Disturbances Rejection Controller Design For Mobile Carrier Antenna Servo Systems

With the promotion of communication demands,satellite communication antenna developed toward miniaturization,mobilization and high reliability and it also began to play an increasingly important role in military,industry and civilian fields.Different from fixed antennas,difficulties of the moving carrier based satellite communication antenna lay in suppressing disturbances caused by carrier movement to antenna pointing accuracy.At present,it was required by mainstream Ka-band radar beam width that the pointing error should be less than 0.4° however,disturbances of the carrier could be up to dozens of times of this value;especially in terms of the land carrier,bumps in the road and changes in movement status of the carrier itself were able to generate disturbance with large amplitude and wide frequency band.As a result,higher requirements were presented for disturbance rejection capability of the antenna servo system.Previously,the “Communications On The Move” system adopted a control strategy based on classical PID in most cases.Due to such simple control structure and the convenience for engineering realization,it played a good part in airborne and ship borne antenna servo systems.Nevertheless,considering the special performance of disturbances suffered by the land carrier,it was less likely for the PID controller to achieve a favorable effect on the premise of resonant antennas.In comparison,the controller designed in accordance with modern control theories may become a breakthrough for further improvement of the corresponding disturbance rejection performance.On account of practical engineering application needs,a 0.8 meter “Communication On The Move” antenna servo system provided by the CETC54 was studied from a perspective of disturbance rejection control in this paper.Firstly,hardware constitution and characteristics of this system were analyzed and a simulation experiment platform constructed could be used as a reference for controller design.Dependent on characteristics of all hardware,a model form of the antenna servo system was presented here by taking rigidity,flexible modality and time delay of it into a comprehensive account;moreover,Hankel identification method based on impulse responses was also employed with an aim to determine various model parameters of the object.Subsequently,in view of tracking performance,a state feedback controller and a state observer were both designed according to linear quadratic index;and,the optimal H₂ characteristic was also proved for the output feedback controller obtained.However,considering that road disturbance was provided with a certain model,the performance of H₂ optimal controller was not that required by engineering applications.Thus,after data of disturbance have been collected through experiments,the method of subspace identification was then taken to determine a disturbance statistical model.According to it,a disturbance observer and a disturbance filter were added into the original H₂ controller to strengthen the capability of feedback controller to suppress low frequency disturbances.As the disturbance model still had great energies in some middle-high-frequency bands,a feed forward controller was also designed here on the basis of H_∞ optimal method;in addition,the rejection band was also adjusted by virtue of weighting functions so as to achieve the expected results.In the end,a discrete approach was provided for all controllers described above,which was convenient for engineering realization.Furthermore,rationality of this design was also verified by masses of experiments.Among them,the controllable disturbance experiment has proven the model and the simulation platform established here to be truly effective;the swaying bench experiment demonstrated advancement and validity of the feedback controller design method used in this paper;the dynamic car experiment sufficiently proved both superiority and reliability of the designed feed forward and feedback controllers by inspections in actual usage scenarios and it was also able to resolve the associated engineering application difficulties in real sense.Besides,feedback and feed forward control strategies of high application values described in this paper could be independent of hardware platforms to be applied into various occasions requiring disturbance rejection.