A power decoupling control method for the regenerative cascaded-H-bridge-based motor drive

The cascaded H-bridge (CHB)-based medium-high voltage motor drive suffers a severe 2nd-harmonic ripple power problem on the DC side, especially under low output frequency conditions. Currently, strategies to address this problem include increasing the DC capacitors or adopting active power-decoupling methods that require extra switches and passive components. This paper proposes a novel power decoupling control method for the regenerative cascaded multilevel motor drive converter. Considering the inherent balance of the ripple power in the three phases and the special topology of the regenerative CHB-based motor drive, this method induces a negative-sequence current with special frequency into the active front end of each power module to transfer the ripple power of all power modules into the core column of the input transformer, allowing them to counteract each other. In this way, the 2nd-harmonic ripple of the DC voltages are eliminated without the need for additional components or impacts on the input and output power quality, which can greatly decrease the requirement for DC capacitors.