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In recent years, power quality has become a significant issue for both utilities and customers. Power quality issues (Arrillaga, Watson, & Chen, 2000; Bollen, 2000 ; Dugan, McGranaghan, & Beaty, 2000) and the resulting problems are the consequences of the increasing use of solid state switching devices, non-linear and power electronically switched loads, unbalanced power systems, lighting controls, computer and data processing equipment as well as industrial plant rectifiers and inverters. These electronic types of loads cause quasistatic harmonic dynamic voltage distortions, inrush, pulse type current phenomenon with excessive harmonics and high distortion. A power quality (PQ) problem usually involves a variation in the electric service voltage or current, such as voltage dips and fluctuations, momentary interruptions, harmonics and oscillatory transients causing failure or mal-operation of the power service equipment. In order to improve electric power quality, the sources and causes of such disturbances must be known before appropriate mitigating action can be taken. However, in order to determine the causes and sources of disturbances, one must have the ability to detect and localize these disturbances. Estimation of amplitude and phase of fundamental, as well as harmonic signals has been one of the important tasks in measurement, control, relaying protection, distribution automation, and intelligent instrumentation of power system. Accurate power fundamental frequency is a necessity to check the state of health of the power index, and a guarantee for accurate quantitative measurement of power parameters, such as voltages, currents, active power, reactive power, and energy, and so on, in multifunction power meters under steady states. It is more difficult to precisely estimate the fundamental frequency of power systems in presence of harmonics and noises than under sinusoidal condition. It is essential to seek and develop some effective algorithms for accurate estimation of the instantaneous fundamental frequency of power systems under non-sinusoidal conditions.