I. Introduction
Since the 1970s, due to the rapid development of power electronics technology, various power electronic devices have been widely used in power systems, industries, transportation, and household appliances, and the harm caused by harmonics has also become increasingly severe [1] [2]. Countries around the world have given full attention to the issue of harmonics. Many countries and international academic organizations have formulated standards and regulations to limit harmonics in power systems and electronic equipment [3]. Taking electronic audio equipment as an example, Total harmonic distortion (THD) refers to the extra harmonic component of the output signal caused by a Nonlinear element when the audio signal source passes through the power amplifier [4].