The satellite laser communication pointing system driven by a permanent magnet synchronous motor (PMSM) should have high-precision fixed-point pointing and tracking performance. However, the system motor parameter perturbation and friction disturbances affect the performance of the system. A composite control strategy for the space laser pointing mechanism based on an active disturbance rejection controller (ADRC) is proposed to solve these problems. In order to mitigate the adverse effects of current loop parameter perturbation and speed loop friction disturbance on control performance, the improved current controller and speed controller based on ADRC are designed. On these bases, an improved feedforward position controller is designed. The proposed control strategy can effectively suppress the parameter perturbation of the current loop and the friction disturbance of the speed loop, thus improving the position tracking accuracy of the pointing mechanism for the laser communication system. Experiments are carried out based on the laser pointing mechanism platform to demonstrate the correctness and effectiveness of the proposed strategy.INDEX TERMS Laser pointing system, active disturbance rejection controller (ADRC), parameter perturbation, friction disturbance, feedforward position controller
I. INTRODUCTIONCompared with radio frequency communications, laser communication has a higher transmission rate, larger communication capacity, advantages of small size, lightweight, and high confidentiality [1], which has attracted widespread attention. As a critical part of space laser communication, the pointing mechanism for the laser communication system is responsible for the acquisition, tracking, and targeting (ATP), which determines whether a reliable communication link can be established [2]. The composition block diagram is shown in Figure 1, and the main equipment is a high-precision servo based on PMSM.The driving object of the ATP system is a narrow laser beam, and its beam divergence angle is usually about 50 μrad. Therefore, the laser pointing system requires higher fixed-point pointing and stable tracking accuracy. However, temperature changes and magnetic field interference exist in the space working conditions. As the