Fractional Differential Equations

Networked control systems (NCSs) have been one of the main research focuses in academia as well as in industry for many decades and have become a multidisciplinary area. With these growing research trends, it is important to consolidate the latest knowledge and information to keep up with the research needs. In this paper, the NCS and its different forms are introduced and discussed. The beginning of this paper discusses the history and evolution of NCSs. The next part of this paper focuses on different fields and research arenas such as networking technology, network delay, network resource allocation, scheduling, network security in real-time NCSs, integration of components on a network, fault tolerance, etc. A brief literature survey and possible future direction concerning each topic is included.

Networked Control System: Overview and Research Trends

Networked control systems (NCSs) have, in recent years, brought many innovative impacts to control systems. However, great challenges are also met due to the network-induced imperfections. Such network-induced imperfections are handled as various constraints, which should appropriately be considered in the analysis and design of NCSs. In this paper, the main methodologies suggested in the literature to cope with typical network-induced constraints, namely time delays, packet losses and disorder, time-varying transmission intervals, competition of multiple nodes accessing networks, and data quantization are surveyed; the constraints suggested in the literature on the first two types of constraints are updated in different categorizing ways; and those on the latter three types of constraints are extended.

Network-Induced Constraints in Networked Control Systems—A Survey

Microgrids consist of multiple parallel-connected distributed generation (DG) units with coordinated control strategies, which are able to operate in both grid-connected and islanded modes Microgrids are attracting considerable attention since they can alleviate the stress of main transmission systems, reduce feeder losses, and improve system power quality When the islanded microgrids are concerned, it is important to maintain system stability and achieve load power sharing among the multiple parallel-connected DG units However, the poor active and reactive power sharing problems due to the influence of impedance mismatch of the DG feeders and the different ratings of the DG units are inevitable when the conventional droop control scheme is adopted Therefore, the adaptive/improved droop control, network-based control methods, and cost-based droop schemes are compared and summarized in this paper for active power sharing Moreover, nonlinear and unbalanced loads could further affect the reactive power sharing when regulating the active power, and it is difficult to share the reactive power accurately only by using the enhanced virtual impedance method Therefore, the hierarchical control strategies are utilized as supplements of the conventional droop controls and virtual impedance methods The improved hierarchical control approaches such as the algorithms based on graph theory, multi-agent system, the gain scheduling method, and predictive control have been proposed to achieve proper reactive power sharing for islanded microgrids and eliminate the effect of the communication delays on hierarchical control Finally, the future research trends on islanded microgrids are also discussed in this paper

/pdf/review-of-active-and-reactive-power-sharing-strategies-in-15l30c1smy.pdf

Review of Active and Reactive Power Sharing Strategies in Hierarchical Controlled Microgrids

The anticipation of a large penetration of plug-in hybrid electric vehicles (PHEVs) into the market brings up many technical problems that need to be addressed. In the near future, a large number of PHEVs in our society will add a large-scale energy load to our power grids, as well as add substantial energy resources that can be utilized. An emerging issue is that a large number of PHEVs simultaneously connected to the grid may pose a huge threat to the overall power system quality and stability. In this paper, the authors propose an algorithm for optimally managing a large number of PHEVs (e.g., 3000) charging at a municipal parking station. The authors used the estimation of distribution algorithm (EDA) to intelligently allocate electrical energy to the PHEVs connected to the grid. A mathematical framework for the objective function (i.e., maximizing the average state-of-charge at the next time step) is also given. The authors considered real-world constraints such as energy price, remaining battery capacity, and remaining charging time. The authors also simulated the real-world parking deck scenarios according to the statistical analysis based on the transportation data. The authors characterized the performance of EDA using a Matlab simulation, and compared it with other optimization techniques.

Performance Evaluation of an EDA-Based Large-Scale Plug-In Hybrid Electric Vehicle Charging Algorithm

This brief addresses the optimal-stabilization problem for networked control systems (NCSs) with time delays and packet losses. The closed-loop NCS is modeled as a discrete-time switched system, and the stability conditions are derived in terms of linear matrix inequality. A controller design method with both system stability and control performance taken into account is proposed, and estimation of distribution algorithm is used to select the optimal stabilizing gain. The proposed method can be easily implemented to various applications, since it has simple structure and has no assumptions on time-delay and packet-loss models. Simulation and experimental results are given to demonstrate the effectiveness of the proposed approach.

Optimal Stabilizing Gain Selection for Networked Control Systems With Time Delays and Packet Losses

This paper presents a new controller design method for networked DC motor system in the presence of time delays and packet losses. The sufficient condition under which the closed-loop system is asymptotically stable and the necessary condition under which the networked DC motor has zero steady-state tracking error are derived. Based on the obtained conditions, an output tracking controller design method is proposed, where the estimation of distribution algorithm is used to optimize the control parameters to improve the system control performance. The proposed method can be easily applied to various applications, since it is simple and has no assumptions on time delay and packet loss models. Simulation and experimental results are given to demonstrate the effectiveness of the proposed approach.

EDA-Based Speed Control of a Networked DC Motor System With Time Delays and Packet Losses

This study studies the problem of synchronisation control for spacecraft formation via extended state observer approach over directed communication topology. The attitude kinematics and dynamics of spacecraft are described by Lagrangian formulations, and the decentralised controller is designed with time-varying external disturbances and unmeasurable velocity information. In particular, the estimation of disturbances obtained via extended state observer is used for the decentralised controller design. A novel Lyapunov function is proposed to show that both static regulation and dynamic synchronisation are realised. Finally, simulation results are given to demonstrate the effectiveness of the controllers proposed in this study.

https://ietresearch.onlinelibrary.wiley.com/doi/epdf/10.1049/iet-cta.2013.0988

Adaptive control for attitude synchronisation of spacecraft formation via extended state observer

This paper presents a new controller design method for networked control systems (NCSs), which is motivated by that static state feedback control (SSFC) shows an offset in the plant output when there is nonzero disturbance. Different from the existing SSFC results, the proposed method constructs a gain-scheduling-based state feedback integral controller, where an integral action is introduced to address the nonzero disturbance issue, and most especially, a gain scheduling strategy is employed to improve the control performance of NCSs. Moreover, the obtained results are also extended to the output feedback case. Simulation and experimental results are given to demonstrate the effectiveness of the proposed approach.

Gain-Scheduling-Based State Feedback Integral Control for Networked Control Systems

This paper addresses the output feedback stabilization problem for a class of networked control systems (NCSs) under a multiple-packet transmission policy. To compensate the time delays and packet losses, a sliding-mode predictive controller is constructed by taking full advantage of network transmission capacity. A Kalman predictor is used to estimate the current and predict the future plant states, while sliding-mode control (SMC) is employed to compute the control sequences. The estimated state errors are transformed into a system disturbance, and the stability of the closed-loop NCSs is guaranteed by constructing the robust stabilizing SMC controller. Simulation and experimental results are given to demonstrate the effectiveness of the proposed approach.

Hongbo Li

Papers

Optimal Stabilizing Gain Selection for Networked Control Systems With Time Delays and Packet Losses

EDA-Based Speed Control of a Networked DC Motor System With Time Delays and Packet Losses

Adaptive control for attitude synchronisation of spacecraft formation via extended state observer

Gain-Scheduling-Based State Feedback Integral Control for Networked Control Systems

Sliding-Mode Predictive Control of Networked Control Systems Under a Multiple-Packet Transmission Policy