In this book, the main types of extracting harmonic devices are studied. Also, a method for extraction and measurement of harmonic components in the signal strength is introduced. The proposed method is based on parallel structure adaptive notch filter (ANF). A special algorithm for power systems is introduced which is presented simple mechanism to track fundamental frequency and amplitudes of harmonic components. Adaptive feature of proposed method provides tracking ability of power signals features variations like frequency, and fundamental and harmonic amplitudes. Simulation results is confirmed the desirable transient and steady-state performances of the proposed method.