System Defense (SEV)
From what I have found by playing the game non-stop, by researching the "Base" technology in the "research panel". Once you have access to the largest that you can build fill it with armour on all of the armour points and have shields of both types "Phase Shields" and "Plain shields" four of each, and fill it with powerful weapons. This all seems expensive so make sure you have a very good resource income, also make sure you have the "Quantum Generator" on it as well and have extra space for supplies that the generator creates. You need the "Quantum Generator" because "Lasers Weapons" use supplies to fire and so this way it will never run out of ammo. After you have all this done you will need a "Base Ship" with the ability to build other ships so it will need a ship yard on it. This will also need Quantum Generators and a large supply storage ability this will allow it to build the "Large Base" from the beginning of this explanation, now with the "Base Ship" built move it over a worm hole and build one base then move to the next worm hole. I have found this method to be the best one to defend an entire system. Using this method I have survived over 500 turns under attack from over 6 directions using six powerful and defended "large bases" over each worm hole.
The results will depend on how well you have made your bases.