横向联邦学习中PCA差分隐私数据发布算法

为了让不同组织在保护本地敏感数据和降维后发布数据隐私的前提下,联合使用PCA进行降维和数据发布,提出横向联邦PCA差分隐私数据发布算法。引入随机种子联合协商方案,在各站点之间以较少通信代价生成相同随机噪声矩阵。提出本地噪声均分方案,将均分噪声加在本地协方差矩阵上。一方面,保护本地数据隐私;另一方面,减少了噪声添加量,并且达到与中心化差分隐私PCA算法相同的噪声水平。理论分析表明,该算法满足差分隐私,保证了本地数据和发布数据的隐私性,较同类算法噪声添加量降低。实验从隐私性和可用性角度评估该算法,证明该算法与同类算法相比具有更高的可用性。     

Robots positioning control revisited

Positioning control systems for robot arms are presented within a general framework in view of unification and classification. Treating coupling torques from other links as an external disturbance reduces the design of the control system to that of SISO servomechanisms driving each of the robot axes individually. A short survey of many control strategies proposed in the literature presents them as different methods aiming at attenuation of this disturbance. The use of disturbance observers is shown to provide a nice and simple way for that purpose. This could be applied to the improvement of actual industrial robots at the cost of slight software modifications.     

Positive state‐bounding observer for positive interval continuous‐time systems with time delay

This paper is concerned with the problem of positive observer synthesis for positive systems with both interval parameter uncertainties and time delay. Conventional observers may no longer be applicable for such kind of systems due to the positivity constraint on the observers, and they only provide an estimate of the system state in an asymptotic way. A pair of positive observers with state‐bounding feature is proposed to estimate the state of positive systems at all times in this paper. A necessary and sufficient condition for the existence of desired observers is first established, and the observer matrices can be obtained easily through the solutions of a set of linear matrix inequalities (LMIs). Then, to reduce the error signal between the system state and its estimates, an iterative LMI algorithm is developed to compute the optimized state‐bounding observer matrices. Finally, a numerical example is presented to show the effectiveness and applicability of the theoretical results. Copyright © 2011 John Wiley & Sons, Ltd.     

Sliding mode control with disturbance observer for a class of nonlinear systems

This paper is concerned with the stabilization problem for a class of nonlinear systems with disturbance. The disturbance model is unknown and the first derivative of disturbance is bounded. Firstly, a general disturbance observer is proposed to estimate disturbance approximatively. Secondly, since the bound of the disturbance observer error is unknown, an adaptive sliding mode controller is designed to guarantee that the state of system asymptotically converges to zero and the unknown bound can be adjusted by an adaptive law. Finally, an example is given to illustrate the effectiveness of the proposed method.     

Observer‐based Reliable Control for Discrete Time Systems: An Average Dwell Time Approach

This paper deals with the problem of reliable control for discrete time systems with actuator failures. The actuator is assumed to fail occasionally and can recover over a time interval. During the time of suffering failures, the considered closed‐loop system is assumed unstable. Using an average dwell time method and under the condition that the activation time ratio between the system without actuator failures and the system with actuator failures is not less than a specified constant, an observer‐based feedback controller is developed in terms of linear matrix inequalities such that the resulting closed‐loop system is exponentially stable. An example is included to demonstrate the effectiveness of the proposed approach.     

Optimal Performance in Tracking Stochastic Signal Under Disturbance Rejection

The analysis method of optimal tracking performance is proposed for multiple‐input multiple‐output (MIMO) linear time‐invariant (LTI) systems under disturbance rejection. An H₂ criterion of the error signal between the output of the plant and the reference signal is used as a measure for the tracking performance. Spectral factorization is applied to obtain the optimal solution of the system tracking error. The explicit expressions are derived for this minimal tracking error with respect to random reference signals under disturbance rejection. It is shown that the nonminimum phase zeros, the zero direction, the unstable poles, the pole direction of a given plant, statistical characteristics of the reference input signal, and disturbance signal have a negative effect on a feedback system's ability to reduce the system error with disturbance rejection. The results show that the optimal tracking performance will further be damaged because of disturbance rejection. Some typical examples are given to illustrate the theoretical results.     

A new admissibility condition of discrete-time singular systems with time-varying delays

This paper gives a novel delay-dependent admissibility condition of discrete-time singular systems with time-varying delays. For convenience, the time-varying delay is assumed to be the sum of delay lower bound and the integral multiples of a constant delay. Specially, if the constant delay is of unit length, the delay is an interval-like time-varying delay. The proposed admissibility condition is presented and expressed in terms of linear matrix inequality (LMI) by Lyapunov approach. Generally, the uncertainty of time-varying delay would lead to conservatism. In this paper, this critical issue is tackled by accurately estimating the time-varying delay. Consequently, the proposed admissibility condition is less conservative than the existing results, which is demonstrated by a numerical example.     

线性系统的H2/H-故障检测优化方法设计

针对一类具有未知扰动的线性系统的故障检测(FD)问题,通过对系统进行重构,设计出了系统的H2/H-优化FD观测器。利用构造的Lyapunov函数和线性矩阵不等式,证明并给出了FD观测器有解的充分条件和优化设计方法。所设计的观测器使系统具有渐近稳定性,抑制干扰能力强,满足所给的范数指标。仿真结果验证了所设计方法的有效性。     

基于VGLESO和滑模理论的直流配电网母线电压控制策略

针对直流配电网母线电压稳定性问题,设计了一种变增益线性扩张状态观测器(variable gain linear extended state observer,VGLESO),有效地解决了传统高增益线性扩张状态观测器(linear extended state observer extended state observer,LESO)在运行初始阶段输出存在峰值的问题。在此基础上进一步提出了一种变增益滑模自抗扰控制策略,将其应用到直流配电网AC-DC双向变流器控制系统中的电压外环。变增益滑模自抗扰控制策略在不需要增加额外电流传感器的情况下,就能够实现对系统总扰动的快速跟踪和补偿,有效地抑制了母线电压波动,提高了系统的动态响应。从理论上证明了VGLESO和变增益滑模自抗扰控制策略的稳定性。最后通过MATLAB/Simulink验证了该控制策略的可行性与正确性。     

基于协同观测器的永磁同步电机无传感控制

针对传统滑模观测器使用符号函数引起的抖振问题,提出了一种基于连续函数的协同观测器方法,实现永磁同步电机(PMSM)的无传感控制。首先,研究PMSM的离散数学模型。其次,建立k+1时刻的电流偏差和k时刻的电流偏差之间的函数关系。最后,利用反正切函数计算转子位置并加入角度补偿,提高观测精度。仿真结果表明,所设计的协同观测器不仅无抖振现象,还具有更高的估算精度及良好的抗干扰性能,比传统滑模观测器可以更好地实现PMSM的无传感控制。