深空探测天线自抗扰控制技术研究

随着深空探测技术的不断发展,深空探测设备天线口径的不断增大,观测频率越来越高,波束宽度越来越窄,这对天线伺服系统控制精度提出了很高的要求.深空探测天线伺服系统采用的PID控制是典型的被动抗扰设计,虽具有控制器结构简单、参数易于调整的优点,但抗扰能力不足的缺点,使其难以满足高精度指向和跟踪的需要.针对此问题,提出了基于自...     

Ka波段大型天线控制系统LQG控制器的设计

本文对国外Ka频段大型天线控制系统LQG位置控制器的研究方法与途径做了分析,针对天线控制系统性能要求高这一难点,提出了一个可行的方法,并利用Matlab软件包做了仿真实现.     

Ka波段大型天线控制系统LQG控制器的设计

对Ka频段大型天线控制系统LQG位置控制器的研究方法与途径作了分析，针对天线控制系统性能要求高这一难点，提出了一个可行的方法，并利用MATLAB软件包作了仿真实现。     

一种适用于北斗短报文通信的天线波束指向算法

针对北斗短报文通信中载体天线波束指向北斗卫星的问题,该文提出一种天线波束指向算法。该算法根据载体所处的地理位置和姿态,计算出指向北斗卫星的天线波束指向角。根据载体天线的合成波束增益和所处地理位置的北斗卫星波束增益,选择出最优的北斗卫星,并将天线波束指向该卫星。该方法可以保证载体运动过程中,天线合成波束实时指向最优北斗卫星,最大限度地提高了北斗短报文通信性能。     

一种适用于北斗短报文通信的天线波束指向算法

针对北斗短报文通信中载体天线波束指向北斗卫星的问题,该文提出一种天线波束指向算法.该算法根据载体所处的地理位置和姿态,计算出指向北斗卫星的天线波束指向角.根据载体天线的合成波束增益和所处地理位置的北斗卫星波束增益,选择出最优的北斗卫星,并将天线波束指向该卫星.该方法可以保证载体运动过程中,天线合成波束实时指向最优北斗卫星,最大限度地提高了北斗短报文通信性能.     

我国深空通信地球站天线系统研讨

根据我国深空探测发展需要，对我国深空通信地球站天线工作频率，口径尺寸选择等有关问题，进行了讨论，并对建议的３４ｍ天线系统给出了主要技术性能供研究。     

深空通信特点与关键技术分析

在讨论深空通信相关基本概念的基础上,对深空通信的特点进行了分析,并对适应于这些特点所涉及的关键技术进行了研究。着重阐述了阵列天线技术、高效调制解调技术、信道编码和传输层协议技术、信源编码和数据压缩技术、通信协议等技术的相关内容。研究认为,深空通信对我国航天事业的发展有着关键作用,将是今后通信技术的一个热点研究领域,并有可能带来新的技术上的突破。     

利用小推力实现与多颗小行星交会

小推力在深空探测中具有非常重要的意义.讨论了利用小推力实现航天器与多个小行星交会任务.小推力航天器与小行星的交会问题是一个标准的最优控制问题,文中将最优控制问题转化为参数优化问题,避免了求解最优控制问题所遇到的困难.首先利用遗传算法求解参数优化问题的全局最优解,然后利用局部优化算法对结果进行局部调节,提高交会精度.最后,以第二届国际轨道优化竞赛的题目为数值算例,给出了在小推力情况下航天器与四颗小行星交会的结果.结果表明该算法能很好地解决小推力航天器的交会问题.     

深空测控网的大口径天线与天线组阵

介绍了国外深空测控网的大口径天线和天线组阵技术和特点，分析了未来深空测控网发展中大口径天线与中小口径天线组阵的关系。     

单脉冲控制系统的设计和性能

Ka频段(32GHz)单脉冲跟踪系统已被选用到将来的NASA任务。这一决定要求在有噪声的环境下提高深空网天线伺服系统的指向精度。噪声源包括风载荷，编码器的机械误差以及接收机噪声。为了提高跟踪精度，本文对位置和单脉冲控制器的选用作了说明，同时给出了线性和非线性的仿真结果，以证实伺服系统的性能满足要求。     

