Innovated Inertia Control of DFIG with Dynamic Rotor Speed Recovery

Abstract

High wind power penetration (WPP) is challenging system frequency stability. As a countermeasure, virtual inertia controls are introduced, utilizing kinetic energy (KE) stored in wind turbine generators (WTGs) for frequency regulation. Without restoration, generation efficiency of WTGs will be degraded after inertia contribution. To counter this issue, we propose an inertia control scheme of a doubly fed induction generator (DFIG), aiming at achieving dynamic inertia recovery regarding both KE and DC link energy. An asymmetrical droop control, referred to as the rate of change of frequency (RoCoF), is proposed for KE management. The upper boundary of droop gain is extended to give full play to converters and is revised, considering the system frequency state, to counter positive feedback issues induced by reversible gain regulation, which is restricted by KE to ensure stable operations as well. The inertial DC energy needed to cooperate with KE control regarding countering small fluctuations, is improved with an orderly recovery behavior. Case studies are conducted under dynamic wind conditions and the results indicate that with our proposed scheme, the ability of dynamic inertia recovery can be obtained, bringing DFIG higher generation efficiency and more adequate operation margin for sustained regulation. Essentially, the inertial frequency response and fluctuation suppression ability is well maintained.