Distributed Power System Virtual Inertia Implemented by Grid-Connected Power Converters

TLDR

Renewable energy sources such as wind and solar are increasingly deployed, but their power converters lack inertia, causing grid frequency to drift beyond limits during severe events. This work introduces distributed virtual inertia that can be realized by grid‑connected power converters to mitigate the inertia deficit. The approach emulates system inertia by using the dc‑link capacitor energy, regulating its voltage proportionally to grid frequency to form a large equivalent capacitor, and characterizes its limits and design parameters. Simulations and experiments confirm the concept, achieving 12.5 % improvement in frequency nadir and 50 % in rate‑of‑change‑of‑frequency.

Abstract

Renewable energy sources (RESs), e.g. wind and solar photovoltaics, have been increasingly used to meet worldwide growing energy demands and reduce greenhouse gas emissions. However, RESs are normally coupled to the power grid through fast-response power converters without any inertia, leading to decreased power system inertia. As a result, the grid frequency may easily go beyond the acceptable range under severe frequency events, resulting in undesirable load-shedding, cascading failures, or even large-scale blackouts. To address the ever-decreasing inertia issue, this paper proposes the concept of distributed power system virtual inertia, which can be implemented by grid-connected power converters. Without modifications of system hardware, power system inertia can be emulated by the energy stored in the dc-link capacitors of grid-connected power converters. By regulating the dc-link voltages in proportional to the grid frequency, the dc-link capacitors are aggregated into an extremely large equivalent capacitor serving as an energy buffer for frequency support. Furthermore, the limitation of virtual inertia, together with its design parameters, are identified. Finally, the feasibility of the proposed concept is validated through simulation and experimental results, which indicate that 12.5% and 50% improvements of the frequency nadir and rate-of-change-of-frequency (RoCoF) can be achieved.