Abstract
The recent power cut incident in the UK on 9th August 2019 indicated that frequency control to raise frequency nadir and eliminate frequency second dip is highly desirable for power grids with high penetration of wind energy. This paper proposes a fast frequency support scheme for wind turbine systems (WTSs) that can enable frequency nadir to be significantly raised and close to the settling frequency and eliminate frequency second dip. In the proposed frequency support scheme, in order to achieve similar frequency support performance and ensure stability of WTSs under varying wind speeds, different levels of wind power penetration and system conditions, an adaptive gain, which is a function of real-time rotor speed and wind power penetration level, is proposed. In the proposed scheme, rotor speeds of WTSs are proposed not to be recovered to the optimal operating points during the primary frequency control, but recovered during the secondary frequency control. Simulation results on the IEEE two-area power system with a doubly fed induction generator (DFIG)-based wind farm and the IEEE 39-bus power system with permanent magnetic synchronous generator (PMSG)-based wind farms using real-time digital simulator (RTDS) and Dymola are presented to verify the effectiveness of the proposed scheme.
Highlights
W ITH the increasing level of wind power penetration, frequency stability of power system has drawn considerable attentions from system operators [1], [2], as currently the dominant variable speed wind turbine systems (WTSs) are mostly operating at maximum power point tracking (MPPT) mode and do not regulate their active power to support the power grid when the grid frequency deviates from its nominal value
This paper has proposed a fast frequency support scheme for WTSs by making use of the stored kinetic energy to significantly raise frequency nadir (FN) to be close to the settling frequency without frequency second dip (FSD)
In other words FN is arrested and raised to a high level close to the settling frequency; (b) Ensuring consistent superb FN improvements under different operating conditions: the proposed adaptive gain is a function of the real-time rotor speed and wind power penetration level
Summary
Rotor speed of a DFIG or PMSG ωr opt ωr max ωr min ωr lim fsys fnom f df /dt Kp(ωr , pl) g(pl) k(ωr ). Optimal rotor speed under MPPT control Rated rotor speed Cut-in rotor speed Rotor speed threshold below which the proposed frequency support scheme is not allowed Grid frequency Nominal grid frequency Frequency deviation Frequency derivative Dynamic gain of f in the proposed fast frequency support scheme Dynamic gain in Kp (ωr , pl) = g(pl)k(ωr ) to adapt to different wind power penetration levels Dynamic gain in Kp (ωr , pl) = g(pl)k(ωr ) to adapt to different wind speeds.
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