Nano grid protection device, large power grid and a method for controlling a nano grid protection device

A method for controlling a nano grid protection device for a nano grid with a distributed power supply, the nano grid being connected with a bus through the nano grid protection device, a branch circuit and the nano grid being connected in parallel to the bus through at least one branch protection device, and a main grid being connected with the bus through a main grid protection device, the method comprising:

• receiving current information and voltage information passing through the nano grid protection device, the current information including a magnitude and a direction of the current, and the voltage information at least including a magnitude of a voltage;
• and
• determining, based upon the current information received or the current information and the voltage information received, whether to send a trip signal to an execution mechanism, wherein
• upon a current flowing from the main grid to the nano grid, the current is determined to be a forward current;
• and
• upon a current flowing from the nano grid to the main grid, the current is determined to be a reverse current,
• wherein the determining includes, upon the current direction being a reverse direction and upon the current being greater than a reverse current threshold, determining whether to send the trip signal, and upon the reverse current being continuously greater than the reverse current threshold within a delayed time period, sending the trip signal.