Studies On The Implementation Of Resistive Active Power Filter For Damping Background Harmonics

In power distribution systems, there are a lot of power electronic devices andnonlinear electric equipment, which inject large amounts of harmonics to the system whenthey are in operation. When the system parameters satisfy certain conditions, harmonicswill resonate during transmission, threatening the power supply electrical equipment ofthe system. In order to ensure the quality of power supply, it’s of great need to suppressharmonics. Installing shunt active power filter (APF) is an important approach to dampharmonics in the transmission line.This paper mainly deals with the problem of background harmonic amplification tocarry out relative tasks. The resistive active power filter (RAPF) based on voltagedetection can effectively suppress the amplification of background harmonics, which isproposed by H.Akagi etc. On condition that the characteristic impedance of thetransmission line is already known, the damping performance of background harmonics isbest when the virtual impedance of RAPF matches perfectly with the characteristicimpedance according to theoretical analysis. However, the experimental result does notagree with the theoretical analysis, because H.Akagi etc take RAPF as an ideal controlledcurrent source when performing theoretical analysis, without considering the negativeeffect of RAPF’s equivalent output impedance on the suppression of backgroundharmonics. In order to achieve the best harmonic damping performance, this paper makesa deep research on the accurate matching approach of RAPF’s virtual impedance.RAPF output impedance is closely related with its topological structure and controlscheme. The output impedance of RAPF with L type filter is relatively large, whoseinfluence on the system background harmonic is small, but its high frequency attenuationability is limited when damping specific background harmonics. As for LC and LCL typeRAPF, its high frequency attenuation capability is strong, but its output impedance isrelatively small in some frequency range under the regulating of PI controller, whoseeffect on the system should not be neglected. However, we can selectively amplify theRAPF output impedance of certain frequency band by shifting to a multiple proportionalresonant (PR) controller, which can make up for the disadvantages of LC and LCL type RAPF with PI controller. Therefore, this paper puts forward its optimized harmonicsuppression scheme based on resistive active power filter: modifying the virtualadmittance of RAPF according to the influence of RAPF output impedance; or selectingmultiple proportional resonant controller to enhance RAPF output impedance. Finally, inthis paper, simulation and experimental results are presented to verify the effectiveness oftheoretical analysis.