Voltage difference envelope line-based harbor ship shore power connection system and method

The invention discloses a voltage difference envelope line-based harbor ship shore power connection system. The system comprises a shore power transformer, a first switch, a voltage difference envelope line detection apparatus and a control assembly; the shore power transformer is connected to ship power through the first switch; the voltage difference envelope line detection apparatus is connected with the first switch in parallel and converts an obtained voltage difference envelope line signal between shore power and ship power into a periodical positive pulsation signal to transmit to the control assembly; the control assembly takes the lowest point of the periodical positive pulsation signal as a datum point, T time is taken before and after the datum point separately, and the 2T timeis set to be a butt joint time frame; a switch-on signal is transmitted to the first switch within the butt joint time frame to control the first switch to be switched on; and shore power is connectedthrough the shore power t