Adaptive notch filter applied to acceleration harmonic cancellation of electro-hydraulic servo system

The acceleration output of an electro-hydraulic servo system corresponding to a sinusoidal input contains higher harmonics besides the fundamental input, because of complex nonlinearities occurring in the system. This causes harmonic distortion of the acceleration signal. The method for harmonic elimination based on adaptive notch filter is proposed here. The task is accomplished by generating a reference signal with a frequency that should be eliminated from the output. The reference input is filtered in such a way that it closely matches the harmonic. The filtered reference signal is added to the fundamental signal such that the output harmonic is cancelled leaving the desired signal alone. The weights of the adaptive filter are adjusted by the error between the input and the feedback acceleration to eliminate acceleration harmonic, creating an adaptive notch filter. The above concept is used as a basis for the development of an acceleration harmonic cancellation algorithm. Results of simulation and experiment on an electro-hydraulic servo shaking table demonstrate the efficiency and validity of the proposed control scheme.