64,812 research outputs found
A Scalable Semidefinite Relaxation Approach to Grid Scheduling
Determination of the most economic strategies for supply and transmission of
electricity is a daunting computational challenge. Due to theoretical barriers,
so-called NP-hardness, the amount of effort to optimize the schedule of
generating units and route of power, can grow exponentially with the number of
decision variables. Practical approaches to this problem involve legacy
approximations and ad-hoc heuristics that may undermine the efficiency and
reliability of power system operations, that are ever growing in scale and
complexity. Therefore, the development of powerful optimization methods for
detailed power system scheduling is critical to the realization of smart grids
and has received significant attention recently. In this paper, we propose for
the first time a computational method, which is capable of solving large-scale
power system scheduling problems with thousands of generating units, while
accurately incorporating the nonlinear equations that govern the flow of
electricity on the grid. The utilization of this accurate nonlinear model, as
opposed to its linear approximations, results in a more efficient and
transparent market design, as well as improvements in the reliability of power
system operations. We design a polynomial-time solvable third-order
semidefinite programming (TSDP) relaxation, with the aim of finding a near
globally optimal solution for the original NP-hard problem. The proposed method
is demonstrated on the largest available benchmark instances from real-world
European grid data, for which provably optimal or near-optimal solutions are
obtained
Real-Time Stochastic Optimal Control for Multi-agent Quadrotor Systems
This paper presents a novel method for controlling teams of unmanned aerial
vehicles using Stochastic Optimal Control (SOC) theory. The approach consists
of a centralized high-level planner that computes optimal state trajectories as
velocity sequences, and a platform-specific low-level controller which ensures
that these velocity sequences are met. The planning task is expressed as a
centralized path-integral control problem, for which optimal control
computation corresponds to a probabilistic inference problem that can be solved
by efficient sampling methods. Through simulation we show that our SOC approach
(a) has significant benefits compared to deterministic control and other SOC
methods in multimodal problems with noise-dependent optimal solutions, (b) is
capable of controlling a large number of platforms in real-time, and (c) yields
collective emergent behaviour in the form of flight formations. Finally, we
show that our approach works for real platforms, by controlling a team of three
quadrotors in outdoor conditions.Comment: 17 pages, 8 figures, 26th International Conference on Automated
Planning and Schedulin
On the Flow Problem in Water Distribution Networks: Uniqueness and Solvers
Increasing concerns on the security and quality of water distribution systems
(WDS), along with their role as smart city components, call for computational
tools with performance guarantees. To this end, this work revisits the physical
laws governing water flow and provides a hierarchy of solvers having
complementary value. Given water injections in a WDS, finding the corresponding
water flows within pipes and pumps together with the pressures at all nodes
constitutes the water flow (WF) problem. The latter entails solving a set of
(non)-linear equations. It is shown that the WF problem admits a unique
solution even in networks hosting pumps. For networks without pumps, the WF
solution can be recovered as the minimizer of a convex energy function. The
latter approach is extended to networks with pumps but not in cycles, through a
stitching algorithm. For networks with non-overlapping cycles, a provably exact
convex relaxation of the pressure drop equations yields a mixed-integer
quadratic program (MIQP)-based WF solver. A hybrid scheme combining the MIQP
with the stitching algorithm can handle water networks with overlapping cycles,
but without pumps on them. Each solver is guaranteed to converge regardless
initialization. Two of the solvers are numerically validated on a benchmark
WDS
Context-Aware System Synthesis, Task Assignment, and Routing
The design and organization of complex robotic systems traditionally requires
laborious trial-and-error processes to ensure both hardware and software
components are correctly connected with the resources necessary for
computation. This paper presents a novel generalization of the quadratic
assignment and routing problem, introducing formalisms for selecting components
and interconnections to synthesize a complete system capable of providing some
user-defined functionality. By introducing mission context, functional
requirements, and modularity directly into the assignment problem, we derive a
solution where components are automatically selected and then organized into an
optimal hardware and software interconnection structure, all while respecting
restrictions on component viability and required functionality. The ability to
generate \emph{complete} functional systems directly from individual components
reduces manual design effort by allowing for a guided exploration of the design
space. Additionally, our formulation increases resiliency by quantifying
resource margins and enabling adaptation of system structure in response to
changing environments, hardware or software failure. The proposed formulation
is cast as an integer linear program which is provably -hard. Two
case studies are developed and analyzed to highlight the expressiveness and
complexity of problems that can be addressed by this approach: the first
explores the iterative development of a ground-based search-and-rescue robot in
a variety of mission contexts, while the second explores the large-scale,
complex design of a humanoid disaster robot for the DARPA Robotics Challenge.
