Abstract. The problem of experimental identification of frequency response functions of precision electric drives of actuating axis of telescopes is analyzed. Several approaches to experimental estimation of frequency response functions based on Fourier transform are considered, including empirical transfer function estimation, Welch's averaged periodogram method, short-time Fourier transform. The influence of nonlinearity and harmonic distortions on the results of experimental identification of frequency response function (Coulomb friction, cable transition moment, torque ripples and cogging torque of PMSM, dead time of the PWM inverter) is studied. An experimental scheme with a torque loop and a switched controller of the angular velocity and position, which used to limit the angular velocity and position and to provide the permanent sign of angular velocity for reducing the impact of Coulomb friction is described. Approbation of the proposed approaches to the identification experiment was carried out in MATLAB environment using mathematical model of electric drive with two-mass load and experimental data on distortions and nonlinearities obtained while tuning the telescope actuation axis. 

Keywords: experimental identification, frequency characteristics, precision electric drive, Coulomb friction torque, relay controller, Fourier transform, time-frequency analysis, window function

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