Modeling And Control Of A Fast Steering Mirror System For Wireless Laser Communication In Marine Environment

Wireless laser communication technology applied in the marine environment has broad prospects with its unique advantages.However,the laser beam propagate on the sea is vulnerable to the influence of atmospheric turbulence,which causes position offsets and angle fluctuation on the receiver.The turbulence seriously reduces the efficiency of laser communication.The fast steering mirror?FSM?system is used to correct the beam offsets in real time,so that the laser beam can be stably matched with the receiver.Due to the limits of actuator's hysteresis,dynamic and the coupling characteristics between actuators,the traditional controller is difficult to control FSM fast and accurately.The effect of correcting and closed-loop bandwidth of system are greatly reduced.In our work,An FSM system platform is built.The hysteresis of FSM is compensated by using feedforward control method.According to the FSM structure and hardware space distribution,the physical model of the system is derived for numerical modeling's reference.Subspace identification is used to establish the dynamic coupling model of the open-loop FSM system based on the experimental data.The accuracy of the model and the feasibility of the modeling method are evaluated by test.The H₂ optimal controller is designed based on the dynamic coupling model to improve the performance of the closed-loop system.Comparison between dynamic coupling model and static model is provided.The experimental results show that the maximum hysteresis of FSM is reduced from 11.29%to 1.4%after compensation.The VAF?Variance accounted for?value of the dynamic coupling model of FSM system reaches 97%,which is a great improvement compared with the traditional static model,while the VAF value of static model reaches 65%.The H₂ controller makes the closed-loop bandwidth of the system reach 219 Hz,which is also a significant improvement compared with the traditional static controller,while the bandwidth of the system using static controller reach 100 Hz.The idea of applying subspace identification and H₂ controller to FSM system is proposed in our work.The feasibility of hysteresis compensation,system modeling and controller design method is proposed and verified in this thesis,the results can be used in the FSM system used in wireless laser communication in marine environment to improve the system performance,correct the beam offset,further improve the efficiency of communication.