A frequency control scheme of a doubly-fed induction generator considering random wind speeds

Abstract

The low inertia characteristic of the power system is increasingly prominent with the increase of wind power penetration. Therefore, the threat of random wind speeds and sudden frequency events to the frequency stability of a low inertia power system is further enhanced. It is necessary for wind power generators to provide frequency auxiliary service for the power system through appropriate control schemes. To address these issues, a frequency control scheme is proposed for a doubly-fed induction generator (DFIG) to support the frequency stability of the system in this paper, which can play a role in additional-loop-based frequency smooth control (FSC) and dynamic inertial control (DIC) by a smooth switcher. The objective of FSC is to smooth the frequency fluctuation caused by random wind speeds, load fluctuation, etc., while DIC aims at improving the frequency nadir (FN) and simultaneously preventing rotor speed over-deceleration during a large disturbance. In addition, a smooth switcher is proposed to coordinate the advantages of FSC and DIC. Note that the proposed approach can be automatically switched from FSC to DIC, while frequency deviation exceeds the given threshold due to a large disturbance. Finally, simulation results on the IEEE 14-bus system show the advantages of the proposed method in improving frequency stability under real complex situations while ensuring the stable operation of wind turbine generators.