System interconnection device and method of designing same

A method of designing a system interconnection device comprising:

• unit parallel circuits, each including a rectifying element and a direct-current reactor connected in parallel;
• a serial circuit including a plurality of said unit parallel circuits serially connected such that total inductances of said direct-current reactors in positive and negative rectifying directions of said rectifying elements are substantially equal;
• and
• a circuit-breaker for connecting and disconnecting the two systems, wherein:
• said circuit-breaker and said serial circuit are interposed between the two systems;
• and
• a current attenuation time constant .tau. of said direct-current reactors is set according to the formula:
• .tau..ltoreq.T.sub.0 /ln (I.sub.DCMAX /I.sub.DC0)
• wherein I.sub.DC0 is a current flowing through said direct-current reactors during normal operation, I.sub.DCMAX is a maximum current during a current-limiting effect, and T.sub.0 is a disconnect/connect interval of said circuit-breaker, required for re-connection of the two systems;
• said method comprising the steps of:
• setting in advance a rated voltage and a rated current of said unit parallel circuits;
• setting a number of stages of said unit parallel circuits to be serially connected so as to be able to handle a voltage at least as large as the desired rated voltage;
• and setting a number of said serial circuits to be connected in parallel so as to be able to handle a current at least as large as the desired rated current.