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An algorithm based on the concept of adaptive notch filter (ANF) is proposed for estimation of power system frequency. The ANF is a second-order notch filter that is further furnished with a nonlinear differential equation to update the frequency. The method permits direct estimation of frequency and its rate of change for a power system signal. The performance of the algorithm is compared with that of a newly introduced algorithm, which is based on using an enhanced phase-locked loop (PLL) system. Unlike the PLL-based frequency estimator, the proposed algorithm does not employ a voltage-controlled oscillator. This makes its structure much simpler for implementation. The transient response of the proposed estimator is faster than that of the PLL-based estimator. Computer simulations are presented to highlight the usefulness of this approach in estimating near-nominal and off-nominal power system frequencies.