Abstract: A system and method are provided for enabling multi-functional support of an extant synchronous alternating current (AC) grid. At least one extant electricity source and at least one extant electricity sink are connected by two or more high-voltage direct current (HVDC) transmission circuits connected in turn in series with each other with at least one pair of HVDC circuits interconnected through an intervening high-voltage AC (HVAC) point of interconnection. One or more of the HVDC transmission circuits includes a 2-terminal or a multi-terminal transmission link. A 2-terminal HVDC circuit is dedicated to connecting with the electricity sources and sinks.