Online time delay estimation in networked control systems with application to bilateral teleoperation

The digital control system of modular multilevel converters (MMCs) normally synchronizes with the switching actions. The switching frequency of an MMC is generally selected as low as possible from an efficiency point of view, which leads to an unavoidable and relatively long time delay in the control system. Such a time delay might deteriorate the MMC performance and even reduce the stability margin by introducing infinite uncertain eigenvalues into the system state functions. Without a proper time-delay model and quantitative system stability analyses, MMCs might suffer from uncertainties and unstable risks during their operations, especially when the switching frequency is low. This paper derives an MMC model considering the time delay in the digital control system. A Pade-based stability analysis method is then proposed, which consists of three steps: information integration and critical eigenvalue extraction, and trajectory visualization and critical angle (CA) calculation, and quantitative assessment and extreme value determination. By the proposed model and method, the critical eigenvalue can be effectively extracted. With the Hopf bifurcation, the time delay in the digital control system induces a pair critical conjugate eigenvalues into MMC systems, which is detected as an instability cause. The CA and the critical impact are defined to quantitatively assess the stability, while selecting the controller parameters and minimum switching frequency. The proposed method for the MMC stability assessment is experimentally verified.

Network Control.- Delay-Based Non-linear Observers for Congestion Control in Communication Networks.- On the Use of State Predictors in Networked Control Systems.- Networked Control Systems: Algorithms and Experiments.- Modeling and Closed Loop Control for Resource-Constrained Load Balancing with Time Delays in Parallel Computations.- Stability of Load Balancing Control.- Teleoperation.- Robust H ? Control of Bilateral Teleoperation Systems Under Communication Time-Delay.- Web Remote Control of Mechanical Systems: Delay Problems and Experimental Measurements of Round Trip Time.- PDE Approach for Time Delays in Robotized Teleoperation.- Emerging Methodologies.- From Time Delay to Distributed Parameter Systems in Communications.- Computing Maximum Delay Deviation Allowed to Retain Stability in Systems with Two Delays.- On Exact Controllability of Linear Time Delay Systems of Neutral Type.- New Computational Methods.- Applied Interval Computation: A New Approach for Time-Delays Systems Analysis.- Mathematical and Computational Tools for the Stability Analysis of Time-Varying Delay Systems and Applications in Mechanical Engineering.- Diffusive Representation for Operators Involving Delays.- OreModules: A Symbolic Package for the Study of Multidimensional Linear Systems.- Predictors, Inversion and Filtering.- Inversion and Tracking Problems for Time Delay Linear Systems.- Finite Impulse Response Systems for Almost Perfect Decoupling in Nonminimum-Phase Plants.- Linearization of the Power Amplifier in Mobile Telecommunications.- Merging Saturations and Input Delays.- Robust Sampled-Data Control: An Input Delay Approach.- Stabilization and Finite-Gain Stabilizability of Delay Linear Systems Subject to Input Saturation.- Global Asymptotic Stabilization of a PVTOL Aircraft Model with Delay in the Input.

With the rapid development of vehicular sensor networks (VSNs) technology, the potential use of networked real-time control and automation is enormous and appealing. However, closed-loop control VSNs via the Internet are very difficult to implement practically because of their stochastic nature. One of the biggest challenges in VSNs is how to deal with sensor networks time delay and data loss. The authors investigate the potential of using the predictive control scheme for VSNs based on round-trip time (RTT) delay prediction to overcome the VSNs transmission delay and data loss. The predicted RTT delay is taken as the sampling interval reference for variable-period sampling approach. Modelling the time delay of networked control systems as a non-linear time series, the least mean square (LMS) filter algorithm is adopted to predict online the time delay induced in VSNs. The simulation results show that the LMS algorithm can achieve ideal efficacy if time delay has no variety abnormally. The predictive compensation strategy is proposed to reduce the detrimental effect of stochastic time delays induced by communication networks on control performance. The results of offline simulations via the Internet illustrate that the predictive control scheme based on RTT delay prediction has the potential to overcome the VSNs time delay and data loss.

This paper deals with time delays which exist in networked control systems due to presence of communication network. Time delay impact on networked control system stability is analyzed, and some relations for maximum allowable delay bound estimation are given as well. It is shown, on example of DC motor control, that the system behaves in desired manner and remains stable when appropriate values of regulator parameters are chosen to match estimated maximum time delay.