Numerical simulations quantify real world performance and demonstrate tractable
time complexity for the scale of problems encountered in many modern robotic
systems.Comment: 17 pages, 10 figures, Submitted to Transactions in Robotic
A Convex Optimization Approach to Smooth Trajectories for Motion Planning with Car-Like Robots
In the recent past, several sampling-based algorithms have been proposed to
compute trajectories that are collision-free and dynamically-feasible. However,
the outputs of such algorithms are notoriously jagged. In this paper, by
focusing on robots with car-like dynamics, we present a fast and simple
heuristic algorithm, named Convex Elastic Smoothing (CES) algorithm, for
trajectory smoothing and speed optimization. The CES algorithm is inspired by
earlier work on elastic band planning and iteratively performs shape and speed
optimization. The key feature of the algorithm is that both optimization
problems can be solved via convex programming, making CES particularly fast. A
range of numerical experiments show that the CES algorithm returns high-quality
solutions in a matter of a few hundreds of milliseconds and hence appears
amenable to a real-time implementation
Efficient Model Identification for Tensegrity Locomotion
This paper aims to identify in a practical manner unknown physical
parameters, such as mechanical models of actuated robot links, which are
critical in dynamical robotic tasks. Key features include the use of an
off-the-shelf physics engine and the Bayesian optimization framework. The task
being considered is locomotion with a high-dimensional, compliant Tensegrity
robot. A key insight, in this case, is the need to project the model
identification challenge into an appropriate lower dimensional space for
efficiency. Comparisons with alternatives indicate that the proposed method can
identify the parameters more accurately within the given time budget, which
also results in more precise locomotion control
Thermal Transients in District Heating Systems
Heat fluxes in a district heating pipeline systems need to be controlled on
the scale from minutes to an hour to adjust to evolving demand. There are two
principal ways to control the heat flux - keep temperature fixed but adjust
velocity of the carrier (typically water) or keep the velocity flow steady but
then adjust temperature at the heat producing source (heat plant). We study the
latter scenario, commonly used for operations in Russia and Nordic countries,
and analyze dynamics of the heat front as it propagates through the system.
Steady velocity flows in the district heating pipelines are typically turbulent
and incompressible. Changes in the heat, on either consumption or production
sides, lead to slow transients which last from tens of minutes to hours. We
classify relevant physical phenomena in a single pipe, e.g. turbulent spread of
the turbulent front. We then explain how to describe dynamics of temperature
and heat flux evolution over a network efficiently and illustrate the network
solution on a simple example involving one producer and one consumer of heat
connected by "hot" and "cold" pipes. We conclude the manuscript motivating
future research directions.Comment: 31 pages, 7 figure
The role of intelligent systems in delivering the smart grid
The development of "smart" or "intelligent" energy networks has been proposed by both EPRI's IntelliGrid initiative and the European SmartGrids Technology Platform as a key step in meeting our future energy needs. A central challenge in delivering the energy networks of the future is the judicious selection and development of an appropriate set of technologies and techniques which will form "a toolbox of proven technical solutions". This paper considers functionality required to deliver key parts of the Smart Grid vision of future energy networks. The role of intelligent systems in providing these networks with the requisite decision-making functionality is discussed. In addition to that functionality, the paper considers the role of intelligent systems, in particular multi-agent systems, in providing flexible and extensible architectures for deploying intelligence within the Smart Grid. Beyond exploiting intelligent systems as architectural elements of the Smart Grid, with the purpose of meeting a set of engineering requirements, the role of intelligent systems as a tool for understanding what those requirements are in the first instance, is also briefly discussed
A SPEA2 Based Planning Framework for Optimal Integration of Distributed Generations
The paper presents a multi-objective optimisation method for analysing the best mix of renewable and non- renewable distributed generations (DG) in a distribution network. The method aims at minimising the total cost of the real power generation, line losses and CO2 emissions, and maximising the benefits from DG installations over a planning horizon of 20 years. The paper proposes new objective functions that take into account the longevity of DG operations as one of its selection criteria. The analysis utilises the Strength Pareto Evolutionary Algorithm 2 (SPEA2) for optimisation and MATPOWER for solving the optimal power flow problems
A Survey of Learning in Multiagent Environments: Dealing with Non-Stationarity
The key challenge in multiagent learning is learning a best response to the
behaviour of other agents, which may be non-stationary: if the other agents
adapt their strategy as well, the learning target moves. Disparate streams of
research have approached non-stationarity from several angles, which make a
variety of implicit assumptions that make it hard to keep an overview of the
state of the art and to validate the innovation and significance of new works.
This survey presents a coherent overview of work that addresses
opponent-induced non-stationarity with tools from game theory, reinforcement
learning and multi-armed bandits. Further, we reflect on the principle
approaches how algorithms model and cope with this non-stationarity, arriving
at a new framework and five categories (in increasing order of sophistication):
ignore, forget, respond to target models, learn models, and theory of mind. A
wide range of state-of-the-art algorithms is classified into a taxonomy, using
these categories and key characteristics of the environment (e.g.,
observability) and adaptation behaviour of the opponents (e.g., smooth,
abrupt). To clarify even further we present illustrative variations of one
domain, contrasting the strengths and limitations of each category. Finally, we
discuss in which environments the different approaches yield most merit, and
point to promising avenues of future research.Comment: 64 pages, 7 figures. Under review since November 201
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