Computer‐aided design methodology for linearity enhancement of multiwatt GaN HEMT amplifiers using multiple parallel devices

This article presents a design methodology for linearizing GaN HEMT amplifiers based on splitting a large FET into multiple parallel FETs with same total gate periphery and by biasing them individually. By varying the biases, the magnitude and the phase of the IMD3 components at the output of FET changes. A detailed simulation methodology using commercial microwave CAD software is presented. Simulation results show that by biasing one device in Class AB and other(s) in deep Class AB mode, IMD3 components of parallel FETs can be made out of phase to each other leading to cancellation and improvement in linearity. Three prototype circuits were simulated using (a) a single 5 mm FET (1 × 5 mm), (b) two parallel 2.5 mm FETs (2 × 2.5 mm), and (c) four parallel 1.25 mm FETs (4 × 1.25 mm), for a total gate periphery of 5 mm, over the frequency range of 0.8 to 1.0 GHz. IMD3 improvement up to 20 dBc was achieved with the 4 × 1.25 mm circuit when the FET biases were optimized. Measurement results show improvement in linearity up to 20 dBc for 4 × 1.25 mm circuit. The proposed method improves linearity without a substantial penalty on the power consumption and is straightforward to implement.     

高速率通信网络下时变系统的有限时域H∞控制

针对高速率通信网络和Round-Robin（RR）协议影响下网络化时变系统的有限时域[H∞]控制问题，考虑到系统中存在乘性噪声、随机时滞和量化效应，提出了一种基于观测器的有限时域[H∞]控制器的设计方法。利用李雅普诺夫稳定性理论和线性矩阵不等式（Linear Matrix Inequality，LMI）技术得到有限时域[H∞]控制器存在的充分条件。基于锥补线性化（Cone Complementarity Linearization，CCL）方法通过求解一组递归矩阵不等式得到观测器和控制器参数。所设计的控制器保证闭环网络化时变系统在给定的时域内稳定，且满足预定的[H∞]性能指标。数值仿真验证了所提方法的有效性。     

Attitude control of spacecraft simulator without angular velocity measurement

In this paper the attitude control of a spacecraft simulator using Reaction Wheels (RW) as the actuators is investigated. The main goal of the current study is to bring the RWs to the rest at the end of the maneuver without angular velocity measurement. A modified feedback linearization controller is applied by considering the Euler angles of the simulator as the output and the RWs angular momentums as the internal state variables. The stability of the proposed controller and the internal dynamics is analyzed using Lyapunov theory. Two modified sliding mode observers are designed to estimate the angular velocities of the spacecraft attitude control subsystem simulator. The proposed observers do not use the control input and the detailed knowledge of the model and thus it can be implemented easily. The global stability of the system is proved. The proposed controller and observers are finally evaluated numerically and experimentally on an attitude spacecraft simulator.     

Nonlinear model-based track guidance of user-defined points at the vehicle front

Preventive pedestrian protection systems are validated by means of fully automated driving tests reproducing safety-critical traffic situations on a proving ground. In order to assess these preventive safety systems, a precise and reproducible collision of a pedestrian dummy with a specific point at the vehicle front, e.g., the left corner of the vehicle, must be ensured. Hence, a track guidance of this specific point is required. Beyond the state of the art a new nonlinear model describing the lateral deviation of any point at the vehicle front to a predefined path is proposed in this paper. Based on this model the method of input–output linearization is used to design a flexible lateral guidance system for an easy application in different vehicles. Furthermore, the closed-loop stability is proven and experimental results are presented.     

Active disturbance rejection based trajectory linearization control for hypersonic reentry vehicle with bounded uncertainties

This paper investigates a novel compound control scheme combined with the advantages of trajectory linearization control (TLC) and alternative active disturbance rejection control (ADRC) for hypersonic reentry vehicle (HRV) attitude tracking system with bounded uncertainties. Firstly, in order to overcome actuator saturation problem, nonlinear tracking differentiator (TD) is applied in the attitude loop to achieve fewer control consumption. Then, linear extended state observers (LESO) are constructed to estimate the uncertainties acting on the LTV system in the attitude and angular rate loop. In addition, feedback linearization (FL) based controllers are designed using estimates of uncertainties generated by LESO in each loop, which enable the tracking error for closed-loop system in the presence of large uncertainties to converge to the residual set of the origin asymptotically. Finally, the compound controllers are derived by integrating with the nominal controller for open-loop nonlinear system and FL based controller. Also, comparisons and simulation results are presented to illustrate the effectiveness of the control strategy.     

测温铂电阻的非线性特性及线性化处理

本文详细分析了测温铂电阻的非线性特性和线性化方法，并给出了模拟电路线性化和ＥＰＲＯＭ表格线性化两种实用的线性化方案。     

悬架系统非线性元件对平顺性和道路友好性的影响

该文采用统计线性化法分析了货车悬架系统中两级变刚度复式钢板弹簧、液力减振器等非线性元件对车辆平顺性和道路友好性的影响. 试验结果表明考虑悬架系统非线性元件的影响时车辆振动状况的模拟值更接近实际情况.     

成层地基非线性波动问题人工边界与波动输入研究

建立了考虑非线性效应的无限成层地基波动模拟的时域人工边界条件及相应的波动输入方法。首先，推导了线性阻尼介质中的一维人工边界公式，进而推广得到近似的二维人工边界方程：然后，通过等效线性化处理，获得了近似考虑远场成层地基非线性效应的人工边界：最后，建立了相应的波动输入方法。数值算例表明，所给出的人工边界与波动输入方法具有良好的精度，可以方便地应用于成层地基非线性波动问题的研究。     

武汉长江隧道横断面地震响应分析

随着盾构法在隧道施工中越来越广泛的应用,其抗震性能的研究日益受到社会各界的关注.本文重点研究了武汉长江隧道工程盾构段横断面的地震响应规律.首先利用等效线性化方法对各典型地层构造处进行一维场地地震响应分析,以隧道所在土层的最大剪应变水平作为判断衬砌结构受力大小的依据,并选择危险控制断面.然后对该断面建立二维模型进行动力有限元计算,计算模型考虑了各类管片接头的影响及边界处能量的传输,能够有效地模拟土--结构系统的动力相互作用.计算表明在静力和地震共同作用下,隧道横断面的抗震性能满足要求.