Comparative analysis of three-level dual active bridge DC-DC converter between reflux-power-optimised and current-stressoptimised phase shift control

Abstract

The reflux power and current stress of three-level dual active bridge (3L-DAB) become very large under the conventional phase shift (CPS) control, especially when the voltage conversion ratio is unequal to one or working with light load. To improve the performance, reflux-power-optimised (RPO) and current-stress-optimised (CSO) have been investigated in many literatures. However, the current stress variation with RPO control, the reflux power variation with CSO control, and the relations between the two optimal strategies have not been decided yet. Thus, a detailed comparative analysis is presented in this study. The operation principle of 3L-DAB under CPS, RPO and CSO control strategies is briefly described. The reflux power and current stress comparison among the three strategies is performed within different ranges of transmission power and voltage conversion ratio. The RPO and CSO control strategies are approximately equivalent when the voltage conversion ratio is less than 1/4, and they can minimise the reflux power as well as the current stress in the whole power range. An experimental prototype was developed to verify the correctness of the theoretical analysis.