Improvement of Indirect Harmonic Compensation Method Using Online Discrete Wavelet Transform ¤ Mehdi Fallah Department of Electrical Engineering, Sahand University of Technology, Tabriz, Iran m _ fallah@sut.ac.ir Javad Modarresi Department of Electrical Engineering, University of Isfahan, Isfahan, Iran j.modarresi@eng.ui.ac.ir Ali Ajami † Department of Electrical Engineering, Azarbaijan Shahid Madani University, Tabriz, Iran ajami@azaruniv.edu Mohammad Tavakoli Bina Faculty of Electrical Engineering, K. N. Toosi University of Technology, Tehran, Iran tavakoli@kntu.ac.ir Received 23 January 2015 Accepted 7 September 2015 Published 27 October 2015 This paper introduces a new method based on the ¯nite impulse response (FIR) ¯lter and inverse discrete wavelet transform (IDWT) in order to separate the fundamental component from the non-ideal load voltage. Then, the proposed method is applied to the single-phase shunt active power ¯lter. The presented simulation and experimental results show that in the sug- gested indirect method (IM), the compensation of the load current will continue correctly even under non-sinusoidal load terminal voltage. For this purpose the fundamental component of load terminal voltage is extracted by the new proposed method, and the second-order gener- alized integrator (SOGI) is used for improving the total harmonic distortion (THD) of the source side current. The operations of the proposed control method are con¯rmed by the *This paper was recommended by Regional Editor Tongquan Wei. † Corresponding author. Journal of Circuits, Systems, and Computers Vol. 25, No. 4 (2016) 1650019 (20 pages) # . c World Scienti¯c Publishing Company DOI: 10.1142/S0218126616500195 1650019-1