Underactuated spacecraft angular velocity stabilization and three-axis attitude stabilization using two single gimbal control moment gyros

Angular velocity stabilization control and attitude stabilization control for an underactuated spacecraft using only two single gimbal control moment gyros （SGCMGs） as actuators is investigated. First of all, the dynamic model of the underactuated spacecraft is established and the singularity of different configurations with the two SGCMGs is analyzed. Under the assumption that the gimbal axes of the two SGCMGs are installed in any direction, and that the total system angular momentum is not zero, a state feedback control law via Lyapunov method is designed to globally asymptotically stabilize the angular velocity of spacecraft. Under the assumption that the gimbal axes of the two SGCMGs are coaxially installed along anyone of the three principal axes of spacecraft inertia, and that the total system angular momentum is zero, a discontinuous state feedback control law is designed to stabilize three-axis attitude of spacecraft with respect to the inertial frame. Furthermore, the singularity escape of SGCMGs for the above two control problems is also studied. Simulation results demonstrate the validity of the control laws.

Misalignment Angle Calculation Accuracy Analysis of Three-Axis Stabilized Geostationary Satellite

The most challenging problem of navigation in three-axis stabilized geostationary satellite is accurate calculation of misalignment angles, deduced by orbit measurement error, attitude measurement error, thermal elastic deformation, time synchronization error, and so on. Before the satellite is launched, the misalignment model must be established and validated. But there were no observation data, which is a non-negligible risk of yielding the greatest returns on investment. On the basis of misalignment modeling using landmarks and stars, which is not available between different organizations and is developed by ourselves, experimental data are constructed to validate the navigation processing flow as well as misalignment calculation accuracy. In the condition of using landmarks, the maximum misalignment calculation errors of roll, pitch, and yaw axis are 2, 2, and 104 micro radians, respectively, without considering the accuracy of image edge detection. While in the condition of using stars, the maximum errors of roll, pitch, and yaw axis are 1, 1, and 3 micro radians, respectively, without considering the accuracy of star center extraction. Results are rather encouraging, which pave the way for high-accuracy image navigation of three-axis stabilized geostationary satellite. The misalignment modeling as well as calculation method has been used in the new generation of geostationary meteorological satellite in China, FY-4 series, the first satellite of which was launched at the end of 2016.

Research on the Stability Control Strategy of Four-Wheel Independent Driving Electric Vehicle

In order to research stability of four-wheel independent driving (4WID) electric vehicle, a torque allocation method based on the tire longitudinal forces optimization distribution is adopted. There are two layers in the controller, which includes the upper layer and the lower layer. In the upper layer, according to the demand of the longitudinal force, PID controller is set up to calculate the additional yaw moment created by yaw rate and side-slip angle. In the lower layer, the additional yaw moment is distributed properly to each wheel limited by several constraints. Carsim is used to build up the vehicle model and MATLAB/Simulink is used to build up the control model and both of them are used to simulate jointly. The result of simulation shows that a torque allocation method based on the tire longitudinal forces optimization distribution can ensure the stability of the vehicle.

ROBUST STABILITY CRITERIA FOR SYSTEM WITH DELAY & ITS APPLICATION TO FCS

A study is devoted to the delay robust stability for linear system with time delay, using matrix analysis and comparison theory on differential integral difference equations. Since the matrix norm used to derive the results may be arbitrary consistent matrix norm, the obtained results possess some agility, and it makes quite convenient to check stability for linear systems with time delay. In particular, a sufficient and necessary condition for delay robust stability is obtained, and a formula to calculate the maximum delay for systems with stability is given. At the end, the results are used to analyze a flight control system (FCS). Comparison with some literature shows that the criteria in this paper are not only simple, but also of small conservativeness.

Stability of a delayed predator prey model in a random environment

The stability of the first-order and second-order solution moments for a Harrison-type predator-prey model with parametric Gaussian white noise is analyzed in this paper. The moment equations of the system solution are obtained under Ito interpretations. The delay-independent stable condition of the first-order moment is identical to that of the deterministic delayed system, and the delay-independent stable condition of the second-order moment depends on the noise intensities. The corresponding critical time delays are determined once the stabilities of moments lose. Further, when the time delays are greater than the critical time delays, the system solution becomes unstable with the increase of noise intensities. Finally, some numerical simulations are given to verify the theoretical results.

