuit current to the fault point.According to the different fault location,the influence of the access of the microgrid on the original protection is analyzed.It is concluded that the shunting and augmentation effects of microgrid will lead to the expansion of traditional current protection,loss of selectivity,maloperation and rejection.(2)When the short circuit fault occurs inside the microgrid,the fault characteristics of the inverter distributed generation are analyzed,and the corresponding mathematical model is established.Then,according to the distance between the fault occurrence point and the distributed generation,the fault output characteristics of the distributed generation under different control strategies and the fault status of the feeders of in microgrid are studied.(3)The positive sequence fault component current is not affected by the power supply and load of the system,so it can adapt to the characteristics of various operation modes of the microgrid.According to the phase characteristics of the positive sequence fault component current,this paper proposes a microgrid protection scheme based on the phase comparison of the positive sequence fault component current.When the positive sequence fault component current of the bus flow to the connected feeder is in phase,it indicates that the bus fails;if not,the feeder fails.And the fault location is further determined according to the criterion.Themethod is completely independent of the operation mode of the microgrid,and can minimize the effect of the distributed generation access on the relay protection.(4)In order to shorten the fault location time of microgrid system with a large number of complex branch lines,this paper further proposes a microgrid protection strategy based on hierarchical thinking,which divides the faults into three types: external faults of microgrid,bus faults of microgrid and feeder faults.Firstly,a new type of directional element is proposed.Then,according to the characteristics of positive sequence fault shunt current,the fault location of external microgrid,internal busbar of microgrid and the main line where the fault is located is carried out.If the main feeder connected by the fault line is determined,then the fast fault location of feeder branch is realized by using the matrix protection algorithm constructed.This method can not only locate a single fault of the feeder branch,but also apply to the loss of fault information.(5)Finally,the simulation experiment is carried out based on MATLAB/Simulink.The results further verify the reliability and correctness of the protection algorithm and summarize the work of this paper.At the same time,the next research direction is put forward. |
PDF Full Text Request