A method of reducing THD can include: acquiring a first average inductor current during a first conduction time of a main power transistor of a power converter in a switching cycle; acquiring a second average inductor current during a second conduction time and an off time of the main power transistor in the switching cycle; and adjusting the second conduction time of the main power transistor in accordance with a difference between the first and second average inductor currents, where the first and second conduction times are successive.