Abstract
This article provides formulae to determine the root mean square (rms) value of a capacitor current in an inductive-capacitive-inductive (LCL) filter used in a parallel active power filter (PAPF) circuit. The article presents an analysis of three components of the capacitor current: a component forced by the usually distorted voltage of the grid; a component forced by the nonlinear load current harmonics and harmonics in the output current of the PAPF that compensates them (a novel aspect presented in this document); and a component forced by the inverters of the PAPF containing carrier and sideband harmonics. The article also presents formulae for determining the rms value of current harmonics in dc-link capacitors forced by the ripple of the ac output current without load of the filter inverters (also novel to this document). The results of the analysis have been confirmed by simulation and experimental research of a commercial active filter consisting of two parallel interleaved voltage inverters. Elements of the LCL filter of the PAPF have been selected according to dependencies available in scientific and technical literature. In addition, the formulae presented in the article are used to verify the correctness of selection of capacitors from the point of view of their catalogue acceptable rms value of capacitor current.
Highlights
The parallel active power filter (PAPF) contains three groups of passive power elements: dc-link capacitors, inductances, and capacitors in the LCL-ripple filter
The analysis presented in these works, applied to the PAPF system with the deactivated reactive power compensation for the basic harmonic, will not reveal the harmonic values determined in this article, even if it takes into account the 5, 7, 11, and 13-order ac harmonic in the output current
In order to verify the correctness of the analysis of components of the currents of the LCL-ripple filter capacitor and inductors, studies were conducted with the FAS-400k-400 and FA3-100k-400 active filters produced by the MEDCOM company based in Warsaw Jutrzenki 78A str., Poland
Summary
The parallel active power filter (PAPF) contains three groups of passive power elements: dc-link capacitors, inductances, and capacitors in the LCL-ripple filter. This article presents an analysis leading to the determination of the rms current of LCL-ripple filter capacitors used at the output of the PAPF. Many articles publish theoretical analysis and results of simulation and experimental tests of current components in LCL filter capacitors and dc-link circuit. They do not provide dependencies which can be used to calculate the rms values of currents in these capacitors. This article gives simplified equations with an error of about 10% on the basis of which one can determine both the rms value of the capacitor current in the dc-link circuit and the three current components of the LCL filter capacitor.
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