A Comparison of Stability Analysis of Constant Power Load with Detailed Model in DC Microgrids

Abstract

The cascade connection of converters can have destabilizing effects on the response of the system due to the behavior of controlled converters as constant power load (CPL). It is prevailing to simplify the point-of-load (POL) converters as CPLs. The CPL simplification is a low-frequency approximation that assumes that there are no dynamic interactions between interconnected converters. However, the dynamic interaction between converters is another source of instability that must be taken into account. Furthermore, the dynamic interaction between converters can be very sensitive to parasitic elements within the converters; hence the results in real applications can differ substantially from analytical estimations. As a result, studying of detailed models can bring about a better understanding of stability analysis. In order to cope with these phenomena, the most accurate result comes from black-box models of the converters around different operating points obtained by the injection of perturbations to the actual converters and the application of identification tools. This black-box model result is equivalent to the averaged analytical model but it is able to account for the actual values of the parasitic elements. This paper compares the performance of the stability analysis with a CPL approximation with a detailed model of the POL converter. Moreover, the sensitivity of parasitic elements of the POL converter will be exposed.