Control of a super-capacitor energy storage system to mimic inertia and transient response improvement of a direct current micro-grid

In dc microgrids (dc MGs), the dc link capacitor is very small to provide the inherent inertial. As a result, large voltage deviations occur during load changes or uncertain fluctuations from the fluctuated power resources. This leads to degradation of voltage quality. To overcome the low inertia problem, this paper proposes a fast-responding energy storage system such as supercapacitor can mimic inertial responses through some specified control algorithm. A bidirectional dc-dc converter is used for interfacing supercapacitor energy storage to a dc MG. The proposed control scheme is composed of a virtual capacitor and a virtual conductance. It is implemented in the inner loop controls, i.e. current loop control to be fast enough emulating inertia and damping concept. In order to study the stability of dc MG, 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.