Yingmeng Xiang

A Robustness-Oriented Power Grid Operation Strategy Considering Attacks

Power system operation is facing increasing cyber and physical attack risks, so it becomes pressing to develop effective methods to improve the robustness of electric power infrastructure in the presence of significant attacks. As it is not guaranteed that attacks can always be detected and thwarted before they cause disturbances and damages to the power systems, increased robustness can contribute to reducing the consequence of attacks. In this paper, a holistic robustness framework is proposed by extending the conventional security-constrained optimal power flow (SCOPF) analysis to incorporate the risk caused by attacks. The corresponding solution methodology is proposed by combining particle swarm optimization and primal-dual interior point methods. Case studies conducted based on several test systems demonstrate that the proposed SCOPF model is able to reduce the consequence of attacks. This paper can provide some insight into improving the power system operation robustness in the face of significant attacks.

Coordinated attacks against power grids: Load redistribution attack coordinating with generator and line attacks

With the increasing terrorism and sabotage activities, the power grid is becoming more vulnerable to various kinds of cyber and physical attacks. The coordination between the attacks could bring disastrous impacts. In this paper, two typical attack coordination scenarios are studied: the coordination between load redistribution (LR) attack and generator attack; and the coordination between LR attack and line attack. They are formulated as bilevel optimization problems, where the attacker in the upper level aims to maximize the load curtailment while the defender in the lower level makes effort to reduce the load curtailment. The case studies conducted based on an IEEE 14-bus system indicate that when attacking the measurements and essential generation/transmission elements in a coordinated manner, the attacker could maximize the damage with the limited attack resource by disrupting the physical system and misleading the power dispatch simultaneously. This study can provide meaningful insights on how to prevent and mitigate such high-impact, low-frequency (HILF) coordinated attacks.

A game-theoretic approach to optimal defense strategy against load redistribution attack

The wider deployment of advanced computer and communication technologies in the cyber monitoring and control layer of power system will inevitably make the power grid more vulnerable to various cyber attacks, such as false data injection attack and load redistribution (LR) attack. It is critical to develop methods to study the interaction between the attacker and defender for finding the optimal allocation of the limited defense resources. In this study, the LR attack considering the attack and defense is modeled by bilevel optimization. Game-theoretic approaches are developed to model the interaction of the attacker and defender for two scenarios for defending critical measurements and for defending critical substations. The attack and defense interaction is modeled by a zero-sum game if only the load curtailment is considered in the utility functions. And it can be modeled by a non-zero-sum game if both the load curtailment and the associated attack cost and defense cost are considered. The proposed approach is tested based on a representative IEEE 14-bus system, and optimal defense strategies are derived in different scenarios. This study can offer some meaningful insight on effectively preventing and mitigating the LR attack.

Quantifying the influence of local load redistribution attack on power supply adequacy

With the broader deployment of cyber technologies in electric power systems, the envisioned cyber-physical smart grid will be more vulnerable to malicious cyber attacks including local load redistribution (LR) attack which can affect the outcome of state estimation. It is crucial to evaluate the potential impact of local LR attacks on the power system adequacy in a long time span for the next-generation power grid. In this study, the local LR attack is mathematically modeled as a bilevel optimization problem. The long-term occurrence frequency of local LR attacks is represented by the power law distribution. Considering the difficulty and consequence of each attack region, probability of choosing the valid attack region is calculated. A holistic framework for incorporating the local LR attack into the conventional power system adequacy assessment is proposed. Simulations are conducted based on a modified IEEE 14-bus system. Simulation results demonstrated that the impact of local LR attacks on power system adequacy should not be neglected if such attacks occur frequently in the future.

Bulk power system reliability evaluation considering optimal transmission switching and dynamic line thermal rating

Power system operators are faced with the increasingly complicated operating condition of bulk power systems. Due to the huge investment needed to build new power delivery facilities, cost-effective solutions such as new operational strategies are becoming more attractive in the recent years. Optimal transmission switching (OTS) and dynamic thermal rating (DTR) are such cost-effective technologies which offer a potential solution to improving the power system reliability by more fully utilizing the existing power delivery assets. In this paper, these two technologies are discussed, which are then incorporated into the reliability evaluation procedure for the power system. Case studies are conducted on a modified RTS-79 system using MATLAB and CPLEX. The obtained simulation results show that with the enforcement of either OTS or DTR, the overall system reliability can be improved, and system reliability can be further improved if both technologies are enforced.