Time delay compensation is very important in the teleoperation field because time delay deteriorates the system performance and stability. Therefore, a lot of research about time delay compensation have been proposed and developed. One of the effective methods, communication disturbance observer (CDOB) has realized the time delay compensation for the position tracking in bilateral teleoperation. Thanks to CDOB, the smooth operation has been achieved. However, the precise force matching has not been achieved yet by any methods. To solve this problem, the time delay compensation method for the force control system has been proposed. This method realizes the precise contact force control under time delay. Therefore, the time delay compensation method is extended to bilateral teleoperation in this paper. In other words, the time delay compensation for the force controller in the bilateral teleoperation system is proposed toward the precise force matching. The validity is confirmed by the experiments.

In most of biomedical signal processing applications the presence of interference signals is inevitable. Processing of lung sounds is not an exemption. In this case the heart sounds are unavoidable and sometimes a severe disturbing noise source. Previous studies indicated that the performance of any interference cancellation scheme relies strongly on an adequate time delay estimation between the reference and the primary signals. Here, a new procedure for time delay estimation using the multi-resolution framework is presented. The proposed methodology possesses such key benefits as the multiple looks information of a signal at different bands, robustness in presence of noise and a validation procedure for the delay estimates. The procedure is applicable to a broad range of problems where time delay estimation is required. Results obtained with lung sounds show the promise of the scheme for the time delay estimation and subsequent interference cancellation.

The performance of a networked control system (NCS) is affected directly and indirectly by time delays generated in network communication. This paper addresses these time delays, their effects on system performance and the measures taken in an NCS design. For a time delay that is random but less than one sampling interval T, we model the system as a time-invariant control system with constant time delay T. For a time delay that is random and greater than one sampling interval T, we consider the system as a control system with packet drop and model it as a jump linear control system. Based on the above models, we propose a systematic method to improve the control system quality of performance by choosing a proper sampling interval to reduce data transmission, optimally scheduling to minimise packet loss and optimising controller design in case of packet loss. The simulation results and lab experiments demonstrate that the design method results in high performance in networked real-time control system.

Accurate localization in harsh indoor environments has long been a challenging problem due to the presence of multipath. Since joint direction-of-arrival (DOA) and time delay (TD) estimation has the capability to separate the line-of-sight signal from multipath signals in the TD space, it has recently become a key technique for accurate indoor localization in next-generation WiFi and 5G networks. This paper addresses the problem of joint azimuth, elevation, and TD estimation of multiple reflections of a known signal. First, we propose an efficient approximate maximum likelihood algorithm for this problem, which updates the DOA and TD parameters alternatingly. This algorithm applies to arbitrarily distributed (planar or 3-D) arrays. Then, we present the closed-form Cramer–Rao bound for joint DOA and TD estimation, based on which we provide further analysis to show the benefit of joint DOA and TD estimation over DOA-only estimation. Although the benefit of joint estimation has been empirically shown long ago, our analysis is the first theoretical proof of it. Finally, simulation results have been provided to demonstrate the theoretical finding and the effectiveness of the new algorithm. Matlab code for the new algorithm is available at https://github.com/FWen/JADE.git .

Markovian jumping systems have arisen naturally in the mathematical modeling of phenomena spanning disciplines in the social sciences, natural sciences, and engineering. This kind of stochastic dynamical systems can be employed to model the dynamics when parameters are subject to random abrupt changes due to sudden environment changes, subsystem switching, system noises, executor faults, and so forth. Much attention has been given to modeling, optimization, and real applications of such stochastic dynamical systems in the literature in recent years. As the advanced control and optimization will provide a basis for the design and application of such stochastic systems, these advanced techniques would result in substantial and sustainable benefits. The accepted papers in this special issue include stochastic stability, stabilization, stochastic control optimization, system modeling and identification methods, predictive control, signal processing, robust filtering, multiagent systems, networked control systems, time-delayed systems, neural networks, the Takagi-Sugeno fuzzy systems, simulated annealing, and fault detection methods.

In this paper, the time-delay compensation control of a class of networked control system (NCS) with randomly varying long time-delays is addressed. Firstly, we give a novel modeling method which is easy to implement time delay compensation. By prediction of a model-based estimator in the controller node and building buffers in the actuator node, the NCS with delayed state feedback is compensated. A linear matrix inequality based (LMI-based) sufficient condition for stability of the NCS with time-delay compensation is derived. The simulation results of an Internet-based continuous stirred tank reactor (CSTR) demonstrate the efficiency and correctness of our compensation method.

