In dc microgrids, the distributed sources and loads with different electrical characteristics are typically interconnected to the main bus through power electronic converters. The existence of interfaced converters creates two major problems: 1) the load-side converters and their associated loads, usually considered as constant power loads (CPLs), introduce destabilizing effects into the system; 2) the source-side converters do not possess any inertia or damping properties but reduce the overall inertia of the system. To overcome the stability problems caused by CPLs and low inertia, this paper proposes an active damping strategy based on a linear feedback. The proposed strategy measures the inductor current implemented in source-side boost converter in order to enhance the damping of the dc microgrids with CPLs. The control input-to-output voltage transfer function of a boost converter loaded with a CPL is inherently nonlinear, unstable and a non-minimum phase system that makes its control very difficult. In addition, the synthetic inertia of dc bus is enhanced by adding the virtual inertia control to the inner current control loop that is fast enough to emulate inertia and damping coefficient concept. In order to study the stability of dc MG with CPLs, a comprehensive small-signal model is derived and then, an acceptable range of inertia response parameters is determined by using the system’s root locus analysis. Performance of the proposed control structure is demonstrated through numerical simulations.
