Low-Capacitance CHB-Based SST Based on Resonant Push–Pull Decoupling Channel

Cascaded H-bridge-based solid-state transformer (CHB-SST) has been the typical scheme in medium- and low-voltage ac/dc conversion applications, and large-size capacitance caused by second-order ripple of submodules (SMs) is the inherent problem of CHB-based systems. In this article, we propose a novel low-capacitance CHB-SST based on zero-impedance resonant push–pull (ZRPP) decoupling channel for ripple power. ZRPP presents zero-impedance characteristic at its switching frequency equaling to series resonant frequency, which makes the equivalent parallel of CHB ac-link capacitors, and provides a decoupling channel for ripple power. Therefore, the horizontal SMs ripple power can achieve mutual cancelation based on their own three-phase symmetry, which significantly reduces the size of ac-link capacitance. In addition, the elimination of SMs ripple-voltage achieves the elimination of grid zero-sequence harmonics from root cause, and the mutual clamping of parallel ac-link capacitors also achieves the voltages self-balancing, which reduces the complex of system control. The CHB-SST configuration, operating principle, ripple-power decoupling, SMs voltage self-balancing, system design, and evaluation are discussed in this article. Finally, the effectiveness of the proposed CHB-SST is verified by simulation and experiment.