Control systems of the large millimeter telescope

This paper presents the analysis results (in terms of settling time, bandwidth, and servo error in wind disturbances) of four control systems designed for the Large Millimeter Telescope (LMT). The first system, called PP, consists of the proportional and integral (PI) controllers in the rate and position loops, and is widely used in the antenna and radio telescope industry. The analysis shows that the PP control system's performance is remarkably good when compared to similar control systems applied to typical antennas. This performance is achieved because the LMT structure is exceptionally rigid; however, it does not meet the stringent LMT pointing requirements. The second system, called PL, consists of the PI controller in the rate loop, and the linear-quadratic-Gaussian (LQG) controller in the position loop. This type of controller is implemented in the NASA Deep Space Network antennas, where pointing accuracy is twice that of the PP control system. The third system, called LP, consists of the LQG controller in the rate loop, and the proportional-integral-derivative (PID) controller in the position loop. This type of loop has not been yet implemented at known antennas or radio telescopes, but the analysis shows that its pointing accuracy is the ten times better than the PP control system. The fourth system, called LL, consists of the LQG controller in both the rate loop and the position loop. It is the best of the four, with accuracy 250 times better than the PP system. It is thus worth further investigation to identify implementation challenges for telescopes with high pointing requirements.     

Antenna control systems: from PI to H∞

This paper discusses the compensation of antenna-pointing errors following the analysis and retrofit of the NASA Deep Space Network antenna control systems. The desired high-frequency communications with spacecraft (at Ka-band) require improved pointing precision over lower-frequency communications (at X-band). The quality of the antenna drives (hardware), the control algorithm (software), and the physical structure of the antenna (in terms of thermal deformations, gravity distortions, encoder mounting, and wind gusts) all influence pointing precision, and create the challenging task of remaining within the required pointing-error budget. Three control algorithms-PI (proportional-and-integral), LQG (linear-quadratic-Gaussian), and H_∞-are discussed, and their basic properties, tracking precision, and limitations as applied to antenna tracking are addressed. The paper shows that the PI algorithm is simple and reliable, but its performance is limited. It also explains how significant improvements in tracking precision are achieved when implementing the LQG control algorithm or the H_∞ control algorithm. Still, pointing precision attributable to software modification is limited. It is pointed out that an additional increase of tracking precision requires concurrent improvements in the antenna drives     

Optimal Controller for Stochastic Polynomial Systems with State-Dependent Polynomial Input

This paper presents an optimal quadratic-Gaussian controller for stochastic polynomial systems with a state-dependent polynomial control input and a quadratic criterion over linear observations. The optimal closed-form controller equations are obtained using the separation principle, whose applicability to the considered problem is substantiated. As an intermediate result, the paper gives a closed-form solution of the optimal regulator (control) problem for polynomial systems with a state-dependent polynomial control input and a quadratic criterion. Performance of the obtained optimal controller is verified in an illustrative example against a conventional linear-quadratic-Gaussian (LQG) controller that is optimal for linearized systems. Simulation graphs demonstrating overall performance and computational accuracy of the designed optimal controller are included.     

Using Stabilizer Dynamic Pre-Compensator to Design Robust Controllers for an Unstable MIMO System

This paper addresses the problem of designing LQG/LTR controllers for unstable multivariable systems. Its main proposal is to design a stabilizer dynamic pre-compensator to stabilize the system before designing the final LQG/LTR controller. This approach overcomes the problems that the This paper addresses the problem of designing LQG/LTR controllers for unstable multivariable systems. Its main proposal is to design a stabilizer dynamic pre-compensator to stabilize the system before designing the final LQG/LTR controller. This approach overcomes the problems that the original procedure can not avoid when it deals with unstable systems, but the order of the overall controller gets increased.     

Design of a general purpose 6-DOF haptic interface

A general purpose six degree-of-freedom haptic device is newly designed, which can be used as a general motion commander as well as a force reflector. The structure features the large workspace and easy analysis of a serial structure and the compactness and durability of a parallel structure at the same time. The study analyzed kinematics of the proposed device to obtain the optimal device parameters in terms of kinematics and derived dynamics to form a linear control system through the feedback. In calculating the optimal design factors of the haptic device in terms of kinematics, this study employed the global isotropy index. The proposed structure has high manipulability within the workspace, which is an essential factor for a motion generator. Also the study proposed a force controller featuring an inner nonlinear loop designed to compensate the nonlinear dynamics of the device and an outer linear control loop aimed to compensate un-modeled dynamics and disturbance. For an outer linear controller, the study adopted an LQG/LTR controller that can systematically take into account stability, robustness and frequency characteristics in the design process. The performance of the proposed device was verified with its efficiency through simulation and experiments.     

