Acceleration harmonic cancellation of electro-hydraulic servo shaking table

Nonlinearities are inherent in electro-hydraulic servo shaking table. Some nonlinearities are dead zone of servo valve, backlash and friction between joints, and friction in hydraulic cylinder. Nonlinearities cause harmonic distortion of the output acceleration signal corresponding to a sinusoidal input. On the basis of extensive studies on literature related to dead zone, backlash and friction compensation scheme, an adaptive harmonic suppression strategy based on adaptive notch filter technology is proposed. The task is accomplished by generating reference signals with frequency to be suppressed from the output. According to the error between the input acceleration and the feedback acceleration, the weights of filter are adjusted on-line by least mean square adaptive filtering algorithm in real-time. The reference inputs are weighted by the adaptive filter in such a way that it closely matches the harmonic. The output of the adaptive filter is a harmonic replica and is injected to the fundamental signal such that the output harmonic is suppressed, and the total harmonic distortion is greatly reduced. The above course is used as a basis for the development of adaptive harmonic cancellation algorithm.