Research On Disturbance Observer Based Control Methods In Photoelectric Tracking System

The photoelectric tracking system is affected by the changes in environments and loads,ground vibration,friction,and other factors,which lead to the reduction of imaging stability and tracking accuracy.In recent years,the photoelectric tracking system has been mounted on moving platforms,such as vehicles,airplanes,and satellites.In complex working environments,the moving platforms bring non-negligible external disturbances and internal modeling uncertainties to the photoelectric tracking system.It means that there are severe challenges to achieving the higher accuracy of optical stabilization in the inertial space.Therefore,it is very important to improve the disturbance suppression capabilities of the inertially stabilized platform in the photoelectric tracking system on the moving platform to reject the external disturbances and modeling uncertainties.Aiming at the problem that the existing disturbance-observer-based control(DOBC)methods in the photoelectric tracking system are limited to the low-bandwidth position loop,and the problem of changing the tracking characteristics,losing the stability margins or the disturbance rejection capabilities to ensure the stability of the nonminimumphase(NMP)system in the high-bandwidth inertial loop,several modified DOBC methods are proposed in this paper.The research work is as follows:Firstly,this paper analyzes the feedforward control method based on disturbance measurement and compares it with the existing DOBC method based on disturbance estimation.By taking advantage of the high-frequency characteristics of the inertial accelerometer and low-frequency characteristics of the charged-couple device,the virtual gyroscope is obtained to replace the fiber-optical gyroscope with the frequency-domain fusion method.The virtual multi-loop feedback system is established with the virtual gyroscope.The replaced fiber-optical gyroscope is installed on the carrier platform to directly measure external disturbances.The measured disturbances are fed forward to the control loop through an ideal compensator.This paper theoretically analyzes the frequency-domain fusion method with multiple sensors,which derives the ideal compensator design method and stability constraints.The experiments prove that the proposed method can reduce the load and effectively reject the external disturbances of the photoelectric tracking system,without increasing the hardware cost or breaking the system’s stability.Secondly,the paper discusses the compensation control method to suppress both external and internal disturbances based on disturbance estimation.In the high-bandwidth inertial loop of the optoelectronic tracking system,existing DOBC methods have the problem of changing the tracking characteristics,losing the stability margins,or disturbance suppression capabilities to ensure the stability of the NMP system.Therefore,a novel disturbance observer method is proposed to reject the low-frequency disturbances.The NMP system’s stability constraints,filter design method,disturbance suppression performances,and robustness are analyzed theoretically.The experimental results prove that the proposed method does not change the tracking characteristics or stability margins,and effectively improves the low-frequency disturbance suppression capability of the NMP optoelectronic tracking system,which has a better suppression effect on a mass of low-frequency disturbances caused by the carrier platform.Thirdly,a partially compensated disturbance-observer-based control(PC-DOBC)method with dual filters is proposed to further improve the disturbance suppression capabilities of the NMP photoelectric tracking system in low-and-mid frequency bands.This paper analyzes the different stability constraints of dual filters and discusses the estimation performances for external and internal disturbances.Benefiting from the linear superposition of dual filters,the PC-DOBC method realizes partial compensation of disturbance estimation between the filters.The PC-DOBC method with dual filters has better disturbance estimation and suppression performances than the DOBC methods with a single filter.Experiments prove that the PC-DOBC method can effectively improve the disturbance suppression capabilities in the low-and-mid frequency range,without changing the tracking characteristics or stability margins of the NMP photoelectric tracking system.Finally,aiming at the problem that the PC-DOBC method still loses the disturbance estimation performances to stabilize the NMP systems,a fully compensated disturbanceobserver-based control(FC-DOBC)with dual filters is proposed,which further solves the disturbance rejection problem of the NMP optoelectronic tracking systems.In this paper,the stability constraints of the single-filter and double-filter FC-DOBC methods are analyzed respectively.Although the primary filter has to lose disturbance estimation performances to stabilize the NMP system,the compensatory filter can make up for the loss of the primary filter.Thus,the filters can complement each other in disturbance estimation.Experiments show that the FC-DOBC method does not change the tracking characteristics or stability margins,and can fully suppress the external disturbance and internal disturbance within the high-bandwidth inertial loop range of the NMP photoelectric tracking system.