Sounds like a Jerusalem artichoke to me. The root is a light brown tuber with little knobs, and looking very much like ginger on the outside. The flesh, though, is quite potato-like.
The plant itself is a thick, tall, tough stalk that produces nasty burrs after flowering. I used to get them caught in my hair when I went to pull them up and get their yummy roots. If you pile the stalks up to dry when you're done with them, they make good kindling for a bonfire.
I used to have them lining the edge of my property in Vermont (they grew there like weeds, I mean to say). They were an early Spring, Northern climate delicacy in the wild. Edible weeds can be so yummy!
I would scrub them gently and just boil or steam until soft...less time than w/ potatoes, as I recall. I can't imagine a better way to eat them than with butter, salt and pepper. Delicious. I hope this is what you have in your yard.