Stabilization of discrete-time linear systems by delay independent truncated predictor feedback

For a discrete-time linear system with input delay, the predictor feedback law is the product of a feedback gain matrix with the predicted state at a future time instant ahead of the current time instant by the amount of the delay, which is the sum of the zero in put solution and the zero state solutio n of the system. The zero state solution is a finite summation that involves past in put, requiring considerable memory in the digital implementation of the predictor feedback law. The truncated predictor feedback, which results from discarding the finite summat沁n part of the predictor feedback law, reduces implementation complexity. The delay independent truncated predictor feedback law further discards the delay dependent transition matrix in the truncated predictor feedback law and is thus robust to unknown delays. It is known that such a delay independent truncated predictor feedback law stabilizes a discrete-time linear system with all its poles at z = 1 or inside the unit circle no matter how large the delay is. In this paper, we first construct an example to show that the delay independent truncated predictor feedback law cannot compensate too large a delay if the open loop system has poles on the unit circle at z ≠ 1. Then, a delay bound is provided for the stabilizability of a general linear system by the delay independent truncated predictor feedback.

Stability criteria for linear systems with multiple time-varying delays

New delay-independent and delay-dependent stability criteria for linear systems with multiple time-varying delays are established by using the time-domain method. The results are derived based on a new-type stability theorem for general retarded dynamical systems and new analysis techniques developed in the author's previous work. Unlike some results in the literature, all of the established results do not depend on the derivative of time-varying delays. Therefore, they are suitable for the case with very fast time-varying delays. In addition, some remarks are also given to explain the obtained results and to point out the limitations of the previous results in the literature. Keywords Stability - Delay-independent criteria - Delay-dependent criteria - Linear time-delay systems - Multiple time-varying delays This work was supported by NSFC Key-Project (No. 60334010) and Guangdong Province Natural Science Foundation of China (No. 31406).

Independence and Accountability of Central Banks With a Special Focus on India

According to the consensus view, central banks reached a high level of independence by the end of last century. This paper argues that as a result short-term political considerations applied during the appointment process of central bank decision-makers, their actual independence was at a lower level already that time. The global f＇mancial crisis created new tasks for central banks and forced a review of the meaning of independence. The paper argues that central banks should be responsible for safeguarding fmancial stability and their macro-prudential activity can only be executed in cooperation with governments. However, interest rate policy decisions must remain free of political influence. The novelty of this paper lies in showing the conflictual relationship of the various roles of central banks. The paper concludes that the duality of independence and cooperation represents a major uncertainty in the operation of central banks. As a result of the greater degree of politicisation of the activities of central banks, their de facto independence in interest rate policy making may further shrink in the future. The paper also shows that India represents a unique case of central bank independence. In most countries, de jure independence is higher than de facto. India is one of the very rare countries where the reverse is the case.

具有独立缓冲结构的PDC—牙轮复合钻头研制

油气勘探开发过程中,难钻地层钻井效率低、钻头寿命短是影响深井、超深井钻井周期和成本的瓶颈问题。钻头工作过程中切削结构轮流与井壁接触而产生的多边形效应是导致钻头不稳定工作、切削齿冲击失效的主要因素。为提高钻头工作稳定性,提出了具有独立缓冲结构的PDC—牙轮复合钻头新结构,并针对四川盆地茅口组Ø311.2 mm井段常规PDC钻头冲击失效严重的问题,设计了3+3+3型(3个主刀翼、3个牙轮以及3个独立缓冲刀翼)的独立缓冲结构复合钻头,开展了全尺寸钻头室内钻进对比实验,并在川渝页岩气区块茅口组—栖霞组地层进行了实钻应用。研究结果表明:①独立缓冲结构复合钻头在常规复合钻头的牙轮切削结构和固定切削结构之间的空隙部位增设独立缓冲刀翼,有效缓解了多边形效应,对PDC齿形成很好的缓冲保护,同时分担了过大的钻压,限制了切削齿吃入深度,进而防止了钻头产生粘滑振动;②独立缓冲结构复合钻头钻压和扭矩波动小,扭矩为PDC钻头的1/5;③独立缓冲结构复合钻头取得了单只钻头进尺170 m的记录,比邻井同层位单只PDC钻头最高进尺提高了73.5%。结论认为,独立缓冲刀翼对提高钻头的稳定性起到了关键作用,不仅提高了钻头寿命,而且有效提高了复杂难钻地层及复杂结构井的综合钻井时效,有效降低了油气勘探开发成本。

分布式驱动车辆操纵稳定性控制综述

为研究分布式驱动车辆的驱动控制问题,从转向控制、独立驱动控制及2个系统联合控制等3个角度入手,分析了分布式驱动车辆操纵稳定性控制策略的研究进展。首先,基于转向控制技术对影响操纵稳定性的方面进行分类;其次,分析了分层式与集中式控制结构的特点;然后,分析了基于控制结构的操纵稳定性研究;最后,结合分布式驱动车辆操稳性改善的研究现状和技术进展,展望了未来的发展趋势。

