Stability analysis of active harmonic filter in presence of power factor correction capacitors

In order to make the load compensators cost effective, Active Harmonic Filters (AHF) are used in conjunction with Power Factor Correction (PFC) capacitors, so that the load harmonics are compensated by AHF and the reactive power requirement of the load is supplied by the PFC capacitors. However, presence of PFC capacitors in association with the short circuit impedance of the source strongly influences the compensation behavior of the AHF. This paper evaluates the performance of AHF wherein it operates in presence of PFC capacitors. A rigorous analysis of the system is presented and it is objectively shown that under what conditions the system fails to compensate for the load harmonics. A laboratory prototype of the proposed AHF having an rms current rating of 50 A has been developed. Detailed experimental studies are carried out utilizing the prototype to verify the instability problem.