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This letter aims to investigate the robust stability of an interval fractional-order plant with an interval time delay by a general form of fractional-order controllers. Based on a simple graphical procedure, necessary and sufficient criteria are proposed to analyze the robust stability of an interval fractional-order plant. Then, the idea of “robust stability testing function” is extended to analyze the robust stability of the considered type of systems. Besides, an upper frequency bound is provided which is useful for the simulation purposes and it helps to reduce the computational cost. Finally, two examples are presented to verify the usefulness of the obtained results.

In this paper, the issue of string stability for acceleration-controlled vehicles interconnected in a chain is studied. String stability is concerned with having bounded displacements between vehicles in such a way that displacements should not grow unboundedly with respect to the perturbation. Different definitions can be given to string stability: one that relates to the amplification of a local disturbance acting on one vehicle toward the whole vehicle chain, more strict definition that is related to the boundedness of vector norm of displacements with respect to the bounded vector norm of disturbance inputs acting on all vehicles; and, most practical definition that considers the boundedness of signal norm of each individual displacement with respect to the bounded signal norm of disturbance inputs acting on all vehicles, independently from the number of vehicles. It has been proven that these definitions are all impossible to be achieved using any linear homogeneous unidirectional distributed controllers with constant spacing policy. This paper proposes linear heterogeneous controllers where each vehicle behaves differently from others in a vehicle chain. We prove that three different definitions of string stability can be attained using the proposed heterogeneous controller. We propose sufficient conditions to guarantee string stability and boundedness of acceleration of each vehicle. Finally, simulation results are given to illustrate the effectiveness of proposed heterogeneous control synthesis.

In this paper, a distributed controller is designed for the consensus of multi‐agent systems in which each agent has a general second‐order linear dynamic and the information is exchanged over a data‐delaying communication network. Using the sensitivity of system poles to the parameters of the control protocol, graphical delay‐dependent synthesis conditions are derived to tune the controller gains. A systematic procedure is developed to attain maximum tolerable transmission delay in the system. Moreover, simpler condition is provided for the special case where the second‐order model is reduced to a double integrator. Simulation results are presented to illustrate the merits of the proposed scheme compared to some recent rival ones in the literature.

In this paper the problem of synchronisation of multiple robotic manipulators using Hoo robust distributed control systems with respect to the parameter uncertainties and disturbance inputs acting on the manipulators is addressed. Robust synchronising controllers only use the information of outputs of the manipulators, and the corresponding parameters of these output-feedback controllers are designed by computing a series of linear matrix inequalities instead of solving the complex differential (e.g. Hamilton-Jacobi) (in)equalities. The proposed controller can guarantee H∞ robust performance with respect to the external disturbance inputs and parameters uncertainties, asymptotic stability and synchronisation in the networked manipulators. Using an illustrative example we compare the results extracted in this paper to other works existing in the literature.

This paper deals with the problem of string stability in a chain of acceleration-controlled vehicles, i.e. how input disturbances affect the distributed system for very long chains. There exist variants of string stability, like avoiding that a local disturbance gets amplified along the chain, or more strongly ensuring that the output vector's p-norm remains bounded for any bounded vector of input disturbances independently of the string length. They are all impossible to achieve with any linear controller if the vehicles only use relative information of few vehicles in front. Previous work has shown that adding absolute velocity into the controller, allows to at least avoid amplification of a local disturbance. In this paper, we consider the stronger definitions of string stability, under this same relaxation of using absolute velocity in the controller. We prove that the influence from input vector to output vector cannot be bounded independently of chain length in the most popular 2-norm sense, with any bounded stabilizing linear controller; while a proportional derivative (PD) controller can guarantee it in the practically relevant infinity-norm sense. Moreover, we identify the disturbance acting on the leader as the main issue for string stability., Comment: presented at IEEE-CDC 2018, Miami; more complete version and correcting a few typos

The interaction between the tyre and the road is crucial for understanding the dynamic behaviour of a vehicle. The road–tyre friction characteristics play a key role in the design of braking, traction and stability control systems. Thus, in order to have a good performance of vehicle dynamic stability control, real-time estimation of the tyre–road friction coefficient is required. This paper presents a new development of an on-line tyre–road friction parameters estimation methodology and its implementation using both LuGre and Burckhardt tyre–road friction models. The proposed method provides the capability to observe the tyre–road friction coefficient directly using measurable signals in real-time. In the first step of our approach, the recursive least squares is employed to identify the linear parameterisation form of the Burckhardt model. The identified parameters provide, through a T–S fuzzy system, the initial values for the LuGre model. Then, a new LuGre model-based nonlinear least squares parameter estimation algorithm using the proposed static form of the LuGre to obtain the parameters of LuGre model based on recursive nonlinear optimisation of the curve fitting errors is presented. The effectiveness and performance of the algorithm are demonstrated through the real-time model simulations with different longitudinal speeds and different kinds of tyres on various road surface conditions in both Matlab/Carsim environments as well as collected data from real experiments on a commercial trailer.

