MTS Series 793 - Manual (Page 252)

About Adaptive Harmonic Cancellation (AHC) Compensators
Adaptive Harmonic Cancellation (AHC) works with Amplitude Phase Control (APC) to minimize spurious
harmonic distortion.
Adaptive Harmonic Cancellation allows you to set up adaptive harmonic cancellers to reduce or cancel
spurious harmonics in the feedback when programming sine waves. This approach injects input harmonics
into the controller command waveform with just the right phase and amplitude to cancel the feedback harmonics.
Adaptive Harmonic Cancellation is:
• Typically used when programming with pure sinewave commands or sine sweeps in acceleration control.
• Typically used in high-frequency MAST systems for ground vehicle testing.
Note:
The adaptive harmonic cancellation function is available only when Amplitude Phase Control (APC)
is on.
AHC theory
Because cancellation occurs at the system output by means of a signal at the system input, the phase response
of the system must be known.
• The Estimated Feedback (Fdbk) Model, or “model” for short, is an adaptive finite-impulse-response (FIR)
filter, and provides the phase response.
• Before you turn cancellation on, you must train the system phase response by commanding the system
with a sine sweep or a random signal over the frequency range of operation.
• Once the AHC model is trained for a test, you can save the AHC model settings to a reference set that
can be saved as part of a parameter set. When you run subsequent tests, you can copy these settings
into the current model and run the test. When running subsequent tests, the effect of the AHC compensator
will not immediately be apparent because the system must restart the tracking process to optimize system
coefficents.
AHC Tab Settings
Description Item
Displays the frequency of the control system model FIR filter. Model Filter Count
Sets and displays the rate at which the Least-Mean-Square algorithm
converges to the optimum coefficients in the model. Train Convergence Rate
Sets and displays the rate at which the Least-Mean-Square algorithm
converges to the optimum coefficients in the system. Typically this
should be set to 1 or less. Track Convergence Rate
252 MTS Series 793 Control Software
Station Setup