—Human operators play a key role in the reliable operation of critical infrastructures. However, ... more —Human operators play a key role in the reliable operation of critical infrastructures. However, human operators may take actions, which can be far from optimum, because of stressful situations and other factors affecting their performance in time-sensitive and critical situations such as reacting to contingencies with significant monetary and social impact. In this paper, we present an analytic framework based on a Markov chain for modeling the dynamics of an infrastructure under contingencies, while capturing the effects of operators behavior quantified by the probability of human error under various circumstances. In particular, we have focused on the power grid infrastructure and cascading failures as contingencies. We particularly leveraged the observations and information obtained from interviews with power-system operators to develop our model and identify its parameters. In light of the proposed model, non-critical regions of power-system operating-characteristic settings with human factor considerations are characterized under which the power grid can be resilient against cascading failures.
—Human operators play a key role in the reliable operation of critical infrastructures. However, ... more —Human operators play a key role in the reliable operation of critical infrastructures. However, human operators may take actions that are far from optimum. This can be due to various factors affecting the operators' performance in time-sensitive and critical situations such as reacting to contingencies with significant monetary and social impacts. In this paper, an analytic framework is proposed based on Markov chains for modeling the dynamics of cascading failures in power grids. The model captures the effects of operators' behavior quantified by the probability of human error under various circumstances. In particular, the observations from historical data and information obtained from interviews with power-system operators are utilized to develop our model as well as identify its parameters. In light of the proposed model, the non-critical regions of power-system operating characteristics with human factor considerations are characterized under which the power grid is able to prevent large cascading failures.
This paper presents a general framework for optimal task reallocation in heterogeneous distribute... more This paper presents a general framework for optimal task reallocation in heterogeneous distributed-computing systems and offers a rigorous analytical model for the stochastic execution time of a workload. The model takes into account the heterogeneity and stochastic nature of the tasks' service and transfer times, servers' failure times, as well as an arbitrary task-reallocation policy. The stochastic service, transfer and failure times are assumed to have general, age-dependent (non-exponential) distributions, resulting in a tandem distributed queuing system with non-Markovian dynamics. Auxiliary age variables are introduced in the analysis to capture the memory associated with the non-Markovian stochastic times, thereby enabling a regenerative age-dependent analytical characterization of the statistics of the execution time of a workload. The model is utilized to devise task reallocation policies that optimize three metrics: the average execution time of a workload, the quality-of-service in executing a workload by a prescribed deadline and the reliability in executing a workload. Implications of the non-exponential event times on these metrics are also studied. Key results are verified experimentally on a distributed-computing testbed.
Current power grids suffer periodic disturbances that may trigger cascades of component failures,... more Current power grids suffer periodic disturbances that may trigger cascades of component failures, which, in turn, can result in blackouts of different scales. Understanding cascading failures and the ability to predict the risk of blackouts are therefore of great value in designing control and outage management systems for future smart grids. In this paper, a novel probabilistic approach is proposed
Modern power grids rely heavily on their control systems operating over communication networks to... more Modern power grids rely heavily on their control systems operating over communication networks to mitigate the effects of stresses in the grid. However, the cascading phenomenon and blackouts remain possible if the initial disturbances in the power grid are accompanied by other system vulnerabilities such as failures of the communication and control systems that transmit and implement critical control signals.
—Human operators play a key role in the reliable operation of critical infrastructures. However, ... more —Human operators play a key role in the reliable operation of critical infrastructures. However, human operators may take actions, which can be far from optimum, because of stressful situations and other factors affecting their performance in time-sensitive and critical situations such as reacting to contingencies with significant monetary and social impact. In this paper, we present an analytic framework based on a Markov chain for modeling the dynamics of an infrastructure under contingencies, while capturing the effects of operators behavior quantified by the probability of human error under various circumstances. In particular, we have focused on the power grid infrastructure and cascading failures as contingencies. We particularly leveraged the observations and information obtained from interviews with power-system operators to develop our model and identify its parameters. In light of the proposed model, non-critical regions of power-system operating-characteristic settings with human factor considerations are characterized under which the power grid can be resilient against cascading failures.
—Human operators play a key role in the reliable operation of critical infrastructures. However, ... more —Human operators play a key role in the reliable operation of critical infrastructures. However, human operators may take actions that are far from optimum. This can be due to various factors affecting the operators' performance in time-sensitive and critical situations such as reacting to contingencies with significant monetary and social impacts. In this paper, an analytic framework is proposed based on Markov chains for modeling the dynamics of cascading failures in power grids. The model captures the effects of operators' behavior quantified by the probability of human error under various circumstances. In particular, the observations from historical data and information obtained from interviews with power-system operators are utilized to develop our model as well as identify its parameters. In light of the proposed model, the non-critical regions of power-system operating characteristics with human factor considerations are characterized under which the power grid is able to prevent large cascading failures.
This paper presents a general framework for optimal task reallocation in heterogeneous distribute... more This paper presents a general framework for optimal task reallocation in heterogeneous distributed-computing systems and offers a rigorous analytical model for the stochastic execution time of a workload. The model takes into account the heterogeneity and stochastic nature of the tasks' service and transfer times, servers' failure times, as well as an arbitrary task-reallocation policy. The stochastic service, transfer and failure times are assumed to have general, age-dependent (non-exponential) distributions, resulting in a tandem distributed queuing system with non-Markovian dynamics. Auxiliary age variables are introduced in the analysis to capture the memory associated with the non-Markovian stochastic times, thereby enabling a regenerative age-dependent analytical characterization of the statistics of the execution time of a workload. The model is utilized to devise task reallocation policies that optimize three metrics: the average execution time of a workload, the quality-of-service in executing a workload by a prescribed deadline and the reliability in executing a workload. Implications of the non-exponential event times on these metrics are also studied. Key results are verified experimentally on a distributed-computing testbed.
Current power grids suffer periodic disturbances that may trigger cascades of component failures,... more Current power grids suffer periodic disturbances that may trigger cascades of component failures, which, in turn, can result in blackouts of different scales. Understanding cascading failures and the ability to predict the risk of blackouts are therefore of great value in designing control and outage management systems for future smart grids. In this paper, a novel probabilistic approach is proposed
Modern power grids rely heavily on their control systems operating over communication networks to... more Modern power grids rely heavily on their control systems operating over communication networks to mitigate the effects of stresses in the grid. However, the cascading phenomenon and blackouts remain possible if the initial disturbances in the power grid are accompanied by other system vulnerabilities such as failures of the communication and control systems that transmit and implement critical control signals.
Uploads
Papers by Zhuoyao Wang