This paper deals with the problem of string stability of interconnected systems with double-integrator open loop dynamics (e.g. acceleration-controlled vehicles). We analyze an asymmetric bidirectional linear controller, where each vehicle is coupled solely to its immediate predecessor and to its immediate follower with different gains in these two directions. We show that in this setting, unlike with unidirectional or symmetric bidirectional controllers, string stability can be recovered when disturbances act only on a small (N-independent) set of leading vehicles. This improves existing results from the literature with this assumption. We also indicate that string stability with respect to arbitrarily distributed disturbances cannot be achieved with this controller.

This paper deals with the problem of stability of one dimensional vehicle chain with double integral terms. Disturbance inputs can affect the performance of vehicle chain and furthermore can lead to instability namely called string instability. It is proposed a distributed adaptive sliding mode control for each vehicle. In the proposed distributed adaptive sliding mode controller it is not necessary to know the value of upper and lower bounds of disturbance inputs. only the information of two successive vehicles in front is enough to implement the controller, this means that each vehicle is connected unidirectionally in the vehicle chain with no information of the following vehicles. We prove that with such condition it is possible to guarantee string stability in the vehicle chain. Furthermore, constant spacing error between the vehicles without using time headway policy, is used. The effectiveness of the proposed method is shown as well with simulation results.

This paper investigates the problem of stability analysis for a class of linear systems with interval time-varying delay. In order to develop a less conservative stability condition, a Lyapunov-Krasovskii functional comprising novel integral terms is introduced. Convex combination idea is utilized to derive a stability criterion in terms of linear matrix inequalities (LMIs) without any additional free-weighting matrices which increase drastically the computational burden of the stability test. Numerical examples are presented to illustrate the superiority of the proposed approach compared to some existing ones in the literature.

This note investigates the problem of exponential stability of neural networks with time-varying delays. To derive a less conservative stability condition, a novel augmented Lyapunov-Krasovskii functional (LKF) which includes triple and quadruple-integral terms is employed. In order to reduce the complexity of the stability test, the convex combination method is utilized to derive an improved delay-dependent stability criterion in the form of linear matrix inequalities (LMIs). The superiority of the proposed approach is demonstrated by two comparative examples.

We provide a comprehensive impossibility result toward achieving string stability, i.e., keeping local relative errors in check with local controllers independently of the size of a chain of subsystems. We significantly extend the existing results, from the linear time-invariant (LTI) setting to any homogeneous controllers that can be nonlinear, time varying, and locally communicating. We prove this impossibility for a set of definitions with various norm choices, including the $L_2$ -type standard and a bounded-input implies bounded-output (BIBO) type criterion. All the results hold for a general discrete-time controller, which should cover most applications.

International audience; This paper deals with the problem of string stability in a chain of acceleration-controlled vehicles. It is known that string stability cannot be achieved, with any linear controller, when the vehicles' control inputs are based only on relative distances to a fixed number of predecessors. We extend the set of characteristics under which string stability is impossible by including elements like dynamic sensor parts and local inter-vehicular communication, as in cooperative adaptive cruise control. It is also known that a weaker form of string stability is achievable by adding absolute velocity measurements (e.g. "time-headway" policy). We show that a stronger property can also be achieved, provided steady-state control gain is infinite e.g. by using integral control.

In this paper, real-time identification of the dry-clutch torque characteristics model in automotive systems is investigated. The proposed algorithm focused to provide the direct capability to update the clutch torque characteristics model by using engine speed and torque as measurable signals in real-time, within a multiple model predictive control loop. First, the clutch torque is estimated with some uncertainty. Then, it is proposed a new trust-region based identification approach which is robust enough to cover this uncertainty. The aim of the MPC controller is to ensure a comfortable lockup by avoiding engine stall and reasonable engagement time. The effectiveness and performance of the approach are demonstrated through the real-time model simulations in various conditions.

This paper investigates the problem of stability analysis and stabilization for networked control systems with the network-induced delay and data dropout. In order to obtain less conservative results, a novel augmented Lyapunov–Krasovskii functional is introduced and new free-weighting matrices are employed to make some extra degrees of freedom in the sufficient stabilizability condition. The gain of the memoryless state-feedback controller is computed by solving a set of linear matrix inequalities (LMIs). Illustrative examples are given to verify the applicability and outperformance of the proposed method compared to the existing approaches in the literature.

