Low-Frequency Resonance Suppression of a Dual-Active-Bridge DC/DC converter Enabled DC Microgrid

In this paper, the small signal stability issue of a dual-active-bridge (DAB) converter enabled dc microgrid is addressed. The derived impedance characteristic of the source DAB converter reveal that the stability of this dc grid is decided by the low-frequency terminal behaviors of integrated units, which is different from that of dc microgrids powered by other types of source converters. At this low-frequency range, the tightly regulated load converter exhibits constant power load behavior even with a low control bandwidth, which degrades system stability by exacerbating interactions among power converters. Moreover, the deployed power management strategy requires operating mode transitions of energy storage units to achieve intelligent power flow, which further complicates system impedance characteristics. To analyze and solve these issues, the systematic impedance models of this dc grid under different operation modes are derived and analyzed. Reduced-order low-frequency models are simplified from the systematic impedance model to unravel the resonance mechanism. In addition, an impedance shaping technique is proposed to eliminate the resonant path in the reduced-order low-frequency models, therefore the dc grid stability has been improved. Finally, a hardware-in-the-loop application with OPAL-RT real-time simulators is used to validate proposed methods.