Authors:Mahdianfar H; Prempain E. Abstract: To increase the performance of closed-loop controlled systems in off-nominal conditions and in the presence of inevitable faults and uncertainties, a systematic approach based on robust convex optimization for adaptive augmenting control design is discussed in this paper. More specifically, this paper addresses the problem of adaptive augmenting controller (AAC) design for systems with time-varying polytopic uncertainty. First, a robust state-feedback controller is designed via robust convex optimization as a baseline controller. The closed-loop polytopic system with the baseline controller is considered as the desired time-varying reference model for the design of a direct state-feedback adaptive controller. Next using Lyapunov arguments, global stability of combined robust baseline and adaptive augmenting controllers is established. Furthermore, it is proved that tracking error converges to zero asymptotically. A case study for a generic nonminimum phase nonlinear pitch-axis missile autopilot is conducted. Simulation tests are performed to evaluate stability and performance of nonlinear time-varying closed-loop system in the presence of uncertainties in pitching moment and normal force coefficients, and unmodeled time delays. In addition, results of the simulations indicate satisfactory robustness in case of severe loss of control effectiveness event. PubDate: Thu, 22 Sep 2016 00:00:00 GMT

Authors:Rakkiyappan RR; Lakshmanan SS, Lim CP. Abstract: This paper presents the synchronization criteria for two identical delayed chaotic Lur'e systems. Here, we employ network reliable feedback control for achieving synchronization between our considered systems. The advantage of the employed controller lies in the fact that it even works in the case of actuator or sensor failures, which may occur in many real-world situations. By introducing an improved Lyapunov–Krasovskii (L–K) functional and by using reciprocally convex technique, sufficient conditions are given in the form of linear matrix inequalities (LMIs) to ensure asymptotic stability of resulting synchronization error system. Numerical simulations of neural networks and Chua's circuit system are given to verify the effectiveness and less conservatism of the presented theoretical results. PubDate: Thu, 22 Sep 2016 00:00:00 GMT

Authors:Xian B; Zhao B, Zhang Y, et al. Abstract: In this paper, a new adaptive tracking controller is developed for a quadrotor unmanned aerial vehicle (UAV) via immersion and invariance (I&I) approach. The controller is able to compensate parametric uncertainties such as the unmeasurable effects of the deviated center-of-gravity (CoG), as well as the aerodynamic coefficients. The globally asymptotic tracking of the desired attitude trajectories is proven via the Lyapunov-based stability analysis and LaSalle's invariance theorem. Real-time experiment results performed on a quadrotor attitude control testbed are given to show the good control performance of the proposed scheme. PubDate: Fri, 09 Sep 2016 00:00:00 GMT

Authors:Rastgoftar H; Atkins EM. Abstract: A leader follower model has recently been proposed for homogeneous deformation of a multi-agent system (MAS) in ℝn. Researchers have shown how a desired homogeneous transformation can be designed by choosing proper trajectories for n + 1 leader agents and can be learned by every follower through local communication. However, existing work requires every follower to communicate with n + 1 adjacent agents, where communication between every two adjacent followers is constrained to be bidirectional. These requirements limit the total allowable number of agents, so an arbitrary number of agents may not be able to acquire a desired homogeneous mapping by local interaction. Additionally, if followers are not allowed to communicate with more than n + 1 neighboring agents, the convergence rate of actual positions to the desired positions (defined by a homogeneous transformation) may not be sufficiently high. The system may then considerably deviate from the desired configuration during transition. The main contribution of this article is to address these two issues, where each follower is considered to be a general linear system. It will be proven that followers can acquire desired positions prescribed by a homogeneous mapping in the presence of disturbance and measurement noise by applying a new finite-time reachability model under either fixed or switching topologies, if: (i) communication among followers is defined by a directed and strongly connected subgraph, (ii) each follower applies a consensus protocol with communication weights that are consistent with the positions of the agents in the initial configuration, and (iii) every follower i is allowed to communicate with mi≥n+1 local agents. With this strategy, an MAS with an arbitrary number of agents with linear dynamics can acquire a desired homogeneous mapping in the presence of disturbance and measurement noise, where convergence rate can be enhanced by increasing the number of communication links. PubDate: Fri, 09 Sep 2016 00:00:00 GMT

Authors:Ramani KS; Duan M, Okwudire CE, et al. Abstract: An approach for minimizing tracking errors in linear time-invariant (LTI) single-input single-output (SISO) discrete-time systems with nonminimum phase (NMP) zeros using filtered basis functions (FBF) is studied. In the FBF method, the control input to the system is expressed as a linear combination of basis functions. The basis functions are forward filtered using the dynamics of the NMP system, and their coefficients are selected to minimize the error in tracking a given desired trajectory. Unlike comparable methods in the literature, the FBF method is shown to be effective in tracking any desired trajectory, irrespective of the location of NMP zeros in the z-plane. The stability of the method and boundedness of the control input and system output are discussed. The control designer is free to choose any suitable set of basis functions that satisfy the criteria discussed in this paper. However, two rudimentary basis functions, one in time domain and the other in frequency domain, are specifically highlighted. The effectiveness of the FBF method is illustrated and analyzed in comparison with the truncated series (TS) approximation method. PubDate: Thu, 08 Sep 2016 00:00:00 GMT