A Duke Energy Corp. subsidiary for North Carolina electric customers has asked state regulators to let it raise residential rates by 16.6% in the coming months largely to recover their fuel costs, particularly natural gas. Duke Energy Carolinas serves customers in western and central North Carolina, including Charlotte, Durham and the Triad. Its annual fuel filing Tuesday with the state Utilities Commission also would raise industrial and commercial rates by double-digit percentages as well. Duke Energy Progress will make its annual fuel filing in June.