Performance assessment of two active power filter control strategies in   the presence of non-stationary currents
  This paper describes an active power filter (APF) control strategy, which eliminates harmonics and compensates reactive power in a three-phase four-wire power system supplying non-linear unbalanced loads in the presence of non-linear non-stationary currents. Empirical Mode Decomposition (EMD) technique developed as part of the Hilbert-Huang Transform (HHT) is used to singulate the harmonics and non-linear non stationary disturbances from the load currents. The control strategy for the APF is formulated by hybridizing the so called modified p-q theory with the EMD algorithm. A four-leg split-capacitor converter controlled by hysteresis band current controller is used as an APF. The results obtained are compared with those obtained with the conventional modified p-q theory, which does not possess current harmonics or distortions separation strategy, to validate its performance. 
Vin Cent Tai, Phen Chiak See, Marta Molinas, and Kjetil Uhlen
math.OC cs.SY