Micro-Disturbance Compensation Method for Ultralow Frequency Vibration Waveform of Electromagnetic Vibrator

To produce a standard ultralow frequency (ULF) vibration waveform for calibration with an electromagnetic vibrator (EMV) is challenging because of its tiny electromagnetic driving force and low signal-to-noise ratio (SNR). This article presents a model-free compensation method for the micro disturbance of the EMV, which mainly originates from nonlinear forces generated by the bending or tensioning of pipes and wires. The influence of micro disturbance on the system is analyzed to extract the disturbance current without estimating the equivalent model and compensated in the input; thus, the force sensorless and model-free compensation of micro disturbance is realized in real-time. Experimental results in the frequency range of 0.001-1 Hz indicate that the proposed method reduces the displacement tracking error by 10.14% and the total harmonic distortion (THD) by 19.44% relative to the model-based compensation method. The proposed method effectively reduces the THD of the ULF vibration waveform with a low computational burden. It can be widely used for ULF vibration generation in engineering applications.