Reconnection control apparatus and power system

A reconnection control apparatus that controls a switch disposed between at least one DER system and a power grid comprising:

• the DER system having a droop characteristics that can control a phase and a frequency of an output voltage of the DER system based on a power reference signal received from the reconnection control apparatus,
• a first detector to detect a first phase and a first frequency of a voltage on a side of the DER system of the switch;
• a second detector to detect a second phase and a second frequency of a voltage on a side of the power grid of the switch;
• and
• a reconnection controller to control the DER system by outputting the power reference signal to the DER system and reconnect the DER system to the power grid by outputting a switch signal to the switch, the reconnection controller controlling the DER system so that the first phase matches the second phase and the first frequency matches the second frequency, the reconnection controller outputting the switch signal when an absolute difference between the first phase detected by the first detector and the second phase detected by the second detector is less than a specific threshold.