A Fast Voltage Sag Evaluation Method of Distribution Systems with Inverter Interfaced Distributed Generators

The voltage sag caused by the fault may make the sensitive equipment trip and cause huge economic loss, so it is very valuable to study the voltage sag evaluation to prevent voltage sag. This paper presents a fast voltage sag evaluation method for an unbalanced distribution network with an inverter interface for distributed generators (IIDG). Rapid assessment of voltage sag needs to be based on accurate short-circuit current calculation. IIDG should operate following the low voltage ride-through (LVRT) requirement during the fault, which makes the fault current characteristics more complicated. In addition, the three-phase coupling components are difficult to decouple in unbalanced distribution systems. Therefore, the traditional symmetric component method cannot be applied in voltage sag evaluation in unbalanced systems with IIDG. In this paper, the short circuit calculation equivalent model of IIDG is analyzed. A rapid evaluation method of voltage sag based on block bordered diagonal form (BBDF) is proposed. The validity of the proposed method is demonstrated by IEEE 13-node, 123-node, 478-node, and 954-node test systems. The results show that the proposed method has obvious advantages in computational efficiency