A Study Of The Influence Of Active Power Filter On Load

The rapid development of power electronics technology brings a lot of convenience to the transformation and application on power electronics, but it also brings the power system serious problems of power quality. Active Power Filter (APF) is the most effective methods to improve power quality. It has been and will still be a research hotspot in the application of power electronics. Unfortunately, in practical engineering applications, the amplification of load harmonic current occurs when APF is put into use. However, when APF is used to reduce the harmonics, the major concerns of harmonic control are harmonic improvement of grid side, and the load harmonic current changes of the load side get less attention. Aiming at this problem, the three-phase uncontrolled rectifier is taken as a non-linear load for study in this thesis.In this thesis, in order to prove the existence of the problems that the load harmonic current is larger after using the active power filter in practical application, a simulation mode of APF with the load of uncontrolled rectifier equipment, based on PSCAD platform, is established firstly. Furthermore, this thesis also analyses what are the possible causes of the changes of the load harmonic current. And then, a theoretical analysis of load harmonic current of uncontrolled rectifier is presented to provide the relationship between load harmonic current distortion and harmonic voltage distortion. Meanwhile, the variation of load harmonic current distortion with voltage distortion rate is obtained. Finally, by means of MATLAB simulation, the theoretical analysis conclusions are verified. And the reason of the amplification of load harmonic current distortion is found, which is due to the change of the harmonic voltage distortion when using APF.