Frequency Design of Three-phase Active Front-End Converter with Reduced Filter in EV Chargers

Abstract

In recent years, significant research and adoption of periodic variable-switching frequency pulsewidth modulation (PWM) (P-VSFPWM) have been observed in ac/dc voltage source converters (VSCs). This technique aims to reduce ripple in ac inductor current and dc capacitor voltage, suppress injected current harmonic amplitudes for electromagnetic compatibility (EMC) compliance, and minimize switching losses. However, the presence of overlapped harmonic spectra from different switching harmonic bands can lead to heightened harmonic magnitudes due to the wide-frequency variation, necessitating additional filtering measures. Surprisingly, there is notable absence of harmonic spectra analysis under P-VSFPWM, despite the growing concern over supraharmonics (2-150 kHz) emission injected to the grid from the electric-vehicle (EV) chargers. To address this gap, this article proposes the interleaved P-VSFPWM to mitigate harmonics overlap without deviating from the intended purpose of P-VSFPWM. A fast-acquisition supraharmonics model under arbitrary P-VSFPWM has been proposed based on vectorization, facilitating the subsequent filter design process. Furthermore, this study identifies the optimal P-VSFPWM profile with minimal required filtering inductance based on the spectra analysis. These findings are verified by PLECS simulations and experimental results.