【作者】 郑燕红；

【导师】 陈兴林； 王岩；

【作者基本信息】 哈尔滨工业大学 ， 控制科学与工程， 2010， 博士

【摘要】 卫星激光通信是利用激光作为载波信号的一种重要的卫星通信方式,它是构成未来外层空间通信网络,星地通信网络的基础。本文结合卫星激光通信捕获、瞄准、跟踪过程,侧重研究了终端对对方终端位置的预测及搜索方案,针对对方光束位置提取过程中的图像处理问题,以及实现捕获瞄准跟踪过程的控制系统鲁棒稳定性、干扰抑制等问题进行了系统、深入地分析与设计:首先,针对激光通信链路的建立和保持过程,介绍了终端系统的各个组成单元,通过对典型终端机械结构及组成的分析,讨论了卫星激光通信终端系统的捕获、瞄准、跟踪过程以及相应的任务,并对扫瞄捕获过程中的捕获概率的约束因素进行了分析,通过对开关键控编码、曼彻斯特编码以及脉冲位置调制编码下的误码率大小进行了分析。其次,考虑到卫星平台轨道、姿态的运动对激光通信光束指向的影响和远距离通信过程中激光传输时间问题,采用坐标变换和直接建立相对运动微分方程组两种方案推导了摄动影响下的光通信终端天线的预测指向角,并对在轨卫星采用两种方案得到的预测指向角进行了仿真分析。由于在链路建立阶段需要通过扫瞄过程实现对目标的捕获,分析比较了三种扫瞄方案,提出了有效覆盖因子来表征单个光束投影的覆盖率,并结合预设重叠因子设计了常见扫瞄方式下的快速扫瞄与完全覆盖的扫瞄点放置方案,并获得了终端在扫瞄过程中应附加输入的扫瞄角变化规律,仿真显示确实能综合解决完全覆盖和快速完成扫瞄两个问题。再次,分析了探测器靶面上形成的光斑坐标与光束入射角的关系,并推导了终端天线和快速倾斜镜分别作为执行机构时相应的反馈角度提取方法。由于图像中混杂的噪声信号对光斑中心坐标计算有较大影响,提出了根据能量、面积的大小将灰度图象噪声分为孤立噪声点和恒星背景噪声两类进行滤波处理。在孤立噪声处理过程中提出了两种方案:一是利用Sobel算子结合梯度倒数形成动态模板加权平滑,然后通过最大类间方差法阈值分割实现噪声滤除;二是结合小波变换的时频局部性和神经网络的自学习能力,利用小波神经网络作为图像滤波器对噪声进行消除。而针对恒星背景噪声,提出了连通区域选择扩张方案和基于Canny算子边缘提取与K-均值聚类方案,对恒星背景噪声进行分离,结合孤立噪声与背景噪声滤波方法对灰度图像进行仿真处理,取得了良好的滤除效果。然后,针对光通信控制系统中终端天线与快速倾斜镜两个内回路的物理部件特性进行了分析,指出控制对象模型的不确定性;并分析了控制器由于量化误差、器件老化等因素可能引起的参数摄动;结合光通信系统的特点,总结了系统的内外部扰动信号,通过具体的仿真过程论证了扰动对系统的影响。针对终端天线回路的模型不确定性、控制器摄动和扰动信号的影响提出了鲁棒H∞控制器设计方法,对于快速倾斜镜回路由于时滞环节的影响,基于Lyapunov函数设计了时滞鲁棒H∞控制器,通过仿真分析验证了内回路对干扰和模型摄动的鲁棒性。最后,以终端天线与快速倾斜镜回路为基础构成了光通信捕获、瞄准、跟踪过程的捕获、瞄准阶段光通信终端控制系统,稳定性问题值得关注,基于终端天线与快速倾斜镜回路建立了光通信控制系统模型,通过时滞系统稳定性条件和矩阵测度稳定性条件分析了整个光通信控制系统的稳定性,并对终端天线与快速倾斜镜回路的设计进行了校验。为了完善整个设计过程,从时滞稳定性条件出发,采用公共的变换阵与锥补法推导了终端天线与快速倾斜镜回路鲁棒H∞状态反馈设计下确保整个系统稳定的约束设计方法。更多还原

【Abstract】 Satellite laser communication which use laser as carrier signal is an importantsatellite communication solution. It is a critical technology of space communicationnetwork, satellite-ground communication network.For the acquisition,pointing,tracking(APT) process of laser communication, such problems:predicting and searching for theobject terminal,image process for beam pointing angle recovery and robust control systemdesign were analyzed systematically and deeply in this dissertation.According to the process of establishing or keeping the laser communication link,thesubsystems of satellite communication terminal were introduced in detail. Basing on themechanic structure and optical scheme of canonical terminals,the work ?ow and taskof satellite laser communication terminal was divided into three partition.And then theconstraint factors for acquisition probability and the bit error rate with OOK, Manchesterand pulse position module were discussed.Considering the in?uence of satellite platform relative motion to communicationbeam and the beam transmit time because of long communication distance,coordinatetransform and Hill equation which usually describes the relative motion for two aircraft,were used to deduce the predicted pointing angle.And they were both verified in low orbitsatellites simulation.In the process of creating the communication link, scanning searchwas applied to capture the target terminal.The valid coverage factor and pre-overlappingfactor was proposed for coverage rate of projection beam. And then the least scanningpoint algorithm that can cover the uncertain area was induced based on the commonestscanning method.And the in?uence of valid coverage factor and pre-overlapping factorto acquisition time was analyzed. Simulation proves that entirely coverage and the leastscanning time problems can be resolved .The laser feedback loop offer the incident light from the joint terminal in anothersatellite.The terminal internal frame and fast steering mirror(FSM) frame were used todeduce the error angle of terminal antenna or FSM depending on spot center coordinate.The center coordinate calculated from gray image gathered by detector.And the imageinterfuses noise inevitably in the collection process,so the noise was divided into twocategories-isolated spot noise and stellar background noise in the light of noise area and power.Wavelet neural network filter and smoothing filter which connected with Sobeloperator and threshold method were proposed for isolated spot noise.Different from theisolated noise,the stellar background noise possess bigger area and energy, the selectionconnected region method and edge extraction were used for separating the valid spot andnoise spot.Through the combination of isolated noise filter and background noise filter,the simulation shows the gray image can offer better spot center coordinates.Moreover,the actuators for laser communication control system, brush-less directcurrent(BLDC) motor for terminal antenna loop and piezoelectric ceramics for FSM loop,were discussed. And the analysis result show the uncertainty of normal models.Whencontroller perturbation which caused by chip aging and analogical to digital convertererror appears, the analysis indicates that may arise some parameter variable.The inner andexternal disturbance were generalized for control system.And the in?uence of disturbanceto system task was simulated. Based on these points, robust H∞controller was designedfor terminal antenna loop and FSM loop which contains time delay unit.Simulation provedthat terminal antenna and FSM loop are robust for model perturbation and disturbance.Because the laser communication control system which composed by coarse loopand fine loop realizes APT process,the system stability become a focus.The whole APTsystem model was set up,and the stability condition was proposed under time delay systemstability theorem and matrix measure method. The design of terminal antenna and FSMloop was verified through the condition.In order to consummate the whole design process,common transform matrix was used to design the whole system stability.And then thecone complementary method transform the stability criterion to linear matrix inequalityconstraint.更多还原