Impact of network topology optimization on power system reliability

Due to the increasing power demand and the aging equipment, the electric power grid is faced with pressing challenges for maintaining its power supply reliability in an efficient and economical manner. Network topology optimization (NTO) is a promising, cost-effective method to improve the operational flexibility and the overall reliability of power systems. In this study, NTO is incorporated into the conventional reliability evaluation framework, and case studies are conducted based on a representative reliability test system. The simulation results demonstrate that the overall power system reliability could be improved assuming NTO is incorporated into the power system operation procedure. This study could offer some insights into improving power supply reliability by more fully utilizing the existing assets in a power system.

Critical line identification for hypothesized multiple line attacks against power systems

Growing vandalism and terrorist activities pose great challenges to securing the modern power grid. As a practical high-impact, low-frequency threat, the attackers could simultaneously sabotage multiple critical transmission lines in a coordinated manner to initiate the cascading failure for causing great blackout. Thus, it is pressing to study the hypothesized multiple line attack strategies. In this study, the static strategy, dynamic strategy and space-pruning searching strategy are proposed for more effectively identifying the critical lines in the multiple line attack scenarios. And the optimal selection of critical lines in the multiple lines attack is determined based on the criticality of the lines, which is modeled by several mathematical indices developed from graph theory or based on enumeration. The effectiveness of the proposed attack strategies is tested using three bulk IEEE test systems. This study provides some meaningful insights about malicious attacks targeting the critical transmission lines.

Identification of critical line-generation combinations for hypothesized joint line-generation attacks

The increasing load demand is pushing power system to operate near its limit, making it more vulnerable to various disturbances and attacks, especially those that might initiate cascading failures. In this study, the joint line-generation attack is introduced which assumes that the lines and generators can be tripped by malicious attacks simultaneously, and it is a natural extension of the previous node-only or line-only attacks. The joint line-generation attack strategy is explored based on a search space reduction algorithm. The simulation is conducted based on several representative test systems. The performance of the proposed attack strategy is compared with other attack strategies and the computational burden is analyzed. It is demonstrated that the proposed attack strategy is effective and computationally efficient. This work can provide some meaningful insight on how to prevent power system cascading failures initiated by joint attacks.

A resilient power system operation strategy considering presumed attacks

Power system operation is facing increasing cyber and physical attack risks and it is pressing to develop effective methods to improve the resiliency of electric power infrastructure against malicious attacks. In this study, a holistic resiliency framework is proposed by extending the conventional security-constrained optimal power flow analysis (SCOPF) to incorporate the presumed risk caused by the attacks. The improved solution method is studied by combining particle swarm optimization, primal-dual interior point (PDIP) method and parallel computing. The case studies conducted on IEEE 39-bus and 118-bus systems demonstrate the proposed SCOPF model is able to improve the resiliency of power system for the presumed attacks. This study can provide some meaningful insights on improving the power system operation resiliency.

Reliability evaluation of active distribution systems considering energy storage and real-time electricity pricing

Due to the increasing integration of renewable resources and the deployment of energy storage units at the power distribution level, conventional deterministic approaches may not be suitable or effective for evaluating the reliability of active distribution networks anymore. This paper proposes a new method to evaluate the active distribution system reliability including microgrid and energy storage. The power output of distributed generator (DG) within the microgrid is first calculated based on the approach of generalized capacity outage tables (GCOTs). Then Monte Carlo Simulation (MCS) is utilized for performing power system reliability evaluation. The results obtained considering different energy storage capacities are compared. Furthermore, real-time pricing (RTP) strategy is considered in optimizing the control strategy of the energy storage device and the corresponding reliability indices are recalculated.