D. Basic et al., Hybrid filter control system with adaptive filters for selective elimination of harmonics and interharmonics, IEE P-EL PO, 147(4), 2000, pp. 295-303
The interharmonics produced by some classes of nonlinear loads limit the ef
fectiveness of classical passive filter compensation and active compensatio
n must be considered. In high-voltage, high-power applications hybrid filte
r systems are technically justified and cost-effective solutions. Hybrid fi
lter control strategies successfully employed in the compensation of high-p
ower rectifier loads based on the detection of the total current distortion
are less effective in the compensation of interharmonics. A frequency sele
ctive control system for a voltage controlled active filter connected to th
e power system through a multistage passive filter is described. A bank of
second-order IIR digital filters with interharmonic tracking ability is emp
loyed for high-resolution spectral estimation and control. This approach is
verified by simulation. It is shown for example that the active filter can
compensate for supply interharmonics produced by a cycloconverter load. Di
fferent control strategies based on the selective control system are invest
igated and compared with an earlier strategy based on the detection of the
total current distortion, By using individual detection and compensation of
critical harmonics and interharmonics, hybrid power filters can be optimis
ed to satisfy the distortion limits with the lowest active filter rating an
d switching frequency.