The Research On Improved AC Micro-grid Protection Algorithm Considering The Influence Of Transition Resistance

Micro-grid contains a large number of inverter-based distributed generations,which make its fault characteristics differ from traditional distribution network.It causes that the traditional relay protection algorithms in distribution network are difficult to be applied to the micro-grid directly.In addition,the actual faults often exist the transition resistance,which makes fault characteristics more complicated and fault zones more difficult to be identified.Therefore,it is a prerequisite to ensure the safe and stable operation of AC micro-grid that developing a new protection algorithm which can be applied to the new fault characteristics of micro-grid and has the ability to resist the transition resistance.Firstly,common inverter-based distributed generations in micro-grid and theirs network technologies were summarized by this paper.The fault output characteristics were analyzed and the equivalent models were established of that use constant power or constant voltage/frequency control strategy.Aiming at the fast dynamic process of Short circuit and protection,the electromagnetic transient models of conventional components in micro-grid were established.According to the different operation modes and control strategies of micro-grid,based on the equivalence principle of the same control strategy,an equivalent model of AC micro-grid was establishedSecondly,taking advantage of the relationships between voltage and current measured at both ends of the line before and after fault,an AC micro-grid protection algorithm based on the impedance measurement at both ends of the line was introduced by this paper.A problem of the above protection algorithm was proposed about insufficient resistance to transition resistance.Aiming at this problem,the influence of transition resistance on the measured impedance was analyzed,the adaptive measurement of impedance correction factor was constructed,and an improved protection algorithm was proposed.Lastly,an example of AC micro-grid simulation was given to verify that the improved protection algorithm has a certain resistance to transition resistance.