Research On Acceleration Harmonic Cancellation Of Electro-Hydraulic Servo Shaking Table

Shaking table system is a very important experimental apparatus in engineering research. It is widely applied to many main industrial fields including aerospace, automobile, architecture, etc. When performed a vibration test, specimen is mounted to the test table and simulative load force is applied to the specimen. Researchers analyze the influence on load brings, the reliability of the specimen, or the damping system's performance. With the reliability requirement of industrial products, especially for aerospace vehicles, becoming higher and higher, the simulative vibration test system, as the vital apparatus of reliability test, is placed more emphases on its performance. For electro-hydraulic simulative vibration test system, how to get over the uncertainty of the system, meeting the special requirement of the shaking test, becomes a main subject.The thesis firstly gives an overview of related researches both at home and abroad, as well as a statement of thesis objectives, and of the general structure and research contribution of this thesis. The work principle of the electro-hydraulic servo shaking table, and its hardware and software configuration, are described. Three variables controller is developed based on pole placement theory to improve system stability and extend its bandwidth. Sinusoidal tests are also done.Due to the nonlinearity characteristics present in the electro-hydraulic servo shaking table, phase delay, amplitude attenuation and spurious harmonics appear in the system acceleration response when corresponding to a simple sinusoidal signal, which causes harmonic distortion of the acceleration signal. Experiment demonstrates that the harmonics'frequencies are always integer multiples of the fundamental frequency.To eliminate the phase delay and amplitude attenuation of acceleration response, amplitude-phase control (APC) network is developed. The task is accomplished by adjusting the weights using LMS algorithm when there exits phase delay and amplitude attenuation between the input and its corresponding acceleration response. The reference input is weighted in such a way that it makes the system output track the input efficiently. The weighted input signal is added to the control system such that the output phase delay and amplitude attenuation are all cancelled. The above concept is used as a basis for the development of APC algorithm.The method for harmonic cancellation based on adaptive notch filter technology is developed. The task is accomplished by generating reference signals with frequency that should be eliminated from the output. 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 cancelled leaving the desired acceleration signal alone, and the total harmonic distortion (THD) is greatly reduced. The weights of filter are adjusted on-line by using LMS adaptive filtering algorithm. The above course is used as a basis for the development of adaptive harmonic cancellation (AHC) algorithm. AHC algorithms, both based on traditional LMS algorithm and based on normalized LMS algorithm, are all developed and are compared with each other. From the comparison results, it is seen clearly that the AHC algorithm, based on normalized LMS algorithm, has better harmonic elimination efficiency and faster weight convergence.Both the APC and the AHC need not to estimate the system model. The advantages of the proposed control schemes are that it has simple structure, low computation burden and high real-time performance.