Low-frequency Stability Analysis of the DC-link in Dual Active Bridge (DAB) Based Microgrid

A micro-grid system based on a source dual active bridge (DAB) converter connected with load buck-boost DC/DC converter and DC/AC converter by the common DC-link is studied in this paper, which is widely investigated in the yield of intelligent distribution microgrid. As the power transmission hub, the stability of the DC-link voltage plays a key role in the normal operation of the whole system, which affects the stable operation of the back-stage inverters as well as the normal power supply of connected loads. The stability problem in DC-link may occur at the low frequency, if the impedance characteristic of DAB as a source is incompatible with the impedance characteristic of back-stage converters, which will be investigated in this paper. Seen from common DC-link, the impedance of DAB, DC/DC and DC/AC converters on this side are modeled. Based on the model, the mechanism and main contributor of low-frequency oscillation in DC-link are presented. The derived impedance model in the frequency domain and the result of stability analysis are verified by the simulation.