五姿态轮椅设计与试验研究

针对国内的轮椅使用者在室内独立生活中面临的双手控制空间较小以及姿态转换稳定性不佳等问题,本文设计了一种融合五种姿态、具备高稳定性和可靠性的多姿态轮椅。基于人体工程学和可靠性工程学,设计了两种适用于小空间且具备高力矩的传动模块。通过对连杆模块进行运动学分析,验证了机构设计的合理性和稳定性。最后,利用姿态传感器对轮椅的姿态变换稳定性和静态刚度进行了测试。结果表明:该五姿态轮椅能够实现五种姿态的平稳变换,扩大了使用者的双手控制空间,并具备较高的静态刚度,能够满足下肢行动不便者独立生活的需求,提升了其独立生活的能力和生活质量。

基于滑模协调控制的四轮独立电驱动车辆稳定性控制研究

针对四轮独立电驱动车辆动力学特性及驱动控制策略复杂等问题,提出了基于力矩分配系数法的驱动协同控制策略,并设计了驱动力矩滑模协调控制器,配合车辆失稳判断模块计算出车辆维持稳定所需的附加横摆力矩,同时利用载荷分配方法设计了驱动力矩最优分配控制器,基于载荷分配方法将驱动力矩分配至4个车轮,以维持车辆稳定行驶。为验证驱动协同控制策略的有效性,基于CarSim软件建立四轮独立电驱动车辆模型,并将提出的驱动协同控制策略和普通滑模控制策略进行仿真对比。结果表明:驱动协同控制策略使横摆角速度偏差降低了25%,质心侧偏角偏差降低了23%,能够满足车辆稳定性控制要求,同时降低了整车驱动力矩分配控制难度。

SOC自适应调节的独立电网混合储能优化配置方法

针对高比例新能源接入独立电网后容易出现的频率稳定和功率波动问题,提出一种荷电状态自适应调节的混合储能优化配置方法。首先,基于对高比例新能源系统动态频率特性的分析,从频率稳定方面计算储能最小支援功率;然后,考虑系统对新能源出力波动的平抑需求,以经济性最低为目标函数,建立储能全寿命周期优化配置模型,并根据功率支援需求对荷电状态下限进行自适应调节;最后,以某高风电渗透率独立电网为例,验证所提策略的正确性和有效性。结果表明,所提方法兼顾系统频率稳定性与平滑新能源出力的需求,显著降低储能配置成本,具有更优的技术经济性。

Integrated energy-oriented lateral stability control of a four-wheelindependent-drive electric vehicle

Improving the energy efficiency of an electric vehicle(EV) is an effective approach to extend its driving range. This paper proposes an integrated energy-oriented lateral stability controller(IESC) for a four-wheel independent-drive EV(4 WID-EV) to optimize its energy consumption while maintaining vehicular stability during cornering. The IESC is a hierarchical controller with two levels. The high-level decision-making controller determines the virtual control inputs, i.e., the desired additional yaw moment and total wheel torque, while the low-level controller allocates the motor torques according to the virtual control inputs.In the high-level controller, the desired additional yaw moment is first calculated using a linear quadratic regulator(LQR) to minimize the control expenditure. Meanwhile, a stability weighting factor(SWF) based on phase plane analysis is proposed to adjust the additional yaw moment, which can reduce the additional energy consumption caused by the mismatch between the reference model and the actual vehicle. In addition to the yaw moment, the desired total wheel torque is calculated using a proportional-integral(PI) controller to track the desired longitudinal velocity. In the low-level controller, a multi-objective convex-optimization problem is established to optimize the motor torque by minimizing the energy consumption and considering the tire-road frictional limit and motor saturation. A globally optimal solution is obtained by using an active-set method. Finally,double-lane change(DLC) simulations are conducted using Car Sim and MATLAB/Simulink. The simulation results demonstrate that the proposed controller achieves great lateral stability control performance and reduces the energy consumption by5.23% and 2.95% compared with the rule-based control strategy for high-and low-friction DLC maneuvers, respectively.

稳定的光谱不随电流变化而改变的白色有机发光器件

使用新材料构成了两种结构白色有机薄膜电致发光器件 ,一种是蓝色及红色发射在同一层中 ,另一种是蓝色发射和红色发射分别在两层中 ,器件结构分别为ITO/CuPc/NPB/JBEM(P)∶DCJT/Alq/MgAg(器件 1 )和ITO/CuPc/NPB/JBEM(P) /Alq∶DCJT/Alq/MgAg(器件 2 )。这里Copperphthalocyanine(CuPc)是空穴注入层 ;N ,N’ bis ( 1 naphthyl) N ,N’ diphenyl 1 ,1’biphenyl 4 4’ diamine(NPB)是空穴传输层 (HTL) ;9,1 0 bis( 3’5’ diaryl) phenylanthracene(JBEM)是蓝色发射层[12 ] ;tris( 8 quinolinolato)aluminiumcomplex(Alq)是电子传输层 (ETL) ;DCJT是红色染料。在器件 1中得到稳定的且色度不随电流增大而变化的白色发射。它的最大亮度为 1 4 85 0cd/m2 ,最大效率 2 88lm/W ,色度x =0 31 ,y=0 38(从 4mA/cm2 到 2 0 0mA/cm2 ) ,半亮度寿命为2 86 0小时 (初始亮度 1 0 0 0cd/m2 )。比较了两种结构的器件 ,蓝红色发射在同一层结构的器件 ,在亮度。