It is well recognized in the automotive research community that knowledge of the real-time tyre-road friction conditions can be extremely valuable for intelligent safety applications, including design of braking, traction, and stability control systems. This paper presents a new development of an on-line tyre-road adherence estimation methodology and its implementation using both Burckhardt and LuGre tyre-road friction models. The proposed strategy first employs the recursive least squares to identify the linear parameterization (LP) form of Burckhardt model. The identified parameters provide through a Takagi-Sugeno (T-S) fuzzy system the initial values for the LuGre model. Then, it is presented a new large-scale optimization based estimation algorithm using the steady state solution of the partial differential equation (PDE) form of LuGre to obtain its parameters. Finally, real-time simulations in various conditions are provided to demonstrate the efficacy of the algorithm.

This paper is concerned with the H ∞ controller design for robust stabilization of networked control systems with the network-induced delay, data packet dropout and norm-bounded parameter uncertainties. In order to obtain less conservative results, a new augmented Lyapunov-Krasovskii functional is used and novel free-weighting matrices are employed to make some extra degree of freedom in the H ∞ design conditions. The feedback gain of a memoryless controller, maximum allowable delay bound and minimum disturbance attenuation level can be derived by solving a set of linear matrix inequalities (LMIs). The advantages of the proposed method are demonstrated by numerical example.

This paper deals with the problem of the stability analysis and controller gain synthesis for networked control systems with the network-induced delay, data packet dropout, parameters' uncertainties and disturbance input. To achieve less conservative results compared with existing methods in the literature, a novel Lyapunov-Krasovskii functional is constructed and new free-weighting matrices are introduced to increase degrees of freedom in the sufficient robust stability conditions. The maximum allowable delay bound, minimum attenuation level and the gain of memoryless controller is obtained by solving a set of linear matrix inequalities (LMIs). Finally an illustrative example is given to reveal the effectiveness of the proposed approach.

This paper proposes a design approach to synthesis static state-feedback controller for Wheeled Mobile Robots (WMRs) controlled via a wireless communication networked. Variable delays considered in the Networked Control System (NCS) model to represent both of the data packet latency and dropout. Utilizing an appropriate Lyapunov-Krasovskii functional, an improved sufficient condition is derived to determine the controller gain in terms of Linear Matrix Inequalities (LMIs). Simulations demonstrate that the proposed method leads to remarkably less conservative results compared with the others' methods.

In this paper, a novel method is developed to control switched DC-DC Buck converters. The circuit dynamic is described as an affine linear switched system. Utilizing switched systems theory, a switching state-feedback law is derived to asymptotically stabilize the desired equilibrium point and also minimize a guaranteed cost. The efficiency of the proposed method is illustrated by simulation which verifies the improvement of the obtained results compared with the literatures.

Variable speed small to medium wind turbines need to cope with the intermittent nature of wind speed at lower altitudes. This imposes challenges on optimally tracking the maximum power point (MPP) during partial load and makes the wind turbine dynamics highly nonlinear. As a result, using one linear controller around a specific operating point may not guarantee acceptable performance in the other operating points. In addition, wind speed variations cause fluctuations in the output power of the turbine. The Soft Switching Multiple Model Predictive Control (SSMMPC) technique is introduced to tackle the latter problems when considering multiple linear models around various operating points (MPPs) approximating the nonlinear dynamics. The gap metric method is used to assess how close different linear models are with respect to each other. The closed loop system stability is validated using Lyapunov theory. The controller performance is investigated and compared with a bidirectional TSR-based controller through simulations using the FAST NREL 10kW wind turbine model. The results verify the improvements that can be attained by using SSMMPC in terms of higher maximum power point tracking quality, lower generator torque oscillations and smoother output power, consequently.

In this talk we are concerned with a new development of an on-line road condition monitoring methodology and its implementation using PDE form of LuGre tyre-road friction model. The road condition is recursively evaluated regarding slipperiness and is classified into three grades, normal (_ _ 1), i% slippery (1 < _ < 5), and mixed friction surface (_ is varying). The linearized tyre model parameters are estimated and then converted to the initial values of identification algorithm through the multivariate interpolation. An iterative parameter identification algorithm that utilizes steady state solution of the PDE form of LuGre, is used to identify the road condition parameters. In order to have a fast, robust and efficient identification algorithm, a minimizing quadratic function subject to an ellipsoidal constraint is considered, which is guaranteed to yield an optimal solution in a finite number of iterations. The talk is complemented by a performance report of the new algorithm for various road conditions. Our numerical testings are very promising and show the practical viability of the algorithm.