Drum washing machine and method for cleaning tub thereof

A method of controlling a washing machine, wherein the washing machine comprises a tub and a drum rotatably supported in the tub, the method comprising:

• supplying wash water to the tub in a first water supply step while the drum is rotated at a water supply RPM;
• starting a first washing step after the first water supply step is complete, the first washing step comprising accelerating the rotating drum from the water supply RPM to a first washing RPM, wherein the rotational force of the drum and a frictional force between the wash water and the rotating drum causes the wash water to form a circulating water current along an inner circumferential surface of the tub and an outer circumferential surface of the drum, lifting the wash water from a lower part of the tub to an upper part of the tub, and washing the surfaces of the tub and the drum;
• and
• starting a wash water draining step during the first washing step, the wash water draining step comprising switching on a drainage pump to adjust an amount of the wash water held in the tub.