<p>In order to meet the current and future needs of deep space communication services, a number of new Deep Space Station antennas had to be built at the existing Deep Space Network sites. The accuracy of the antenna has to be higher to explore deeper and farther space. The influence of wind disturbance on the level of pointing error has become a serious problem with the increased size of antenna. The control system is one of the decisive factors for pointing precision, the other two factors are the quality of antenna drives and the physical structure of the antenna. Proportional integral derivative (PID) controllers have been used for several decades for antenna control system applications, primarily due to their simplicity of concept and explicit tuning procedures. But with the increasing dimensions of antennas, they are unable to suppress antenna vibrations and meet the stringent pointing requirements. A fractional-order proportional-integral-derivative (FOPID) is an extension of the classical PID controller, it has two additional parameters named the order of fractional integration and fractional derivative. The fractional-order controller is less sensitive to changes of parameters of a controlled system and controller, and it can attain the property of iso-damping very easily. For higher-order systems like antenna control systems, the performance of classical PID controllers deteriorates, whereas FOPID provides better results. In addition, fractional-order controllers can properly compensate disturbances due to undesired nonlinearities such as dead zone, backlash, hysteresis, and static distortion in the control system of the large deep space observatory antenna which results in increasing the precision of the systems. With reference to the typical antenna, this paper aims to design a fractional order controller to improve the accuracy of antenna pointing mechanisms. First, the global stability region of FOPID for the antenna plant was obtained using the D-decomposition method, which can ensure the closed-loop system is bounded-input bounded-output (BIBO) stable. Second, the parameters in the stability region were chosen using a Genetic Algorithm to achieve the minimum value of the objective function, the elaborate objective function can consider both transient performance and steady-state performance. Finally, a series of simulations and analyses about this fractional-order control system was conducted, the wind-gust load is considered as a time-varying torque plus the drive torque, the total wind velocity is the combination of a steady-state and a turbulence velocity. The results show that the fractional-order controller works significantly outperform the traditional PID controller, it achieved a remarkable amelioration in the reduction of overshoot and the capacity of wind disturbance rejection.</p>

Design of a Fractional-Order Controller for the Large Deep Space Observatory Antenna in Wind Disturbance

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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