Control method for the cascaded H-bridge converter using cascaded switching frequencies and voltage levels to minimize the high-frequency ripple-current

To facilitate the adoption of the cascaded H-bridge converter for applications demanding increased control bandwidth and a lower total harmonic distortion (THD), a novel control strategy is introduced. This strategy involves the utilization of higher switching frequencies and specific dc voltages, tailored individually for each cell. The proposed control strategy is mathematically derived and validated through simulation. The analysis demonstrates that the addition of each cell beyond the fundamental cell, doubles the frequency of the output voltage of the cascaded H-bridge while halving its amplitude. Together, this results in a fourfold reduction in the high-frequency ripple current in the filter inductor per added cell, which, in comparison with the current state-ofthe-art PWM control strategies, is doubled. As a result, the filter effort and volume is greatly reduced, giving rise to a more flexible trade-off between increasing control bandwidth and increased THD on one side and losses and volume on the other side.