Active Power Decoupling in Cascaded H-Bridge Converter Using Secondary-Stage Isolated DC-DC Converters

Due to power imbalance of each leg of a three-phase cascaded H-bridge (CHB) converter, a double-line frequency ripple (DLFR) originates on the DC-link capacitors of each CHB module. To rectify this issue of DLFR, bulky high-valued electrolytic DC-link capacitors are employed in each CHB module. An alternate solution is to use an active power decoupling (APD) circuit at DC-link of each sub-module. However, using APD circuit in each CHB module results in increased system complexity and switch-count. In this context, this paper proposes an integrated-isolated DC-DC (IID) converter, which acts a secondary-stage for the CHB converter and performs APD operation, while maintaining desired output power without using additional switches. Each IID converter based conversion-chain connected with CHB module has the ability to transfer DLFR to the decoupling capacitor. Furthermore. the control of presented IID based CHB along with possible modes of operation are discussed in the paper. Additionally, the validity and effectiveness of IID based CHB converter along with its control are verified by simulation results.