An Overview of Inertia Emulation Strategies for DC Microgrids: Stability Analysis and AC Microgrid Analogies
Authors: Mahdis Haddadi, Saman A. Gorji, Samson S. Yu
Abstract:
In response to environmental concerns and the need to conserve fossil fuel resources, the integration of Distributed Generators (DGs) has increased significantly in modern power systems. DGs, which include Renewable Energy Sources (RESs), Energy Storage Systems (ESSs), and new load types such as Electric Vehicles (EVs), represent a shift toward cleaner, more sustainable energy practices. Microgrids have emerged as a key solution for integrating DGs, RESs, and ESSs into the grid. They are classified as either Alternating Current Micro-Grids (AC-MGs), Direct Current Micro-Grids (DC-MGs), or hybrid microgrids, depending on the voltage type at the point of common coupling.
However, with the rapid expansion of RESs, both AC and DC MGs are increasingly characterised as weak power systems. The high penetration of inertia-less Photo-Voltaic (PV) and wind energy sources significantly impacts system stability, as the Static Power Electronic Converters (PECs) connecting RESs to the grid lack the mechanical inertial response provided by traditional rotating machines. In conventional power systems, the grid frequency is directly linked to the rotational speed of all connected machines, with the overall inertia determined by the total rotating mass. This inertia reflects the system’s resistance to frequency variations tied to the angular-speed stability of connected rotating masses.
Unlike traditional generators, RESs connected through PECs are decoupled from grid frequency. This results in a reduced capacity to provide inertia. Meanwhile, PECs’ fast response can lead to low inertia and weak damping, creating significant challenges for frequency stability in AC systems. In contrast, DC systems are more impacted by voltage stability concerns. To address these challenges, leveraging the controllability of PECs is an effective approach. This highlights the practical importance of virtual inertia and damping control (VIDC) for regulating active power and maintaining power balance.
Providing a comprehensive overview, and highlighting recent advancements and potential future directions is essential for helping researchers gain a detailed understanding of VIDC control methods in DC-MGs, as well as the analogies between AC and DC systems. Such an investigation into the behaviours of grid-forming and grid-following converters offers valuable insights into their operational principles and implications for control strategies.
Additional Information:
We are applying these principles in real-world deployments at Deakin University’s Renewable Energy Microgrid, focusing on battery installation, system integration, and a smart deployment strategy developed through the Recycling and Clean Energy Commercialisation Hub (REACH) within the Centre for Smart Power and Energy Research (CSPER). The program translates VIDC-based control and stability insights into campus-scale operations and industry-facing prototypes.