HVDC Back-to-Back System Configuration: Explained

[DUET]

The above diagram is for HVDC back to back system. My question is why do we call it back to back system?

Could someone please help me here?

 

[UltrafastPED]

It's a sports metaphor - like two games, back to back.

In this case it is because you see an AC system connected at one end, and another at the other end: back to back.

 

[DUET]

like two games, back to back.

Could you please explain it? I am guessing "the two games happening immediately one after another. Correct?"

 

[dlgoff]

http://www.thefreedictionary.com/back-to-back

 

[DUET]

The simplest configuration is the back-to-back interconnection in which two converters are on the
same site without a transmission line.

Could someone please indicate the similarity between the bold part of the above sentence and the HVDC back-to-back system diagram above?