Frequency-Response Methods for Synthesizing Controlled High-Speed Electric Drives of Compressors

Abstract

Frequency-response methods for analyzing and synthesizing current and electromagnetic torque control loops in alternating-current electric drives are proposed. It is shown that, when solving the problems of analysis and synthesis of the current and torque control loops, the unchanged part of the electric drive can be approximated by a linear system with the amplitude-modulated signal. It has been established that the transient and steady-state processes of variables in the motor’s phase windings can be considered in the current and torque loops independently. The use of frequency-response methods for identification of controlled objects allows consideration of the cross-magnetic links between the three-phase windings of the electric machine and the mathematical description of the system can be represented by a simplified set of equations, which is convenient for setting up and adjusting the system by engineering personnel. Using experimental Bode plots, it has been shown that the steady frequency passband in the current control loop can reach 4000 rad/s, which facilitates the adjustment of the toque control loop when the drive is running at a speed of 6000 rpm. A further increase in the speed of the drive with the specific mass and dimensional parameters preserved at the same level can be achieved only by introducing correction signals. It is shown that in multiphase electric drives with more than three phases, the phase winding zone decreases and the leakage inductive reactance of the phase winding decreases, which allows a significant expansion of the frequency passband in the current, torque, and speed control circuits.