Resilient Distributed Control Research Articles

Resilient distributed secondary control for islanded AC microgrids under FDI attacks

For islanded AC microgrids under bounded and time-varying false data injection (FDI) attacks on actuators and communication links, a resilient distributed secondary control strategy is proposed to stabilize frequency and voltage at the reference values, and to achieve the optimal active power sharing. To mitigate the impact of FDI attacks on the stability of the islanded microgrid, extended-state observers are introduced to estimate the impact. Compared with the currently presented resilient distributed control strategies, which ensure the bounded stability of microgrids, the control objective that the synchronization of every distributed generator’s voltage and frequency to the reference values and the achievement of the optimal active power sharing is maintained by the proposed resilient control strategy. An example of an islanded AC microgrid is given to verify the proposed method.

Resilient distributed control of islanded microgrids under hybrid attacks

In this paper, a resilient control strategy is proposed to improve the stability of frequency and voltage recovery for the islanded microgrid (MG) under hybrid cyber attacks. To deal with the common false data injection attacks (FDI) and denial of service attacks (DoS) in MGs, the proposed resilient control strategy utilizes the observers to accurately estimate the potential FDI signals on both the sensors and actuators of each distributed generation unit (DG) and reconstruct the unavailable states in the system to enhance the system’s ability actively. The ultimate uniform boundedness (UUB) of the system under hybrid cyber attacks is proved by the Lyapunov stability theory. Finally, an islanded MG system is established in MATLAB/SIMULINK, and multiple scenarios are simulated to verify the effectiveness of the method.

Resilient distributed control of islanded microgrids under false data injection attacks

This paper concerns the frequency and voltage restoration problem of islanded microgrids under false data injection attacks. A resilient distributed frequency and voltage control protocol is proposed to mitigate bounded false data injection attacks, where an interaction network framework between the original communication network and the hidden network is developed. By using graph theory and a Lyapunov direct method, it is proved that the frequency and voltage of distributed generators can converge to a bounded and acceptable range whether the attacks occur on only the original communication network or both the original communication network and the hidden network. An islanded microgrid system is established in MATLAB/SIMULINK, and several scenario simulations are performed to verify the effectiveness of the proposed method.

The Synchronization of Networked Harmonic Oscillators Under Denial-of-Service Attacks

This article is concerned with resilient control design for synchronization of multiple harmonic oscillators coupled via vulnerable network suffering from denial-of-service (DoS) attacks. The synchronization of multiple harmonic oscillators can be achieved under consideration of certain DoS attacks. A distinct resilient distributed control protocol is designed for individual harmonic oscillator by proposing a resilient logical packet processor (RLPP). Some sufficient conditions on the duration and frequency of attacks reflected by the bounds of lumped time-varying delay are derived by employing complete-type Lyapunov–Krasovskii functionals (LKFs). The gain matrix can be designed by solving a set of linear matrix inequalities by combining an optimization algorithm. Finally, the proposed synchronization control scheme is applied to a representative model of the single-phase photovoltaic grid interconnection process. Numerical simulations are provided to show the effectiveness of the developed method.

Resilient time‐varying output formation tracking of heterogeneous linear multiagent systems under malicious false data injection attacks and denial‐of‐service attacks over digraphs

AbstractA distributed control fashion of cooperative formation tracking may be vulnerable to malicious attacks on sensors and communications that deteriorate the formation tracking performance or even destabilize the entire multiagent system. This article addresses a resilient time‐varying output formation tracking problem of linear heterogeneous multiagent systems, where an attacker can adversely inject false data injection (FDI) attacks on sensors and Denial‐of‐Service (DoS) attacks on communications. Both characteristics will not only enhance the practical relevance of the studied issue, but also bring nontrivial design challenges of distributed control algorithms and convergence analysis. A novel resilient distributed control architecture is developed to guarantee a global exponential time‐varying output formation tracking. In particular, the design includes features: (1) a resilient distributed leader estimator is developed to estimate the leader's state for each follower under DoS attacks over digraphs; (2) a distributed output feedback controller integrated with an observer‐based resilient mechanism is developed to achieve the time‐varying output formation tracking under attacks; (3) unlike existing related works to handle attacks as bounded disturbances or faults, the proposed design is resilient to enable exponential convergence, whereas many related works obtain uniformly ultimately boundedness (UUB) convergence. Simulation results are presented to validate the design's effectiveness.

