Performance of Demodulation-Based Frequency Measurement Algorithms Used in Typical PMUs

TLDR

Amplitude measurement performance under interference can be determined directly from filter frequency responses, as the error from a single tone is computed via the cascade algorithm’s magnitude response. The paper proposes methods to evaluate and predict the worst‑case error of demodulation‑based frequency measurement algorithms when subjected to sinusoidal interference. The authors derive an error‑prediction formula that guides the selection of output filters to achieve specified performance in such algorithms. The method has been successfully applied to design frequency measurement algorithms used in Hydro‑Que/spl acute/bec’s special protection schemes.

Abstract

This paper presents a method for evaluating the performance of demodulation-based frequency measurement algorithms in the presence of additive interfering sinusoids. Determination of the performance of amplitude measurement schemes under such conditions is straightforward once the frequency responses of the filters involved in the process are known, since the error induced by a single interfering tone is easily computed using the cascade algorithm's frequency response magnitude. This paper presents a similar method for predicting the worst error of frequency measurement schemes with respect to sinusoidal interference. Once acquainted with the proposed error prediction formula, the only difficulty in designing effective frequency measurement algorithms is the appropriate selection of output filters to achieve the specified performance. The method has been used successfully in designing frequency measurement algorithms currently used in Hydro-Que/spl acute/bec's special protection schemes.