In back-to-back converter systems used with doubly-fed induction generators (DFIG), rotor-side converter (RSC) and grid-side converter (GSC) generate fundamentally different harmonic spectra due to the distinct impedances they operate against. The machine’s inherent inductance naturally attenuates the RSC spectrum, whereas the GSC relies on an LCL filter designed around a fixed switching frequency to meet grid-code requirements. This asymmetry motivates using different switching strategies for the two converters: the GSC maintains a fixed frequency based on filter design, while the RSC can be tuned for improved efficiency.

In this study, the switching frequency of the generator-side converter is reduced from 3000 Hz to 2000 Hz to lower switching losses. However, this reduction increases harmonic distortion, particularly in frequency regions where filtering is less effective.

To mitigate the resulting harmonic content, a sinusoidal periodic carrier frequency (PCF) modulation technique is introduced. This method imposes a controlled wobble on the carrier frequency over time. While PCF modulation helps distribute harmonics across the spectrum, it may inadvertently increase low-frequency harmonic energy, where filtering is inherently weaker.

To overcome this limitation, the proposed method leverages resonant interactions between sideband harmonics generated by the PCF effect and those intrinsic to space vector modulation (SVM). By selecting PCF frequencies that are integer multiples of the fundamental frequency, the harmonic spectrum can be shaped more advantageously. The key innovation lies in the resonant synchronization of the PCF frequency at six times the fundamental frequency, with precise phase alignment to the base waveform. This configuration effectively redirects harmonic energy away from the critical low-frequency region and into higher-frequency bands, which are more amenable to attenuation by the generator’s natural inductance.

The study is based on original simulation models and spectral analysis of a 6 MW DFIG system. Multiple PCF parameters, including peak carrier-frequency deviation and phase angle, were tested to identify optimal conditions for harmonic redistribution. Initial simulations at a 2000 Hz switching frequency without PCF revealed severe harmonic violations, with grid-side transformer current magnitudes reaching 240 percent of grid-code limits. Conventional PCF modulation proved insufficient, as harmonic energy remained concentrated in low-frequency bands with inadequate filtering.

In contrast, the proposed resonant PCF–SVM approach successfully redistributed harmonic energy into higher-frequency regions, resulting in full compliance with grid standards at 93 percent of the allowable limit. The results demonstrate that this technique maintains current waveforms within harmonic limits even at reduced switching frequencies. Its straightforward implementation makes it highly practical for enhancing converter performance in large-scale wind energy applications.