Resilient Distributed Control Against Destabilization Attacks in DC Microgrids

The distributed control provides a flexible and scalable solution to coordinate voltages and currents in DC microgrids but introduces intrusion risk into the system. Destabilization attacks can manipulate system states by modifying the transferred data, which threatens the stable operation of DC microgrids. In this paper, a resilient distributed control consisting of an integrated distributed control and an additional state limitation strategy is proposed to cope with destabilization attacks. The current-sharing regulation is integrated into the average voltage regulation in the integrated distributed control. A steady-state analysis is conducted to verify the superior performance of the integrated distributed control against destabilization attacks. As a supplement, state limitation strategies aim to actively restrict magnitudes of system states. Inspired by results in the attack analysis, virtual attacks are constructed to limit the voltages and currents within tolerant ranges. Several cases, including the simulation and the experiment, are conducted to demonstrate the effectiveness of the proposed resilient distributed control.

A Resilient Distributed Control and Energy Management Approach for DERs and EVs with Application to EV Charging Stations

The rapid growth of Electric Vehicles (EVs) and their charging infrastructure has given rise to various challenges regarding the stable operation of EV charging stations (CSs). Vehicle-to-Vehicle (V2V) charging schemes decrease the dependency on CSs, but they also increase the reliance on a single source type. This maximizes the charging cost and minimizes the system continuity rate. In this work, energy routing-based resilient distributed control is presented by emphasizing the flexibility of Distributed Energy Resources (DERs). This provides an efficient energy management framework for EV CSs with optimal power sharing and cost-effective energy trading, by enabling DERs to EVs and V2V energy transactions. The dynamic performance of the proposed scheme is enhanced by using the Augmented Lagrangian approach. The resiliency of this distributed control approach is quantified by using a resiliency matrix to reflect its enhanced continuity under different system disturbances. The effectiveness of the proposed model is validated by considering different case study scenarios of EV-loading and system-level disturbances.

Resilient Control for Multiagent Systems With a Sampled-Data Model Against DoS Attacks

To reduce the computational burden and resist the denial-of-service (DoS) attacks, a resilient distributed sampled-data control scheme is proposed for multiagent systems. The agent states are sampled periodically by the sensors. DoS attacks disrupt the data communication from transmitters to controllers randomly or periodically with a limited duration time. Information on DoS attacks can be obtained by introducing novel logic processors embedded in corresponding controllers. Next, the problem of resilient control can be converted into one concerned with the upper and lower bound of the sampling interval of an aperiodic sampled-data control system. Some sufficient criteria for developing resilient distributed controllers are derived using the novel looped Lyapunov functional approach and the free-matrix-based inequality method. Finally, two illustrative examples, unmanned aerial vehicles and the two-mass-spring systems, are provided to demonstrate the efficiency of the proposed resilient distributed sampled-data control protocols against the DoS attacks.

A novel resilient state of charge balancing method for distributed storage systems based autonomous microgrids

