Sift together flour, baking powder, and salt in a medium mixing bowl. Combine sweet potatoes, shortening, and sugar; mix well. Cut into dry ingredients with a pastry blender until well blended.
Turn dough out onto a lightly floured surface, and knead 4 to 5 times.
Roll dough to 1/2-inch thickness; cut with a 2-inch biscuit cutter. Place biscuits on greased baking sheets. Bake at 425° for 15 minutes or until lightly browned. Remove from baking sheets, and serve warm.