HVDC Transmisson

Hi all,
I need you guy's help again.
I have a project to design a high voltage DC transmission system and the power rating is 10MW.
I found some circuit diagram from google, but i don't understand it.
A prototype diagram is attached as below.
Th problem is I don't know why the current flow through the inductor the both terminal is possitive, Is it something related to the inductor's formula V = L(di/dt) ?
and how about the firing angle, is it used to shift the waveform from sine wave to cosine wave? or used to change the AC to DC?
The last question is I required to build a voltage sharing circuit for the series connected SCRs, can anyone show me how to design it? please......

I'd like to see the waveforms for this circuit.

3φ AC is chopped up, sent through an inductor that boosts the voltage slightly due to L ΔI/ΔT and then "decoded" at the receiving end.

I don't see why you can't have just a 6 diode bridge at one end or the other, rather than SCRs at both ends.

The current sharing might be done by using skinny wires to connect the SCRs, so it doen't show up on a schematic.

You have some links that explain this novel circuitry?
You have a value for the inductor?

I'm glad that this is a school project.
The SCRs on the left convert to AC to pulsating DC. This gives a positive output with no polarity reversal. The inductor acts as a choke and may just represent the line inductance. That's why you see + on both sides of it. The SCRs on the right then chop the DC back into AC.