In order to reduce the number of charge/discharge cycles of distributed energy storage systems (DESSs) to extend their lifespan, a State-of-Charge (SoC) balancing control is used. In conventional SoC balancing strategies, a local integral control is generally introduced in each DESS to ensure SoC equalization and Distributed Generators (DGs) frequency restoration. These strategies increase the system order and have a constraining bandwidth that may lead to stability issues. The few methods in which a local integrator is not added generally result in poor performance of the SoC synchronization strategy and frequency restoration, with the inability to eliminate static error. In this proposal, a novel resilient distributed control is proposed to ensure an effective SoC balancing of DESSs and frequency restoration with high performance without increasing the system order with a local integral control. The dynamic average consensus is modified to evaluate the participation level of each DESS in order to determine the active power references to synchronize the SoCs of the DESSs. These active power references are chosen to regulate the DG frequency to the nominal frequency of the MG. Therefore, the proposed method ensures SoC balancing with automatic frequency regulation and accurate output power sharing performance. Only voltage restoration control is added for DGs voltage regulation. In this distributed control architecture, SoC equalization as well as voltage/frequency restoration are performed only with local DG information and information from their neighbors. Simulations and then experimental results are performed to verify the effectiveness of the proposed method in discharging mode, in charging mode, in the presence of intermittent renewable energy sources, in the case of communication failure, in the case of communication delay, in the case of load variation, and in the case of “plug and play”. Comparisons were also made with two SoC balancing strategies from the literature.

Resilient average consensus on general directed graphs in presence of cyber-attacks

This paper proposes a resilient distributed control scheme that ensures average consensus in multi-agent systems with continuous-time single-integrator kinematics in the presence of cyber-attacks. Potential cyber-attacks considered on such systems are in the form of unknown uniformly bounded false data injection (FDI) to control input channels (actuators) and also eavesdropping attacks. The purpose of such cyber-attacks is to disturb the average consensus in multi-agent systems and also to disclose the states of agents. The proposed resilient distributed average consensus protocol includes a set of virtual variables/states being exchanged via a communication network given by a general directed graph (digraph) and is designed to make the closed-loop system stable and preserve the average consensus regardless of the existence of cyber-attacks. Unlike the existing literature, the proposed distributed average consensus framework does not require any conditions on directed graphs to be strongly connected, balanced, or symmetric. A graph-theoretical approach, Lyapunov direct method, and LaSalle’s invariance principle are used to guarantee the rigorous stability of multi-agent systems augmented with the proposed distributed algorithm. Simulation results validate the theoretical contributions of this paper.

A Fully Resilient Cyber-Secure Synchronization Strategy for AC Microgrids

This letter focuses on resilient synchronization in networked ac microgrids under cyber-attacks, where attackers aim to desynchronize converters by injecting bounded false data to communication and control channels. To this end, a resilient cooperative control framework for the secondary frequency regulation in ac microgrids is developed. The proposed resilient distributed control strategy achieves synchronization regardless of the existence of cyber-attacks. Moreover, it offers the maximum level of resilience, i.e., it guarantees resilient synchronization even if all distributed generation units in microgrids are subject to cyber-attacks. Theoretical analysis and verification case studies are carried out in order to demonstrate the advantages and performance of the proposed resilient cooperative control.

Distributed resilient control against denial of service attacks in DC microgrids with constant power load

Recent events have shown that cyber attacks are becoming real threats to the power system reliability and resiliency, and there is no exception to the DC microgrids which would become popular in the future. Currently, most secondary controls in DC microgrids heavily rely on communications, making them specifically vulnerable to cyber attacks. This paper presents a resilient distributed control based on the average consensus algorithm and the proportional-integral (PI) consensus algorithm to enhance the system resilience against denial of service attacks and improve the microgrid stability, particularly in the presence of constant power loads. The proposed control casts the average voltage restoration problem into an optimization problem, and because of this, the voltage control is immune to the communication damage caused by malicious denial of service attacks. Moreover, the small-signal stability model of the DC microgrid with distributed energy storages and constant power loads is established, and the impacts of varying constant power loads, controller parameters and communication topology on the system stability are analyzed. Simulations are conducted to verify the effectiveness of the proposed method.

