Grid-Connected Power Converters with Distributed Virtual Power System Inertia

Renewable energy generators, e.g. wind turbines and photovoltaic (PV) arrays, have been increasingly employed to replace conventional gas/steam turbines so as to reduce greenhouse gas emission. However, such generators are normally coupled to the power grid through fast-response power converters without any inertia, leading to decreased power system inertia. As a consequence, system frequency deviations may easily go beyond the acceptable range under frequency events or contingencies, resulting in undesirable load-shedding or even blackouts. In order to address the inertia issue, this paper proposes a concept for all the grid connected power converters to realize distributed virtual inertia. This can be achieved through regulating the dc-link voltages of power converters so that their dc-link capacitors are aggregated into an extremely large capacitor for frequency support. Moreover, the decisive factors of virtual inertia are identified and analyzed. Simulation and experiment results indicate that more than 10% frequency deviation reduction and 50% improvement of rate of change of frequency (ROCOF) can be expected with the proposed concept.