SPRUHJ1I January 2013 – October 2021 TMS320F2802-Q1 , TMS320F28026-Q1 , TMS320F28026F , TMS320F28027-Q1 , TMS320F28027F , TMS320F28027F-Q1 , TMS320F28052-Q1 , TMS320F28052F , TMS320F28052F-Q1 , TMS320F28052M , TMS320F28052M-Q1 , TMS320F28054-Q1 , TMS320F28054F , TMS320F28054F-Q1 , TMS320F28054M , TMS320F28054M-Q1 , TMS320F2806-Q1 , TMS320F28062-Q1 , TMS320F28062F , TMS320F28062F-Q1 , TMS320F28068F , TMS320F28068M , TMS320F28069-Q1 , TMS320F28069F , TMS320F28069F-Q1 , TMS320F28069M , TMS320F28069M-Q1
Disturbance rejection tests a controller's resistance to external disturbances, which will impact the motor speed and position. Disturbance rejection is measured using the maximum error and settling time. The maximum error shows the deviation from the goal position, and is an indication of how aggressively your controller is tuned. Aggressive tuning will produce a low maximum error.
Settling time refers to the amount of time from the point when the disturbance happens until the position returns to a fixed band around the goal position. This is also an indication of how aggressively your control loop is tuned. If the controller is tuned too aggressively it will have a long settling time because it will oscillate around the goal position before settling.
Figure 13-16 and Figure 13-17 show the difference between poor tuning and optimal tuning of the same controller. As you can see by tuning the position controller, when torque is applied or removed from a motor system the tuned controller greatly reduces the maximum error and settling time. This is an exaggerated example, but it is used to highlight the importance of getting a good tuning for your system.
When doing disturbance rejection testing it is important to test at multiple speed and load combinations. Position controllers have different performance characteristics when placed into different situations. In order to properly evaluate the effectiveness of your position controller, tests should be done across the entire application range. The test results will indicate whether the controller will meet the application specifications, or whether the controller needs to be tuned multiple times for different operating points.
It is also important to be able to create repeatable disturbances. This can be accomplished using a dynamometer or a disturbance motor. Creating repeatable disturbance is an important factor when evaluating multiple controllers. If test conditions cannot be replicated, it is difficult to adequately compare the responses of two controllers.