Feedforward-Based Variable Frequency Second Harmonic Current Suppression Strategy for Cascaded H-Bridge Energy Storage Converter

The second harmonic current (SHC) is significant in the cascaded H-bridge converter with dc–dc stage and supercapacitor under high current and variable output frequency, increasing the risk of overcurrent in the dc–dc. Conventional suppression strategies designed for fixed-frequency SHC constrain the dc–dc controller bandwidth to the SHC frequency, inevitably degrading dynamic performance. To address this issue, this article proposes a feedforward-based SHC suppression strategy. By analyzing the transmission path of SHC, an accurate feed-forward compensation is introduced at the dc voltage reference point, blocking the second harmonic signal from entering the dc–dc control loop. This decouples the SHC suppression strategy from the controller, eliminating the bandwidth constraint imposed by the SHC frequency. Therefore, the proposed strategy ensures both effective SHC suppression and enhanced dynamic performance under variable frequency conditions. Furthermore, the dc–dc controller design process is significantly simplified. Finally, the experimental results validate the effectiveness of the proposed SHC suppression strategy.