Local linear approximation for tracking frequency in power systems

In this paper, we present an application of the local linear approximation technique in tracking power system frequency. Samples of the voltage phase angle are fitted using linear function. This approximation is valid locally on the left-sided window with variable length. The window slides with each new sample. The linear coefficient of the locally fitted function is the point estimate of the frequency deviation from the nominal value. For each new sample this technique automatically selects optimal window length in order to maximize estimation accuracy. A long window is selected if the frequency is slow varying, to increase efficiency in filtering noise and harmonics. For a fast varying frequency the window length automatically reduces in order to make frequency tracking more accurate but sacrificing on filtering efficiency. Automatic selection of the optimal window length that balances between tracking and filtering performance makes this technique very powerful in tracking frequency in a wider range, as required in generator control and protection applications. The paper concludes with the presentation of the representative simulation results.