Research On Active Power Filter

Harmonic pollution and deficiency of reactive power worsen power quality of powersystem, so as a dynamic harmonic suppression and reactive power compensation device,active power filter is being paid more and more attention to by scholars in the field of electricpower.Base on that, this paper carries out a study on active power filter.Firstly, the detection methods based on instantaneous reactive power theory are deeplystudied and analyzed. When the phase of grid voltage is asymmetry and it is necessary todetect both harmonic and reactive power, reactive current detected by the d qmethod will bedeviation because of the phase angle difference of between the sin-cosine signal extracted byphase-locked loop and the desired signal. Therefore, the improved d qdetection method isproposed in the article, which uses the fundamental positive sequence voltage phase angle andthe fundamental positive-sequence active current frequency to calculate sine-cosineinformation applied to dq coordinate transformation. Thus, that forms a closed loop systemto eliminate the effect of phase asymmetry of grid voltage. The accuracy of the improvedmethod is verified by simulation results of MATLAB/SIMULIK.Secondly, based on discrete mathematical model of two phases DC function of shuntactive power filter, the control strategy of compensation current is researched. To directlyreplace the next moment compensation current with the current moment instruction current inspace vector modulation method, the deficiency of lagging behind one beat is inevitable.Therefore, the inner current loop deadbeat control strategy based on voltage space vector isapplied to control active power filter since the next moment instruction current is replacedwith the next moment compensation current in the control strategy. Thus, that makes up theshortage of lagging behind one beat and improves the real-time performance of active powerfilter.Lastly, the article designs shunt active power filter combining with engineering practice.The overall simulation model is built to confirm that no matter the grid voltage is symmetricalor not, the distorted current can be accurately detected by the improved d qdetection andthe real-time tracking compensation performance of SAPF can be guaranteed by the currentinner loop deadbeat control based on voltage space vector. All in all, after the harmonic wavesare restrained and reactive power is compensated by active power filter the total harmonicdistortion rate of grid current of power system with nonlinear loads is decreased obviouslyand the power quality of the system is improved.