Active Power Filter (APF) is a new type of power electronic device used for dynamic suppression of harmonics and compensation of reactive power. It can compensate for harmonics and reactive power that vary in size and frequency. The reason why an active filter is called active, as the name suggests, is that the device needs to provide a power supply (to compensate for the harmonics of the main circuit). Its application can overcome the shortcomings of traditional harmonic suppression and reactive power compensation methods such as LC filters (which can only be fixed compensation), achieve dynamic tracking compensation, and can compensate for both harmonics and reactive power.