Active power filter is a comprehensive solution to comprehensively solve power quality problems such as power grid harmonics, reactive power, and three-phase load imbalance. It is connected in parallel to the power grid to detect the harmonics in the power grid in real time and generate phase phase through the converter. The compensation current can dynamically filter out the harmonics in the power grid. The operation is not affected by the grid structure and load type, and will not resonate with the system, which perfectly realizes the harmonic control of various loads. It can also realize dynamic reactive power compensation and control capacitor switching to improve the power factor of the grid. At the same time, it also has the function of controlling the three-phase load current imbalance, and comprehensively solving various power quality problems encountered by the power grid.