A resilient control strategy for networked multi-agent systems subject to covert attacks

In this paper, a resilient distributed control scheme against covert attacks for multi-agent networked systems subject to input and state constraints is developed. The idea consists in a clever deployment of predictive arguments with a twofold aim: detection of malicious agent behaviors affecting the normal system operations and consequent specific control actions implementation to mitigate as much as possible undesirable knock-on effects resulting from adversary actions. Specifically, the multi-agent system is organized in terms of a grid topology and set-theoretic receding horizon control ideas are exploited to develop a distributed algorithm capable to recognize the attacked agent. In essence, the resulting solution relies on the combined use of predictive control and set-invariance ideas that are exploited to generate redundant control sequences randomly selected on the actuator side such that the malicious agent is never aware about the effective control action indeed exploited. As a consequence, countermeasures on the sensor-to-controller channel could lead to significantly erroneous data not complying with the expected evolution of the system modeling. Finally, numerical simulations are carried out to show benefits and effectiveness of the proposed approach.

Observer-Based Resilient Integrated Distributed Control Against Cyberattacks on Sensors and Actuators in Islanded AC Microgrids

Compared with centralized control, distributed control for microgrids offers higher reliability and scalability. However, distributed control faces severe problems for maintaining the microgrid cybersecurity, which is due to the absence of central controllers for monitoring participating generation unit activities. This article proposes an observer-based resilient distributed control for AC microgrids that estimates and compensates false data injection (FDI) attacks on sensors and actuators. The proposed resilient control relies on an integrated distributed control structure, which restores the rated frequency/voltage and offers the proportional active/reactive power sharing with reduced exchanges of control signals. The proposed control has no limitation on the number of disrupted DGs and does not need access to the attack information. The H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> ∞</sub> output feedback control is applied to guarantee the L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -gain boundedness of the control system. Several case studies are presented to verify the effectiveness of the proposed resilient distributed control in the PSCAD/EMTDC platform.

Stability Oriented Design of Cyber Attack Resilient Controllers for Cooperative DC Microgrids

Due to the importance of reliability and security in dc microgrids, it is essential to provide maximum resilience against cyberattacks. However, insufficient global information in the microgrid makes it difficult to accurately identify the location of these attacks. To address these issues, this article develops a novel resilient distributed control mechanism, which ensures average voltage regulation and proportional load sharing in dc microgrids under unknown cyberattacks. The proposed resilient control design does not require any information regarding the nature or location of the attacks. By virtue of a graph theoretical approach and a Lyapunov-based framework, the proposed resilient distributed control strategy is designed in a way such that the system stability is always guaranteed following a comprehensive design mechanism. Finally, the robustness of the proposed resilient distributed control approach is demonstrated via simulations and validated by experimental results.

Resilience Against Replay Attacks: A Distributed Model Predictive Control Scheme for Networked Multi-Agent Systems

In this paper, a resilient distributed control scheme against replay attacks for multi-agent networked systems subject to input and state constraints is proposed. The methodological starting point relies on a smart use of predictive arguments with a twofold aim: 1) Promptly detect malicious agent behaviors affecting normal system operations; 2) Apply specific control actions, based on predictive ideas, for mitigating as much as possible undesirable domino effects resulting from adversary operations. Specifically, the multi-agent system is topologically described by a leader-follower digraph characterized by a unique leader and set-theoretic receding horizon control ideas are exploited to develop a distributed algorithm capable to instantaneously recognize the attacked agent. Finally, numerical simulations are carried out to show benefits and effectiveness of the proposed approach.

Active and Reactive Power Control of PEV Fast Charging Stations Using a Consecutive Horizon-Based Energy Management Process

The energy management of the fast-charging stations (FCSs) in power systems, while maintaining the power quality and the grid codes, can be particularly challenging, given the highly dynamic load curve, the heterogeneous PEV charging, and the inconvenience to the FCS customers. In this article, a consecutive horizon-based energy management (CHEM) process is proposed for the optimal techno-economic operation of the FCSs integrated with battery energy storage systems (ESS). The proposed CHEM process employs a central supervisory control and a resilient distributed control, for the energy management of FCSs and the active and reactive power control to maintain the grid codes. As such, the grid operator can realize and direct the economic and technical operation of the FCSs with low computational burden, without the need for real-time collaboration with the FCSs. Moreover, the FCSs can autonomously cope with the volatility of PEV charging with the use of the ESS. Furthermore, a novel Volt/VAr control is proposed to confine the unpredicted voltage deviations, including voltage sags, within an acceptable limit. The heterogeneous PEV charging is modeled using the queuing theory, while the inherent characteristics of the lithium-ion batteries are considered. Through multiple case studies, it is shown that the developed CHEM process can provide lower costs and a leveled active power profile for the FCSs, while ensuring that the voltage deviations are well confined and the convenience of PEV owners can still be met.

