匹配机械弹性车轮的电子稳定控制器参数分析

为了提高匹配机械弹性车轮(MEW)的某越野车操纵稳定性，考虑MEW与传统子午线轮胎侧偏特性存在的不确定性摄动，基于Lyapunov稳定性理论为电子稳定控制(ESC)程序设计了鲁棒反馈控制器；引入轮胎侧偏刚度不确定性的范数有界模型，运用Schur补引理和线性矩阵不等式(LMI)求解反馈矩阵。设定不同的车速和路面附着系数，通过搭建CarSim/Simulink联合仿真平台对控制器展开鱼钩试验，仿真结果表明，匹配MEW的ESC控制器能够保证车辆行驶的稳定性，横摆角速度与质心侧偏角跟踪误差分别稳定在0.03~0.3 rad/s与0.06~0.1 rad之内，并且设计的控制算法对MEW在05倍普通充气车轮侧偏刚度变化范围内具有很好的鲁棒性，从而为匹配MEW的整车主动安全控制提供了理论参考。     

Robust stability analysis and improved design of phase‐locked loops with non‐monotonic nonlinearities: LMI‐based approach

Due to nonlinear nature of several phase detectors, linear approximation method often leads to performance degradation in many phase‐locked loops (PLLs), particularly when the phase errors are sufficiently large. A third or higher order PLL, in spite of the ability to track a wider variety of inputs and having higher operating‐frequency range, requires more design attention in order to ensure stable tracking. In this work, with the nonlinearities inserted into the system's model, suitable criteria that take into account the nonlinearities' non‐monotonicity, sector and slope bounds are employed to establish robust stability conditions. The result is applicable to any PLLs without order and type restrictions. For Type‐1 PLLs, the resulting condition can be used to search for the maximum stable loop gain, which is also linked to the lock‐in range of the system. In the later part of this work, the focus is devoted towards designing PLLs with high lock‐in range, which is performed via mixing the proposed method with H _∞ synthesis. The searches for the parameters in both PLL analysis and design are expressed in terms of convex linear matrix inequalities, which are computationally tractable. To illustrate the improvement introduced via this approach, several numerical examples and simulations are included with comparisons over conventional methods. Copyright © 2017John Wiley & Sons, Ltd.     

Robust Stability of Networked Load Frequency Control Systems with Time-Varying Delays

In deregulated power system scenario coupled with smart grid technology, for networked load frequency control (LFC), an open communication structure, owing to low cost and flexibility, is preferred over dedicated networks in the feedback control loop for transmitting/receiving the data between the geographically displaced power system and the control center. In such a control scheme, closing the feedback loop through an open communication channel, in turn, introduces two additive time-varying delays of dissimilar characteristics in the feedback path. These delays degrade the performance of the closed-loop system, and exert a destabilizing effect on the overall system. In this paper, using Lyapunov-Krasovskii functional approach, a less conservative stability criterion is presented to ascertain delay-dependent stability of such network-controlled LFC systems with two additive time-varying delays in the feedback path in the presence of uncertain load disturbance conditions. Unlike the existing results, which are derived by combining these two delays into one, the proposed result considers the two delays as separate entities thereby imparting more generalization into the stability analysis. The effect of unknown exogenous load disturbance is incorporated by mathematically modeling them as a bounded non-linear time-varying function of current and delayed state vectors.     

含非线性扰动的混合变时滞中立系统鲁棒稳定性新判据

中立型时滞系统在工程实际中有着广泛应用背景.本文研究了一类含非线性扰动的混合变时滞中立型系统地鲁棒稳定性问题.基于直接Lyapunov泛函方法,通过构造一类新的包含时滞区间上下界的三重积分项Lyapunov-Krasovskii泛函,并结合积分不等式方法、自由权矩阵技术和凸组合处理方法,建立了一种新的线性矩阵不等式形式的离散时滞和中立时滞均相关的鲁棒稳定性判据.最后,通过数值算例验证了新判据的有效性和优越性,和一些已有文献相比,本文提出的判据具有更低的保守性.     

Feedback linearization via state transformation using estimated states

This paper deals with the exact feedback linearization of nonlinear plants using estimated states. Under appropriate hypotheses, exact linearization can be achieved through transformation of states and feedback. We assume that the states cannot be measured so that a nonlinear observer, with exponential convergence, is included in the loop. We establish sufficient conditions to guarantee that the overall system trajectories asymptotically converge to those obtained with feedback linearization utilizing the true states. We apply our results to control an electrical drive using a permanent-magnet synchronous motor without mechanical and optical sensors. The behaviour of our control scheme is illustrated by simulations.     

Equivalence of quadratic performance criteria†

Two quadratic cost functionals are defined to be equivalent, if they generate the same optimal control law. Necessary and sufficient conditions are derived in terms of the system parameters and the quadratic weighting matrices for two cost functionals to be equivalent.     

LMI‐based adaptive output feedback fault‐tolerant controller design for nonlinear systems

This paper presents 2‐novel linear matrix inequality (LMI)‐based adaptive output feedback fault‐tolerant control strategies for the class of nonlinear Lipschitz systems in the presence of bounded matched or mismatched disturbances and simultaneous occurrence of actuator faults, including failure, loss of effectiveness, and stuck. The constructive algorithms based on LMI with creatively using Lyapunov stability theory and without the need for an explicit information about mode of actuator faults or fault detection and isolation mechanism are developed for online tuning of adaptive and fixed output‐feedback gains to stabilize the closed‐loop control system asymptotically. The proposed controllers guarantee to compensate actuator faults effects and to attenuate disturbance effects. The resulting control methods have simpler structure, as compared with most existing recent methods and more suitable for practical systems. The merits of the proposed fault‐tolerant control scheme have been verified by the simulation on nonlinear Boeing 747 lateral motion dynamic model subjected to actuator faults.