Optimized Auxiliary Frequency Control of Wind Farm Based on Piecewise Reduced-order Frequency Response Model

With the increasing wind power penetration in the power system,the auxiliary frequency control(AFC)of wind farm(WF)has been widely used.The traditional system frequency response(SFR)model is not suitable for the wind power generation system due to its poor accuracy and applicability.In this paper,a piecewise reduced-order frequency response(PROFR)model is proposed,and an optimized auxiliary frequency control(O-AFC)scheme of WF based on the P-ROFR model is proposed.Firstly,a full-order frequency response model considering the change in operating point of wind turbine is established to improve the applicability.In order to simplify the fullorder model,a P-ROFR model with second-order structure and high accuracy at each frequency response stage is proposed.Based on the proposed P-ROFR model,the relationship between the frequency response indexes and the auxiliary frequency controller coefficients is expressed explicitly.Then,an OAFC scheme with the derived explicit expression as the optimization objective is proposed in order to improve the frequency support capability on the premise of ensuring the full release of the rotor kinetic energy and the full use of the effect of time delay on frequency regulation.Finally,the effectiveness of the proposed P-ROFR model and the performance of the proposed OAFC scheme are verified by simulation studies.

Dynamical evolution of anisotropic response of type-Ⅱ Weyl semimetal TalrTe_(4) under ultrafast photoexcitation

Layered type-ⅡWeyl semimetals,such as WTe_(2)/MoTe_(2),and TalrTe_(4)have been dem on strated as a supreme photodetection material with topologically enhanced responsivity and specific sensitivity to the orbital angular momentum of light.Toward future device applications with high performance and ultrafast response,it is necessary to understand the dynamical processes of hot carriers and transient electronic properties of these materials under photoexcitation.In this work,mid-infrared ultrafast spectroscopy is performed to study the dynamical evolution of the anisotropic response of TalrTe_(4).The dynamical relaxation of photoexcited carriers exhibits three exponential decay components relating to optical/acoustic phonon cooling and subsequent heat transfer to the substrate.The ultrafast transient dynamics imply that TalrTe_(4)is an ideal material candidate for ultrafast optoelectronic applications,especially in the Iong-wavelength region.The angle-resolved measurement of transient reflection reveals that the reflectivity becomes less anisotropic in the quasi-equilibrium state,indicating a reduction in the anisotropy of dynamical conductivity in presence of photoexcited hot carriers.The results are indispensable in material engineering for polarization-sensitive optoelectronics and high field electronics.