Resilient distributed control of BESSs and voltage source converter‐based microgrids considering switching topologies and non‐uniform time‐varying delays

In this study, a distributed resilient control (DRC) scheme is proposed for inverter-interfaced autonomous AC microgrids (MGs). Due to unavoidable telecommunication vulnerabilities, time-delays already exist in communication links, and it seriously impresses the stability and performance of the network. Due to this fact, non-uniform time-varying communication delays are considered on the communication links (here, information exchanges between neighboring local controllers of DGs and BESSs). The authors consider a time-varying topology for distributed energy resources to address the uncertainties of communications links, improve flexibility, and enhance the security of the system against cyber-attacks. Stability analysis is characterised based on the Lyapunov–Krasovskii theory, and sufficient conditions for a precise and comprehensive control algorithm are derived in terms of linear matrix inequalities (LMIs). The provided LMIs yield the upper bound of the time delay, which guarantees the stability of the system. Finally, to evaluate the performance of the control law, offline digital time-domain simulation studies are performed on a test MG system in a MATLAB/Simulink environment, and also the results are compared with previously reported methods.

Steady-State Analysis of Microgrid Distributed Control Under Denial of Service Attacks

Distributed control is an effective method to coordinate multiple components in a microgrid. It usually has mandatory requirements for communication graph topology; changing the topology unexpectedly could disrupt the operation of a distributed controller. A denial of service (DoS) attack blocks communication channels to cause variations in communication graph. Unforeseen topology changes render a controller to receive incomplete system information. Control decisions made based on incorrect information can lead to significantly reduced grid supporting capability. As a result, the vital power balance between generation and load may be challenged. Determining power balance requires steady-state power flow analysis; however, the cyber-induced steady-state analysis is not well studied in the literature. In this article, we show that a cyber–physical microgrid with unknown DoS attacks has augmented uncertain power flow equations, whose special structure creates new computational issue to determining power balance. To deal with the issue, we develop a novel cyber-induced microgrid model: the cyber–physical system is transformed into a pure physical model, where the disruption effects of DoS in the cyber layer are shown to be equivalent to the variations of the physical model parameters. With the transformed system, we develop a sufficient condition to ascertain the system power balance under unknown DoS attacks. In addition, practical insights for resilient distributed control design are shown as well.

Resilient cooperative control of AC microgrids considering relative state‐dependent noises and communication time‐delays

In this study, a resilient distributed control algorithm is proposed for the secondary voltage and frequency restoration of an autonomous inverter-based microgrid considering simultaneous relative state-dependent noises and communication time-delays (CTDs). The proposed algorithm is robust against potential time-varying stochastic noises and CTDs, which corrupt the data exchanges in the secondary control layer. Additionally, this study considers the contribution of both distributed generation and distributed energy storage (DES) units in islanded AC microgrids. The presence of DES creates the need for an extra control algorithm to provide state-of-charge (SoC) balancing for these units and having precise active power-sharing. The theoretical concepts of the proposed control algorithm, including the mathematical modelling of microgrid, basic lemma, and controller design procedure, are outlined. The performance assessment of the presented control algorithm is evaluated through simulations on a test microgrid in MATLAB/Simulink software. Then, some previously-reported algorithms are selected to compare the proposed control algorithm with them. The obtained results show the effectiveness and robustness of the presented algorithm in regulating the voltage and frequency, matching SoCs, and as a result, having precise active power-sharing.