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 effectiveness of classical passive filter compensation and active compensation must be considered. In high-voltage, high-power applications hybrid filter systems arc technically justilicd and cost-effective solutions. Hybrid filter control strategies succcssfiilly employed in the compensation of high-power rectifier loads based on tlie detection of the total current distortion are less effective in thc compensation of interharmonics. A frequency selective control system for a voltage controlled active lilter connected to the power system through a inultistagc passive filter is described. A bank of second-order ITR digital filters with interhaiinoiiic tracking ability is employed 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 cycloconvertcr load. Different control strategies based on the selective control system are investigated and compared with an earlier strategy based on the detcction of the total current distortion. By using individual detection and compensation of critical harmonics and intcrharmonics, hybrid power filters can be optimised to satisfy the distortion limits with the lowest active filter rating and switching frequcncy.