Harmonic Suppression of Ultralow-frequency Standard Vibration based on Iterative Learning Control

Calibration of ultra-low frequency (ULF) vibration is of great significance and degree of difficulty, because the maximum amplitude of acceleration produced by electromagnetic standard vibration exciters is limited by stroke and decreases with vibration frequency by 12 dB/Oct. Therefore, the signal to noise ratio decreases correspondingly and harmonic distortion of ULF standard vibration becomes a challenging problem to be solved. A harmonic suppression method based on iterative learning is proposed in this paper. The system characteristics of ULF standard vibration exciters are studied, a PD-type iterative learning control method based on displacement feedback is introduced to eliminate disturbances by PD control and suppress repetitive disturbance moments by iterative learning, thus to effectively improve the signal-to-noise ratio and accuracy of ULF standard vibration waveforms. Simulation results show that this method can effectively reduce the tracking error of the system, and harmonic distortion of acceleration waveform is reduced from 1% to 0.03% after four times of iteration.