Impact of Virtual Inertia on DC Grid Stability with Constant Power Loads

TL;DR

This paper analyzes how virtual inertia affects the stability of low-inertia DC grids with constant power loads, providing a stability criterion, optimal virtual inertia design, and validation through tests.

Contribution

It offers a rigorous stability analysis, a closed-form criterion, and guidelines for designing stable DC grids with virtual inertia in the presence of CPLs.

Findings

Virtual inertia can improve DC grid stability within certain limits.

Analytical expressions for optimal and maximum virtual inertia are derived.

Test results validate the stability analysis and design guidelines.

Abstract

Virtual inertia is an effective control approach to attenuate sudden voltage changes during transient events in low-inertia DC grids. While methods have been proposed to implement virtual inertia, its impact on DC grid stability in the presence of constant power loads (CPLs) remains unclear. In this paper, we perform a rigorous stability analysis for DC grids with CPLs powered by virtual-inertia-enhanced converters. We derive a closed-form stability criterion that can be used to evaluate the impact of virtual inertia on the system stability, and demonstrate that, given a set of system parameters, the stability of a DC grid powering CPLs can be improved for a range of virtual inertia designs. We provide analytical expressions for the optimal virtual inertia that improves stability and for the maximum virtual inertia that does not deteriorate stability. In addition, we present a step-by-step guideline to design a stable DC grid with virtual inertia. Test results are presented to validate the analysis.