Enhancing waveform distortion assessment in modern power systems: Key innovations for next-generation emission compliance

The increasing penetration of Distributed Energy Resources in modern power grids requires more advanced power quality analysis. In particular, waveform distortions must be assessed against established emission limits. To address this challenge, this paper introduces two key innovations to the widely adopted CIGRE/CIRED C4.109 harmonic compliance assessment methodology, which requires both the magnitude and phase angle of spectral components. The first contribution extends the spectral range beyond traditional harmonics to include supraharmonics in the 2–150 kHz band. Since analyzing such a wide spectrum requires high accuracy, particularly for amplitude and phase estimation, cosine windows are implemented within an Interpolated Discrete Fourier Transform framework. This approach replaces the standard DFT recommended by IEC 61000-4-7 and IEC 61000-4-30, effectively reducing spectral leakage. The second innovation consists in evaluating phase angles before grouping, within each consecutive 10/12-cycle window. This refinement improves accuracy in the characterization of spectral components relevant to compliance assessment. The proposed method is quantitatively validated against synthetic ground-truth signals over the 2–150 kHz range. A laboratory application on an emulated low-voltage network is also presented, with detailed experimental comparisons for representative components up to approximately 40 kHz. Results show that both the processing sequence and the spectral estimation method have a non-negligible impact on the 95th-percentile emission indices. The implementation and extensive validation of a custom test network represent a further contribution of this work and support a more robust and frequency-selective framework for emission compliance in modern power systems.