Based on the controlled process that is linear time-invariant system, the network-induced long time delay is viewed as time-varying parameter uncertainties. The uncertainty parameters model of networked control systems with long time delay is set up. The existing conditions of asymptotic stability for networked control system with long time delay are presented by Lyapunov method and robust control theory. The design method of stabilization controller for networked control system is proposed in terms of linear matrix inequalities. In the end the simulation based on the networked control unstable system is studied. The simulation results show the proposed controller is feasible and effective.

Control systems with digital communication between sensors, controllers and actuators are called Networked Control Systems (NCSs). In general, NCSs encounter with some problems such as packet dropouts and network induced delays. When plant uncertainty is added to the aforementioned problems, the design of the robust controller that is able to guarantee the stability becomes more complex. In this paper, a method based on Robust Model Predictive Control (RMPC) is proposed to overcome model uncertainty together with unknown delay caused in NCSs. The previous RMPC methods, called Normal RMPC, was proposed to compensate delay or model uncertainty, individually. Hereby, we propose a method, named Improved RMPC, to compensate the effects of delay and model uncertainty on NCSs, simultaneously. The proposed method is based on uncertainty polytope and LMIs (Linear Matrix Inequlities). Also, an experimental evaluation of time-delays in MODBUS networked control systems is proposed. The simulation results show the ability of the proposed method. For comparison, the Normal RMPC is applied as well. The results show that the Normal RMPC has an acceptable performance for time delay compensation, but its performance gets destroyed or even get unstable when the model uncertainty is also considered.

This paper introduces a new method for enhancing bandwidth conservation in networked control systems (NCSs) through the integration of the single model scheme (SMS) with event-triggered predictive control (ETPC). NCSs face significant challenges from network-induced imperfections, such as time delays and packet dropouts which can compromise system stability and performance. The existing ETPC schemes assume a known bound on the time delays and packet dropouts and send futuristic input commands based on that bound accounting for the worst-case scenario, which overloads the network creating further congestion through bandwidth consumption. The proposed SMS-ETPC scheme addresses these limitations by employing a model that predicts both time delays and packet dropouts using a semi-continuous hidden Markov model (SCHMM) enhanced with Dirac-delta functions to account for the discrete nature of packet dropouts. Additionally, by incorporating event-triggered mechanisms (ETMs) in both feedback and forward channels, the SMS-ETPC framework reduces unnecessary data transmissions, conserves bandwidth consumption and accounts for time delays and packet dropouts. Simulation results demonstrate the efficiency of the SMS-ETPC scheme due to its inherent advantage of conservation of bandwidth in NCSs.

Bilateral teleoperation systems have been widely applied for human operators to manipulate slave robots in accomplishing various tasks within remote environments. However, most teleoperation systems developed previously have heavily relied on continuous communication or a network with higher sampling rates. In this study, the authors propose novel control schemes to guarantee stability and tracking performance of bilateral teleoperation by considering an event-based transmission. Based on local output signals and the proposed triggering mechanisms, the master and slave robots transmit signals over a communication network only when the triggering conditions are satisfied. An event-triggered coordinating controller is presented to guarantee stability and position tracking for non-linear teleoperators. Input-to-state stability of the proposed teleoperation system with bounded external forces is studied with guaranteed static force reflection. Subsequently, a transformation-based framework is addressed with the event-triggered coordinating control to cope with bilateral teleoperation systems under time delays. The Zeno behaviour is demonstrated to be excluded in the proposed event-triggered teleoperation systems. Numerical examples and experiments are presented to discuss the efficacy of the proposed event-triggered teleoperation systems.

An online delay estimation algorithm is adopted for the adaptive Smith predictor in the networked control systems (NCS) design under the significant delay time. However, the Smith predictor is sensitive to parameter uncertainties within the system model and time delay. The quantitative feedback theory (QFT) controller is suitable to cope with parameter uncertainties of the Smith predictor in this paper; moreover, a template expressed in phase and gain for the QFT design has been constructed by considering the bounded variations with the time delay and the external loading. Therefore, the adaptive Smith predictor control scheme with QFT controller provides better tolerance to parameter uncertainties. Both simulation and experimental results on AC servo motor with both the hybrid controller area network (CAN) bus and the Ethernet network have proven the feasibility and improved performance of the proposed NCS.