This example demonstrates using TDFS* to identify the open-loop transfer function of a closed-loop motion control system. Typical "AC" or frequency-domain analysis cannot be performed on this system for several reasons, including the sampled-data nature of the D-Q control algorithm, the switching of the space-vector modulated (SVM) drive inverter, and the non-linear stick-slip friction characteristic.
The open-loop gain (dBMag, blue) and phase (red) are shown in the on-schematic waveform viewer. Note that the unity gain crossover frequency is just below 5 Hz, and the phase margin is just under 34 degrees. This can be compared with the overshoot/ringing of the step response, observed in the time-domain simulation of the companion example: "Motion Control System with PMSM and SVM Drive - Step Response".
*To learn more about the Time Domain Frequency Response (TDFS) method, see our Blog Series: TDFS Part 1, 2 and 3.