Research On Speed Control Method Of Solar Array Servo System

With the rapid development of small satellites,long-term and high power consumption payloads,such as communication,navigation,etc.,are more and more deployed on small satellites.So,it is necessary for small satellite to equip with solar array servo system.This servo system can make the solar array always point to the sun,and the payload point to the mission direction.The main difficulties of the servo system lie in: 1)the change of system model parameters because of the complex and changeable environment;2)the demand of high-quality speed feedback signal;3)the complex dynamic behavior of the nonlinear system composed of permanent magnet synchronous motor(PMSM)and flexible load of solar array.To overcome the above difficulties and realize the high precision and robust speed tracking control of the solar array servo system,the main research contents of this paper are as follows.Firstly,the controller needs to obtain the real-time and accurate speed feedback signal.However,the position quantization error of the limited resolution encoder is large when the solar array runs at ultra-low speed,and the speed feedback signal calculated from position difference contains severe noise,resulting in actual speed oscillation.In this paper,the speed observation process in feedback channel is mathematically modelled and the speed oscillation induced by the observation noise is fully analyzed.Based on the built model,a novel speed estimator using improved tracking differentiator is proposed and the related parameters are suitably tuned.Meanwhile the high-quality differential signal obtained by the improved tracking differentiator will be used in the data-based identification of the servo system.Then,the dynamic characteristics of the servo system are fully analyzed.The model of PMSM is affine transformed into a typical Lorentz equation,and the chaos of PMSM is judged by three tools: Bifurcation Diagram,Lyapunov Exponent and Poincaré Section.Then,considering the flexible load of the solar array,the main parameters of the system,including the friction damping coefficient of the rotor,the friction damping coefficient of the internal structure of the hinge and the equivalent spring stiffness coefficient,are analyzed in this paper.Under the influence of these parameters,the servo system will sink into chaos,which will cause the non-periodic oscillation of torque and speed.After obtaining the knowledge of solar array servo system,chaos control is applied in this paper.Firstly,the model of servo system,including the PMSM model and the solar array model,is identified from the current and speed data by employing the sparse identification.Because the differential signal of data is needed in the identification algorithm,the improved tracking differentiator mentioned above is used here.Finally,the servo system is controlled by state feedback,and the best state feedback gain is calculated from the identified system parameters,so that the poles of the closed-loop system can be assigned to the desired position,and the dynamic response characteristics can meet the desired target.Simulation shows that the control results meet the expectations,and the solar array servo system can run stably when the environment changes.