Harmonic cancellation for electro-hydraulic servo shaking table based on LMS adaptive algorithm

An electro-hydraulic shaking table which is based on acceleration control is studied here. A three-variable control scheme is applied to achieve robustness, disturbance suppression and sufficient frequency bandwidth. Its acceleration response contains harmonics corresponding to sinusoidal input because of nonlinearities in the system. To reduce harmonic distortion and improve control performance of the shaking table, a harmonic cancellation algorithm is developed. The weights of the proposed algorithm are on-line updated by the normalized LMS algorithm. The reference input with input frequency is filtered by the adaptive LMS filter. The output of the adaptive filter is a close harmonic replica and is added to the fundamental signal such that the output harmonic is cancelled leaving the desired signal alone, and the total harmonic distortion is greatly reduced. Experimental results demonstrate the efficiency and validity of the proposed control scheme.