Peabody运动发育量表2干预方案结合核心稳定性训练对痉挛型偏瘫的脑性瘫痪患儿上肢功能及运动功能独立性的影响

目的:探讨PDMS-2干预方案结合核心稳定性训练对痉挛型偏瘫的脑瘫患儿上肢功能及运动功能独立性的影响。方法:将60例痉挛型偏瘫的脑瘫患儿随机分为常规组、训练组、干预组,每组均20例,分别于治疗前及治疗3个月后、6个月后进行下列评估:Peabody精细运动发育量表(PDMS-2 FM)、改良Ashworth、儿童功能独立性评定量表(Wee FIM)运动功能项。结果:(1)PDMS-2 FM:治疗3个月后,常规组、训练组、干预组评分均较本组治疗前增加,差异均有显著性意义(P=0.015,0.001,0.000),干预组、训练组评分均较常规组增加,差异均有显著性意义(P=0.000,0.004),干预组、训练组间差异无显著性意义(P=0.390);治疗6个月后,常规组、训练组、干预组评分均较本组治疗3个月时增加(P=0.014,0.000,0.000),干预组评分较训练组增加,差异有显著性意义(P=0.007)。(2)改良Ashworth:各组治疗前后及治疗后同一测评点组间比较,差异均无显著性意义。(3)Wee FIM运动功能项:治疗3个月后,干预组、训练组评分均较本组治疗前增加,差异均有显著性意义(P=0.015,0.035),各组间比较差异无显著性意义;治疗6个月后,常规组、训练组、干预组评分均较本组治疗前增加,差异均有显著性意义(P=0.008,0.000,0.000),干预组、训练组评分均较本组治疗3个月增加,差异均有显著性意义(P=0.001,0.005),干预组、训练组评分均较常规组增加,差异均有显著性意义(P=0.002,0.045)。结论:PDMS-2干预方案结合核心稳定性训练能有效改善痉挛型偏瘫的脑瘫患儿上肢运动功能,促进精细运动发育,提高其运动功能独立性。

时滞系统的鲁棒稳定性分析

研究时滞系统的时滞独立稳定性和时滞相关稳定性问题。基于Ｂａｒｂａｌｅｔ引理，得到了一类检验线性时滞系统稳定性的简单条件。进一步研究了一类含非线性不确定性时滞系统的鲁棒稳定性问题。数值例子表明，所得到的结果比已有结果的保守性小。

基于ADAMS的双横臂扭杆独立悬架操纵稳定性分析

悬架的主要性能参数在悬架运动过程中的变化规律是影响悬架性能的主要因素。文章采用ADAMS软件建立了某商务车独立悬架的数学模型和仿真模型,分析了该悬架对操纵稳定性的影响,以及悬架主要性能参数的变化规律,为悬架设计奠定了基础。与传统的设计方法相比,这种方法提高了精度和效率。

独立驱动电动汽车稳定性的滑模变结构控制

为充分利用双电机独立驱动电动汽车两侧电机独立可控这个特点来提高车辆稳定性,在研究汽车动力学与稳定性特点的基础上,利用MATLAB/Simulink建立了包括任意路径下的单点预瞄驾驶员模型和"魔术公式"轮胎模型在内的8自由度的"人-车"闭环动力学仿真平台。运用滑模变结构控制原理,分别设计了以两侧电机为执行机构,以横摆角速度、质心侧偏角和横摆角速度与质心侧偏角联合为控制变量的3种等速趋近滑模变结构控制器,在仿真平台进行了稳定性控制的仿真。结果表明,3种控制器均可有效提高汽车极端工况下的操纵稳定性,其中,又以横摆角速度与质心侧偏角为联合控制变量的控制器效果最好。

C_(24)团簇结构与稳定性的理论研究

采用量子化学HF ,B3LYP和MP2方法 ,选用 6 3 1G ,6 3 11G ,cc pVDZ和cc pVTZ基组 ,对C2 4团簇的 6种异构体进行了优化 ,并对它们的几何构型、振动频率、核独立化学位移 (NICS)和稳定性进行了讨论 ,比较C2 4团簇各种异构体的稳定性 .研究表明 :在 6 3 11G 和cc pVDZ水平上 ,B3LYP方法给出的稳定性大小顺序分别为c >f >b >e >a >d和c >b >f >a >e >d ,MP2方法给出的稳定性大小顺序为b >c >a >e >f >d .