*4.3. TFRT Algorithm*

The FRT in the conventional grid code allows DG to continue operation without disconnection in the event of a fault in transmission systems, but under this condition, it cannot be applied in the event of a temporary fault in distribution systems. This is because the fault conditions of transmission systems and distribution systems are different, as described in the introduction. Therefore, this paper proposes a Temporary Fault Ride-Through (TFRT) algorithm so that DG can continue to operate in the temporary fault condition. The TFRT algorithm using the controller described in Sections 4.1 and 4.2 is shown in Figure 7. If a fault is detected on a feeder, the CB or recloser opens with their first fast operation, and then DG will run in islanding operation. If the unbalanced voltage continues until the reclosing operation of the CB or recloser, DG perceives the fault as permanent fault and is disconnected from the PCC. If the voltage is balanced, DG perceives the fault as a temporary fault and conducts control to maintain the voltage within a permissible operating range of the VRT. Here, the reference voltage value *VRMS* was determined as 0.5 p.u., considering the VRT operating range of IEEE 1547. When the fault is eliminated and the CB or recloser is reclosed, the proposed controller suppresses inrush current to minimize severe or critical damages to DG and distribution systems.

**Figure 7.** Proposed fault ride-through processing for a temporary fault. PCC: Point of Common Coupling.
