Impedance-model-based stability analysis of DC microgrid

In DC microgrid, it is common that constant power loads (CPLs) exhibit negative impedance characteristics, which degrades the stability margin of the whole system. This paper focuses on the stability problem of isolated DC microgrid with multiple DC voltage control units and constant power loads. Taking controllers into account, the detailed impedance model of DC microgrid is established, and it shows the interaction between converters through analyzing the minor loop gain by using Nyquist criterion. Meanwhile, resonance is examined using impedance model. Impedances-based stability analysis reveals the influence of different factors on the stability, such as the size of the CPLs and the droop coefficient. To verify the analysis results, the simulation model is built based on PSCAD/EMTDC. The simulation results confirm the validity of the method. With the developed dc impedance and stability analysis method, the DC microgrid system stability characteristics can be evaluated, which can be used for system design to maintain stability.