Active power filter, referred to as APF, is a new type of power electronic device used to dynamically suppress harmonics and compensate reactive power. It can control the harmonics with variable size and frequency in real time.  What is active? It is necessary to provide power supply to compensate the harmonic of the main circuit, which can overcome the defects of traditional filter in harmonic suppression, and realize dynamic real-time governance. At the same time, for example, the active power filter of Xidong electric appliance belongs to the parallel type, and the equipment has a self-protection mechanism. Even in case of emergency, it will not affect the production of customer enterprises.  The most important thing is that the active filter can filter out multiple and higher harmonics at the same time without causing resonance. According to the principle of different manufacturers to realize the inverse compensation signal, the materials used are different, the algorithm is different, and the real-time response time is indeed quite different.