A Novel Voltage Balancing Method of Cascaded H-bridge Multilevel Converter With Supercapacitors Energy Storage System for Capacitor Voltage Ripple Reduction

Cascaded H-bridge multilevel converter(CHBC) has become a highly attractive topology in high-voltage and large-capacity energy storage system(ESS). In a cascaded H-bridge multilevel energy storage converter(CHB-ESC), energy storage elements(ESEs) such as batteries and supercapacitors are distributed in each power sub-module(PM), and the energy balancing among the ESEs is of great importance. In a two-stage CHB-ESC, the voltage balancing of the DC-link capacitors and the energy balancing of the ESEs should be met simultaneously. Due to the limitation of the charging and discharging current of the ESEs, the large current on the AC side in high-power applications will cause large ripple on the voltage of the DC-link capacitor. In order to reduce the voltage ripple of the DC-link capacitor in the two-stage topology, this paper proposes a novel voltage balancing method of CHBC with supercapacitors ESS for capacitor voltage ripple reduction. The PMs rotation is realized by a multi-factor weight optimal sorting method based on the voltage value of the supercapacitors and the voltage value of the DC-link capacitors. While ensuring the voltage balancing among the supercapacitors of each PM, the voltage ripple of the DC-link capacitors can be effectively reduced. Finally, the effectiveness of the proposed method is verified by simulation results.