The Impact On Frequency Stability With Participation Of Wind Turbines Based On Direct-Drive Permanent Magnet Synchronous Generators

Power system frequency stability may deteriorate with the increasing penetration of the wind power. The maximum power point tracking (MPPT) operation of wind power is no longer the most economic strategy. Thus wind power participating in frequency regulation (FR) makes sense and by which the impact on frequency regulation should be researched further.This paper focuses on the direct-drive permanent magnet synchronous generator (DDPMSG) and analyses the impact on frequency stability by PMSG participating in primary frequency and virtual inertial control. The main studies are presented below.(1) Variable speed wind turbine generators (VSWTGs) may operate with active power reserve by overspeed and pitch angle control. Based on active output increment of the wind turbines, difference between steady-state frequency deviations without and with wind power frequency regulation is defined to quantify contribution of the WTGs to decrease frequency deviation. The critical load increment fully utilizing the active power reserve of the wind turbines is determined. Besides, the average system frequency model including primary FR strategies of the WTGs and the thermal generators is proposed, whose linear form is derived for eigenvalue analysis. The parameters for the pitch angle control are chosen based on the locus of the eigenvalues.(2) The VSWTG may participate in frequency regulation by virtual inertial control to release the kinetic energy. Its motion equation is linearized, which together with frequency regulation characteristic of the synchronous generators yields the transfer functions of grid frequency and VSWTG’s rotor speed versus load change, which extends the existing low-order average system frequency (ASF) model.(3) The VSWTG needs frequency control signal to participate in frequency regulation. The two different signals including the center of inertia (COI) frequency and the point of common coupling (PCC) frequency are used to form the eigen matrix of the multi-machine system with PMSG. Numerical analysis is applied to compare the differences.(4) Accurate time domain dynamic simulation ensures the deep research of PMSG participating in frequency regulation. Disturbance such as sudden change of active load may cause phase angle jump, in which normal trapezoidal integration method may result in unreasonable frequency simulation results like numerical oscillation. The simulation results under trapezoidal integration with damping method and Gear second order methods are compared.