Unidirectional Fault Current Limiter: An Efficient Interface Between the Microgrid and Main Network

Increased fault current level may exceed the rating of the existing network´s equipment and disrupt coordination of overcurrent relays (OCRs). Introduction of new dispersed generation (DG) units in a grid connected microgrid is the main reason for increasing the fault current level. To overcome the above-mentioned problems, fault current limiters (FCLs) can be utilized between the microgrid (downstream) and main grid (upstream). Most FCLs have a bidirectional current limiting function. Whereas in the case of a fault in downstream, it is advised to disable the FCL in order to prevent some problems occurring in the microgrid. Power quality (PQ) and reliability of the microgrid as well as coordination between the upstream and downstream OCRs are affected by the bidirectional FCL in case of fault in downstream. In this paper a unidirectional fault current limiter (UFCL) is proposed to achieve a proper interaction between the upstream and downstream. During the fault condition in the main network, the UFCL acts normally; however, in case of fault occurrence or heavy load startup in downstream, the UFCL is disabled to avoid the aforementioned problems in the microgrid. Several simulations and experiments are carried out to demonstrate the effectiveness of the UFCL.