2,221 research outputs found
Network hierarchy evolution and system vulnerability in power grids
(c) 2016 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other users, including reprinting/ republishing this material for advertising or promotional purposes, creating new collective works for resale or redistribution to servers or lists, or reuse of any copyrighted components of this work in other works.The seldom addressed network hierarchy property and its relationship with vulnerability analysis for power transmission grids from a complex-systems point of view are given in this paper. We analyze and compare the evolution of network hierarchy for the dynamic vulnerability evaluation of four different power transmission grids of real cases. Several meaningful results suggest that the vulnerability of power grids can be assessed by means of a network hierarchy evolution analysis. First, the network hierarchy evolution may be used as a novel measurement to quantify the robustness of power grids. Second, an antipyramidal structure appears in the most robust network when quantifying cascading failures by the proposed hierarchy metric. Furthermore, the analysis results are also validated and proved by empirical reliability data. We show that our proposed hierarchy evolution analysis methodology could be used to assess the vulnerability of power grids or even other networks from a complex-systems point of view.Peer ReviewedPostprint (author's final draft
Mitigating Cascading Failures in Interdependent Power Grids and Communication Networks
In this paper, we study the interdependency between the power grid and the
communication network used to control the grid. A communication node depends on
the power grid in order to receive power for operation, and a power node
depends on the communication network in order to receive control signals for
safe operation. We demonstrate that these dependencies can lead to cascading
failures, and it is essential to consider the power flow equations for studying
the behavior of such interdependent networks. We propose a two-phase control
policy to mitigate the cascade of failures. In the first phase, our control
policy finds the non-avoidable failures that occur due to physical
disconnection. In the second phase, our algorithm redistributes the power so
that all the connected communication nodes have enough power for operation and
no power lines overload. We perform a sensitivity analysis to evaluate the
performance of our control policy, and show that our control policy achieves
close to optimal yield for many scenarios. This analysis can help design robust
interdependent grids and associated control policies.Comment: 6 pages, 9 figures, submitte
Nonlocal failures in complex supply networks by single link additions
How do local topological changes affect the global operation and stability of
complex supply networks? Studying supply networks on various levels of
abstraction, we demonstrate that and how adding new links may not only promote
but also degrade stable operation of a network. Intriguingly, the resulting
overloads may emerge remotely from where such a link is added, thus resulting
in nonlocal failure. We link this counter-intuitive phenomenon to Braess'
paradox originally discovered in traffic networks. We use elementary network
topologies to explain its underlying mechanism for different types of supply
networks and find that it generically occurs across these systems. As an
important consequence, upgrading supply networks such as communication
networks, biological supply networks or power grids requires particular care
because even adding only single connections may destabilize normal network
operation and induce disturbances remotely from the location of structural
change and even global cascades of failures.Comment: 12 pages, 10 figure
Stochastic Model for Power Grid Dynamics
We introduce a stochastic model that describes the quasi-static dynamics of
an electric transmission network under perturbations introduced by random load
fluctuations, random removing of system components from service, random repair
times for the failed components, and random response times to implement optimal
system corrections for removing line overloads in a damaged or stressed
transmission network. We use a linear approximation to the network flow
equations and apply linear programming techniques that optimize the dispatching
of generators and loads in order to eliminate the network overloads associated
with a damaged system. We also provide a simple model for the operator's
response to various contingency events that is not always optimal due to either
failure of the state estimation system or due to the incorrect subjective
assessment of the severity associated with these events. This further allows us
to use a game theoretic framework for casting the optimization of the
operator's response into the choice of the optimal strategy which minimizes the
operating cost. We use a simple strategy space which is the degree of tolerance
to line overloads and which is an automatic control (optimization) parameter
that can be adjusted to trade off automatic load shed without propagating
cascades versus reduced load shed and an increased risk of propagating
cascades. The tolerance parameter is chosen to describes a smooth transition
from a risk averse to a risk taken strategy...Comment: framework for a system-level analysis of the power grid from the
viewpoint of complex network
Less is More: Real-time Failure Localization in Power Systems
Cascading failures in power systems exhibit non-local propagation patterns
which make the analysis and mitigation of failures difficult. In this work, we
propose a distributed control framework inspired by the recently proposed
concepts of unified controller and network tree-partition that offers strong
guarantees in both the mitigation and localization of cascading failures in
power systems. In this framework, the transmission network is partitioned into
several control areas which are connected in a tree structure, and the unified
controller is adopted by generators or controllable loads for fast timescale
disturbance response. After an initial failure, the proposed strategy always
prevents successive failures from happening, and regulates the system to the
desired steady state where the impact of initial failures are localized as much
as possible. For extreme failures that cannot be localized, the proposed
framework has a configurable design, that progressively involves and
coordinates more control areas for failure mitigation and, as a last resort,
imposes minimal load shedding. We compare the proposed control framework with
Automatic Generation Control (AGC) on the IEEE 118-bus test system. Simulation
results show that our novel framework greatly improves the system robustness in
terms of the N-1 security standard, and localizes the impact of initial
failures in majority of the load profiles that are examined. Moreover, the
proposed framework incurs significantly less load loss, if any, compared to
AGC, in all of our case studies
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