You want to use stranded THHN wire. Put it in conduit from the breaker panel to the machine, I like plastic conduit. Bring in a ground (green wire) from the breaker panel along with the power wires, do not ground with a rod through the concrete, your breaker panel should have a ground bus in it. The ground wire can be 1 size smaller (#10) than the power wires. If your breaker panel does not have a proper ground, then fix that first, consult an electrician for local codes.
As an alternative, you could use SO cable (black 3 conductor cable, like a heavy extension cord), but that is not the best practice and it's expensive.