基于时变时滞T-S模糊模型的卫星光通信精跟踪系统模糊PID控制研究

Compared with traditional microwave communication, satellite laser communication has many advantages, such as super-fast data transmission, high information confidentiality, lower power consumption, etc. When the laser communication link is established, the vibration of the satellite becomes the key factor that affects the quality of communication. Therefore，the strong disturbance suppression capability of the fine tracking system of the satellite communication terminal is required. The fine tracking system consists of a fast steering mirror driven by a piezoelectric ceramic and a CCD detector, which is a typical nonlinear system with time-vary delay. Nonlinear controllers should be used to obtain good performances. However, the simple structure and the high reliability of fine tracking controllers should be guaranteed first, since the on-orbit maintenance would be ludicrously expensive. In order to resolve the contradiction, the fuzzy PID control for the fine tracking system is investigated based on the T-S (Takagi-Sugeno) control theory. Firstly, the T-S fuzzy model with time-varying delay is established to precisely reflect the dynamic characteristics of the fine tracking system. Secondly, the problem of designing fuzzy PID controllers to satisfy performance indexes is studied based on linear matrix inequalities. Thirdly, the information of the membership functions is brought into the controller design procedure to reduce the conservatism. At last, the experiment platform is built to test the disturbance suppression capability of the fine tracking system and its influence on the communication error rate.

相比于传统的微波通信，卫星光通信具有超高速数据传输、信息保密性好、功耗低等诸多优点。当激光通信链路建立后，卫星平台振动成为影响通信质量的关键因素。因此，要求卫星光通信终端的精跟踪系统具有很强的干扰抑制能力。一方面，精跟踪系统由压电陶瓷驱动的快速倾斜镜和CCD探测器组成，是一种典型的变时滞非线性系统，需要采用非线性控制器获得良好的抗干扰性能。另一方面，精跟踪系统在轨维护成本高，首选结构简单、可靠性高的控制器。为了解决上述矛盾，本项目基于T-S（Takagi-Sugeno）模糊控制理论，研究精跟踪系统的模糊PID控制器设计问题。首先，建立能够反映精跟踪系统动态特性的变时滞T-S模糊模型；其次，基于线性矩阵不等式，研究满足性能要求的模糊PID控制器设计问题；再次，将隶属度函数的信息引入到控制器设计之中，以降低设计的保守程度；最后，搭建实验平台，验证精跟踪系统的抗干扰能力及其对通信误码率的影响。

随着信息高速公路的不断发展，采用基于自由空间光通信的卫星激光通信技术越来越受到人们的关注，它具有信息容量大、保密性好等优点。类似于光纤通信技术，卫星激光通信是以光为信息载体实现通信的收发功能。光纤通信是由光纤作为通信光束传播的介质，而卫星激光通信则是以自由空间作为光束传播的介质。因此，通信光束容易受到自由空间中大气湍流、卫星平台振动等影响。这些影响使得通信光束不能够准确地入射到通信元件的光敏面上，降低了通信质量。.为了补偿大气湍流、卫星平台振动等因素的影响，卫星激光通信终端利用其上的精跟踪系统完成通信光束的对准。精跟踪系统由压电陶瓷偏摆镜和光斑探测器组成，光斑探测器实时监控光斑位置，然后控制器根据目标位置与实际位置的偏差计算控制量，驱动压电陶瓷偏摆镜偏转，使得光斑时刻保持在最佳通信点。可以看到，精跟踪系统对保证通信链路的稳定性具有重要意义。在本项目的资助下，我们针对精跟踪系统的各个环节进行了深入研究。精跟踪系统中的压电陶瓷偏摆镜具有迟滞效应，无法对其转动角度进行精确地控制，因此对压电陶瓷偏摆镜运动规律的深入了解具有非常重的意义。首先，本项目提出了一种快速补偿迟滞效应的方法，称之为轨迹直接建模法，该方法利用Madelung规则直接构建迟滞输出轨迹。其次，针对光斑探测器的时延问题，提出了一种光斑快速定位方法，从频谱域上快速匹配光斑信息，具有精度高、速度快的优点，有效地降低了时延的影响。进一步，我们为精跟踪系统分别设计了线性和T-S模糊控制器，使通信光斑快速准确地保持在理想位置。最后，我们搭建了精跟踪系统性能测试平台。本项目的迟滞补偿和控制方法直接应用于实践十三号卫星星地激光通信试验，保证了该试验的圆满成功。