Experiments In H_? Control For Frequency Fluctuating Disturbances In The Floating Raft Active Vibration Isolation System

Reducing the vibrations produced by power machines can effectively improve the concealment and reconnaissance capability of naval vessels.Vibration isolation technology is one of the effective means to reduce mechanical vibration.Since active control methods can overcome the defect of passive methods that the passive methods cannot effectively suppress the vibration in low frequency domain,they are investigated extensively.The disturbances are mostly regarded as periodic signals in the existing active vibration control methods.However,the vibration produced by power machines is frequency fluctuating disturbances.It needs further study that whether the existing control methods have good vibration suppression ability for such disturbances.Feedback control method can effectively suppress frequency fluctuating disturbances.The mathematical model of controlled object is necessary when use this method to design controller.The difference between the model and the real object will influence the stability of the designed closed-loop control system.H_?control method can effectively solve the model's uncertainty.The controller designed by this method has strong robust stability.What's more,H_?control method can reshape the frequency response function of the closed-loop system.The designed system can effectively suppress the frequency fluctuating disturbances.In this dissertation,H_?control method is adopted to suppress frequency fluctuating disturbances produced by power machines.Simulations and experiments are conducted to validate the validity of this method.The main content of this dissertation includes three chapters.They are the modeling of the control channel of the floating raft active vibration isolation system,the design of H_?controllers for suppressing the frequency fluctuating disturbances,and the H_?control experiments in the floating raft active vibration isolation system.The system identification experiments were designed and executed.Two inputs two outputs continuous transfer function models were identified by using the system identification toolbox.Besides,the model was validated both in time and frequency domain,whose value of best fit in time and frequency domain all are above 85%.The controllers were designed by the plastic design method based on the mixed sensitivity problem.The selecting method of weighted functions was studied.Two controllers were designed for SISO system.One of them can suppress single frequency fluctuating disturbance and another controller can suppress double frequency fluctuating disturbance.For MIMO systems,a controller was designed to suppress single frequency fluctuating disturbances.The stability and performance of controllers all above are analyzed.The simulation results indicated that the error signals'amplitude was reduced by more than 50%and the main frequency amplitude of the error signals was reduced by more than 10dB after the control.In order to verify the effectiveness of these controllers,single excitation single channel control experiments,multiple excitations single channel control experiments and single excitation multiple channels control experiments were executed in the floating raft active vibration isolation system.Experiments achieved obvious effect to reduce vibration.The RMS(Root Mean Square)value was decreased by more than74%and the amplitude of the main frequency in the error signal reduced by more than 13dB.The results of simulations and experiments are basically identical.