Hybrid filter control system with adaptive filters for selective elimination of harmonics and interharmonics

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.