Input Impedance Analysis and Hybrid Filter Design of Dual Active Bridge Converter Connected to Line-interactive Inverter

Abstract

Based on extra element theorem (EET), the impedance influence between a line-interactive inverter and a dc-dc dual active bridge (DAB) converter is analyzed to understand the affection of the stability and dynamics degradations. The dc-dc power converter operates as the constant power load (CPL) which has a negative resistance feature at the low-frequency region. At this region, the dc-dc converter becomes unstable when the impedances of the inverter and the dc-dc converter are overlapped. In addition, the controller performance of the dc-dc converter can be degraded when the impedance interaction occurs at other frequency regions. Therefore, it is required to prevent this impedance overlap for the entire system stability. Each impedance of the line-interactive inverter and the DAB converter is analyzed, respectively. Based on this analysis, an effective hybrid filter design for the DAB converter is proposed. The impedance influence is verified by empirical and experimental results with a 3.3 kW DAB converter and a 3.3 kW line-interactive inverter prototype.