Zhong-Hua Pang

Output Tracking Control for Networked Systems: A Model-Based Prediction Approach

This paper studies the problem of output tracking for networked control systems with network-induced delay, packet disorder, and packet dropout. The round-trip time (RTT) delay is redefined to describe these communication constraints in a unified way. By including the output tracking error as an additional state, the output tracking problem is converted into the stabilization problem of an augmented system. Based on the observer of the original state increment and the feedback of the output tracking error, a model-based networked predictive output tracking control (NPOTC) scheme is proposed to actively compensate for the random RTT delay. The closed-loop stability is proved to be independent of the RTT delay, and the separation principle for the design of the observer-based state feedback controller is still held in the NPOTC system. A two-stage controller design procedure is presented, which not only guarantees the stability of the closed-loop NPOTC system but also achieves the same output tracking performance as that of the local control system for time-varying reference signals. Both numerical simulations and practical experiments on an Internet-based servo motor system illustrate the effectiveness of the proposed method.

Data-Based Predictive Control for Networked Nonlinear Systems With Network-Induced Delay and Packet Dropout

This paper addresses the data-based networked control problem for a class of nonlinear systems. Network communication constraints, such as network-induced delay, packet disorder, and packet dropout in both the feedback and forward channels, are considered and further treated as the round-trip time (RTT) delay that is redefined. By using the packet-based transmission mechanism and the model-free adaptive control algorithm, a data-based networked predictive control method is proposed to actively compensate for the random RTT delay. The proposed method does not require any information on the plant model and depends only on the input and output data of the plant. A simple and explicit sufficient condition, which is related to the upper bound of the RTT delays, is derived for the stability of the closed-loop system. Additionally, a zero steady-state output tracking error can be achieved for a step reference input. The effectiveness of the proposed method is demonstrated via simulation and experimental results.

Two-Channel False Data Injection Attacks Against Output Tracking Control of Networked Systems

This paper addresses the design problem of false data injection (FDI) attacks against the output tracking control of networked systems, where the network-induced delays in the feedback and forward channels are considered. The main contributions of this paper are as follows. 1) To actively compensate for the two-channel network-induced delays, a Kalman filter-based networked predictive control scheme is designed for stochastic linear discrete-time systems. 2) From an attackers perspective, stealthy FDI attacks are proposed for both the feedback and forward channels so as to disrupt the stability of the resulting closed-loop system while avoiding the detection of a Kalman filter-based attack detector. 3) Both numerical simulations and practical experiments are carried out to show the effectiveness of the proposed method.

Secure Networked Control Systems under Denial of Service Attacks

Abstract This paper addresses the security issue of networked control systems (NCSs) under DoS attacks. According to the level of attacks, DoS attacks are classified into two types: weak attacks and strong attacks. A recursive networked predictive control (RNPC) method based on round-trip time delay is proposed to compensate for the adverse effects introduced by the weak DoS attacks as well as the network communication constraints, such as random delay, packet disorder and packet loss. A theoretical result using the switched system theory is also obtained for the closed-loop stability of the RNPC system. For the strong DoS attacks on the controller side, a multi-controller switching scheme is presented, in which each controller is designed based on the RNPC. The performance of the proposed strategies is demonstrated by practical experiments to control a DC motor speed through the Internet under DoS attacks.

Design and Performance Analysis of Incremental Networked Predictive Control Systems

This paper is concerned with the design and performance analysis of networked control systems with network-induced delay, packet disorder, and packet dropout. Based on the incremental form of the plant input-output model and an incremental error feedback control strategy, an incremental networked predictive control (INPC) scheme is proposed to actively compensate for the round-trip time delay resulting from the above communication constraints. The output tracking performance and closed-loop stability of the resulting INPC system are considered for two cases: 1) plant-model match case and 2) plant-model mismatch case. For the former case, the INPC system can achieve the same output tracking performance and closed-loop stability as those of the corresponding local control system. For the latter case, a sufficient condition for the stability of the closed-loop INPC system is derived using the switched system theory. Furthermore, for both cases, the INPC system can achieve a zero steady-state output tracking error for step commands. Finally, both numerical simulations and practical experiments on an Internet-based servo motor system illustrate the effectiveness of the proposed method.

Data-Driven Control With Input Design-Based Data Dropout Compensation for Networked Nonlinear Systems

This brief investigates the regulation problem for a class of networked nonlinear systems with measurement noise, where random data dropouts in both the feedback and forward channels are considered. To actively compensate for the two-channel data dropouts, a data-driven networked compensation control method is proposed, which consists of two aspects: 1) to calculate a control increment based on the measured output error in the controller and 2) to design a data dropout compensation strategy based on the latest control increment available in the actuator. The proposed method merely depends on the input and output data of the controlled plant, without using explicit or implicit information of its mathematical model. Moreover, only one control command needs to be transmitted in the forward channel at each time instant. A sufficient condition is derived to guarantee the closed-loop stability and output error convergence. Both numerical simulations and experimental tests are conducted to demonstrate the effectiveness of the proposed method.

False data injection attacks for a class of output tracking control systems

With the development of cyber-physical systems (CPSs), the security becomes an important and challenging problem. Attackers can launch various attacks to destroy the control system performance. In this paper, a class of linear discrete-time time-invariant control systems is considered, which is open-loop critically stable and only has one critical eigenvalue. By including the output tracking error as an additional state, a Kalman filter-based augmented state feedback control strategy is designed to solve its output tracking problem. Then a stealthy false data attack is injected into the measurement output, which can completely destroy the output tracking control systems without being detected. Simulation results on a numerical example show that the proposed false data injection attack is effective.

Model-based recursive networked predictive control

A recursive networked predictive control (RNPC) approach is proposed for networked control systems (NCSs), which mainly consists of two parts: a control prediction generator (CPG) and a network delay compensator (NDC). Based on a NARMA model, the CPG is applied to generate control predictions using the historical input-output data of the plant. The NDC is designed in the actuator to actively compensate for the network communication constraints such as network-induced delay, data packet disorder, accumulation and dropout. The RNPC is easy to be implemented in practice compared with previous results in that the recursive method is used to derive the future output predictions and control predictions, and the round-trip time delay is also used in the compensation scheme. Two RNPC systems are designed for a DC motor Internet-based control system, which are based on the nonlinear model and the simply linearized model, respectively. Practical experiments have been carried out to demonstrate the effectiveness of the proposed approach.

Networked Predictive Control Based on State-Space Model

This chapter is devoted to the networked control of multiple-input multiple-output linear systems, where random network-induced delays, packet disorders, and packet dropouts in the feedback and forward channels are considered. To compensate for these communication constraints, a networked predictive control method is presented based on a state-space model. A stability condition is derived for the resulting closed-loop networked system, which also shows that the separation principle of the observer-based controller design still holds. Simulation and experimental results are given to illustrate the effectiveness of the proposed method.

Secure Networked Predictive Control Under DoS Attacks

This chapter is concerned with DoS attacks in NCSs, which are classified as weak attacks and strong attacks. For an NCS under weak DoS attacks, a networked predictive control method is designed to actively compensate for original RTT delays induced by communication networks and additional RTT delays introduced by weak DoS attacks. For an NCS under strong DoS attacks against networked controllers or communication channels, a multi-controller switching strategy is presented based on a networked predictive control scheme, which can guarantee the closed-loop control performance even if the current controller fails to work or the communication between the controller and the plant is cut off. Practical experiments are conducted to illustrate the effectiveness of the proposed methods.