Foundations of Control and Estimation Over Lossy Networks

This paper considers control and estimation problems where the sensor signals and the actuator signals are transmitted to various subsystems over a network. In contrast to traditional control and estimation problems, here the observation and control packets may be lost or delayed. The unreliability of the underlying communication network is modeled stochastically by assigning probabilities to the successful transmission of packets. This requires a novel theory which generalizes classical control/estimation paradigms. The paper offers the foundations of such a novel theory. The central contribution is to characterize the impact of the network reliability on the performance of the feedback loop. Specifically, it is shown that for network protocols where successful transmissions of packets is acknowledged at the receiver (e.g., TCP-like protocols), there exists a critical threshold of network reliability (i.e., critical probabilities for the successful delivery of packets), below which the optimal controller fails to stabilize the system. Further, for these protocols, the separation principle holds and the optimal LQG controller is a linear function of the estimated state. In stark contrast, it is shown that when there is no acknowledgement of successful delivery of control packets (e.g., UDP-like protocols), the LQG optimal controller is in general nonlinear. Consequently, the separation principle does not hold in this circumstance     

Visuomotor optimality and its utility in parametrization of response

We present a method of characterizing visuomotor response by inferring subject-specific physiologically meaningful parameters within the framework of optimal control theory. The characterization of visuomotor response is of interest in the assessment of impairment and rehabilitation, the analysis of man--machine systems, and sensorimotor research. We model the visuomotor response as a linear quadratic Gaussian (LQG) controller, a Bayesian optimal state estimator in series with a linear quadratic regulator. Subjects used a modified computer mouse to attempt to keep a displayed cursor at a fixed desired location despite a Gaussian random disturbance and simple cursor dynamics. Nearly all subjects' behavior was consistent with the hypothesized optimality. Experimental data were used to fit an LQG model whose assumptions are simple and consistent with other sensorimotor work. The parametrization is parsimonious and yields quantities of clear physiological meaning: noise intensity, level of exertion, delay, and noise bandwidth. Significant variations in response were observed, consistent with signal-dependent noise and changes in exerted effort. This is a novel example of the role of optimal control theory in explaining variance in human visuomotor response. We also present technical improvements on the use of LQG in human operator modeling.     

LQG/LTR control of an AC induction servo drive

A new design method based on the linear-quadratic-Gaussian with loop-transfer-recovery (LQG/LTR) theory has been developed for the design of high performance AC induction servomotor drives using microcomputer-based digital control. The principle of field orientation is employed to achieve the current decoupling control of an induction motor. An equivalent model representing the dynamics of the decoupled induction motor has been developed. Based on the developed model with specified parameter uncertainties and given performance specifications, a frequency domain loop-gain-shaping method based on the LQG/LTR theory is proposed for the design of the servo loop controller. A microcomputer-based induction servomotor drive has been constructed to verify the proposed control scheme. Simulation and experimental results are given to illustrate the effectiveness of the proposed design method     

LQG-control of a highly resonant disk drive head positioningactuator

A fast fine-positioning controller has been designed for a rotary-actuator-type magnetic-storage disk drive. The controller was designed using the LQG (linear quadratic Gaussian) methodology and has been implemented on a digital signal processor. It is shown that LQG design is a viable approach, and that various problems associated with the structural resonances of the actuator can be solved     

Implementation of an Aerostat Positioning System With Cable Control

The capabilities of a multi-tethered aerostat positioning system are investigated using experimental and simulation results. The system consists of a platform supported by a helium-filled aerostat and attached to three anchored ground tethers actuated using computer-controlled winches. The experimental system was designed to perform a proof-of-concept study of a novel large-scale radio telescope requiring a receiver to be positioned accurately at an altitude of up to 500 m. Results from a series of flight tests are presented with a comparison between the passive response of the system and the response using proportional, integral, and derivative (PID) controllers with a position feedback. The motion of the platform is smaller for all cases using the feedback control. To improve on the PID results, a dynamics model of the system is used to develop and simulate optimal and feedforward (FF) control strategies. The optimal linear quadratic Gaussian (LQG) controller offers a 50% improvement over the PID controller, and both the LQG and the PID feedback controllers were shown to benefit considerably from the addition of a FF control term that exploits the measurements of the system's main disturbance force