*4.2. Inrush Current Suppressing Controller*

When the CB or recloser recloses, inrush current occurs due to the magnitude and phase difference of voltage between both their terminals. Since the inrush current has a negative effect on the PCS equipment and feeders, a control method of suppressing the inrush current is necessary. The magnitude of the inrush current *Iinrush* is derived as Equation (3) in the equivalent circuit of Figure 5, which is fed into DG and load. At this time, at the PCC of DG, the derivative value of current *Iderivative\_max* flowing into DG is measured and multiplied to voltage reference *Vd*,*q*\_*re f erence* to be controlled as shown in Figure 6. Then the output current *IDG* from DG is shown in the blue line and offsets the inrush current *Iinrush* shown in the red line in Figure 5. This control is implemented during a few cycles just after reclosing.

$$I\_{inrush} = \frac{V\_S \angle 0^\circ - V\_R \angle \theta}{R + jX} \tag{3}$$

**Figure 5.** Equivalent circuit of current flowing in distribution systems with DG and loads.

**Figure 6.** Block diagram of inrush current suppressing controller. LPF: Low Pass Filer, S; Differentiator, DFT: Discrete Fourier Transform.

*Iinrush* Current amplitude when recloser reclosing.

