Active power filter is used to suppress dynamic harmonic and compensate reactive power. It can compensate the various harmonic and reactive power which can overcome the disadvantages of LC filter such as harmonic suppression and reactive power compensation.

Recently, the number of arc furnace, electrified railway, rectifier, computer and printer, etc equipments in distribution network increases. The non-linearity, impact and unbalanced features contaminate the power quality. In other hand, the modern industry, commercial and residential users are sensitive to the power quality and require highly in it.

The traditional active power filter has low cost, simple structure and convenient maintenance, etc features to be applied widely. It is the main method to suppress system harmonic and compensate reactive power. But the large dimension and filter effect are related with the running situation. In certain situation, the active power filter vibrates with the system. As a result, the past active power filter management technology cant meet the requirements.