308 research outputs found
A minimalistic approach to appearance-based visual SLAM
This paper presents a vision-based approach to SLAM in indoor / outdoor environments with minimalistic sensing and computational requirements. The approach is based on a graph representation of robot poses, using a relaxation algorithm to obtain a globally consistent map. Each link corresponds to a
relative measurement of the spatial relation between the two nodes it connects. The links describe the likelihood distribution of the relative pose as a Gaussian distribution. To estimate the covariance matrix for links obtained from an omni-directional vision sensor, a novel method is introduced based on the relative similarity of neighbouring images. This new method does not require determining distances to image features using multiple
view geometry, for example. Combined indoor and outdoor experiments demonstrate that the approach can handle qualitatively different environments (without modification of the parameters), that it can cope with violations of the âflat floor assumptionâ to some degree, and that it scales well with increasing size of the environment, producing topologically correct and geometrically accurate maps at low computational cost. Further experiments demonstrate that the approach is also suitable for combining multiple overlapping maps, e.g. for solving the multi-robot SLAM problem with unknown initial poses
Control of MTDC Transmission Systems under Local Information
High-voltage direct current (HVDC) is a commonly used technology for
long-distance electric power transmission, mainly due to its low resistive
losses. In this paper a distributed controller for multi-terminal high-voltage
direct current (MTDC) transmission systems is considered. Sufficient conditions
for when the proposed controller renders the closed-loop system asymptotically
stable are provided. Provided that the closed loop system is asymptotically
stable, it is shown that in steady-state a weighted average of the deviations
from the nominal voltages is zero. Furthermore, a quadratic cost of the current
injections is minimized asymptotically
Distributed PI-Control with Applications to Power Systems Frequency Control
This paper considers a distributed PI-controller for networked dynamical
systems. Sufficient conditions for when the controller is able to stabilize a
general linear system and eliminate static control errors are presented. The
proposed controller is applied to frequency control of power transmission
systems. Sufficient stability criteria are derived, and it is shown that the
controller parameters can always be chosen so that the frequencies in the
closed loop converge to nominal operational frequency. We show that the load
sharing property of the generators is maintained, i.e., the input power of the
generators is proportional to a controller parameter. The controller is
evaluated by simulation on the IEEE 30 bus test network, where its
effectiveness is demonstrated
Distributed Voltage and Current Control of Multi-Terminal High-Voltage Direct Current Transmission Systems
High-voltage direct current (HVDC) is a commonly used technology for
long-distance power transmission, due to its low resistive losses and low
costs. In this paper, a novel distributed controller for multi-terminal HVDC
(MTDC) systems is proposed. Under certain conditions on the controller gains,
it is shown to stabilize the MTDC system. The controller is shown to always
keep the voltages close to the nominal voltage, while assuring that the
injected power is shared fairly among the converters. The theoretical results
are validated by simulations, where the affect of communication time-delays is
also studied
Hur kan producentkooperativa företag utforma sina nyckeltal sÄ att de Àr anpassade till företagets vision och styrelsens intressen? - en fallstudie av SkÄnemejerier
Syftet med uppsatsen Àr att utforma en teoretisk nyckeltalsmodell som Àr lÀmplig att anvÀnda i ett producentkooperativ och som Àr anpassade för företagets vision och styrelsens intressen. Detta utför vi med hjÀlp av en fallstudie dÄ vi valt ett kvalitativt och abduktivt angreppssÀtt. För insamling av empiri har vi i vÄrt fallföretag utfört djupintervjuer. De teorier vi valt att arbeta med Àr; agentteorin, nyckeltal, Balanced Scorecard samt producentkooperativ. Resultatet av vÄr insamlade empiri och den teori vi valt att fokusera pÄ har mynnat ut i att vi har konstruerat ett Balanced Scorecard anpassat till ett producentkooperativ vilket underlÀttar uppföljningen mellan ledning och styrelse
Distributed Controllers for Multi-Terminal HVDC Transmission Systems
High-voltage direct current (HVDC) is an increasingly commonly used
technology for long-distance electric power transmission, mainly due to its low
resistive losses. In this paper the voltage-droop method (VDM) is reviewed, and
three novel distributed controllers for multi-terminal HVDC (MTDC) transmission
systems are proposed. Sufficient conditions for when the proposed controllers
render the equilibrium of the closed-loop system asymptotically stable are
provided. These conditions give insight into suitable controller architecture,
e.g., that the communication graph should be identical with the graph of the
MTDC system, including edge weights. Provided that the equilibria of the
closed-loop systems are asymptotically stable, it is shown that the voltages
asymptotically converge to within predefined bounds. Furthermore, a quadratic
cost of the injected currents is asymptotically minimized. The proposed
controllers are evaluated on a four-bus MTDC system.Comment: arXiv admin note: substantial text overlap with arXiv:1406.5839,
arXiv:1311.514
Lidar-level localization with radar? The CFEAR approach to accurate, fast and robust large-scale radar odometry in diverse environments
This paper presents an accurate, highly efficient, and learning-free method
for large-scale odometry estimation using spinning radar, empirically found to
generalize well across very diverse environments -- outdoors, from urban to
woodland, and indoors in warehouses and mines - without changing parameters.
Our method integrates motion compensation within a sweep with one-to-many scan
registration that minimizes distances between nearby oriented surface points
and mitigates outliers with a robust loss function. Extending our previous
approach CFEAR, we present an in-depth investigation on a wider range of data
sets, quantifying the importance of filtering, resolution, registration cost
and loss functions, keyframe history, and motion compensation. We present a new
solving strategy and configuration that overcomes previous issues with sparsity
and bias, and improves our state-of-the-art by 38%, thus, surprisingly,
outperforming radar SLAM and approaching lidar SLAM. The most accurate
configuration achieves 1.09% error at 5Hz on the Oxford benchmark, and the
fastest achieves 1.79% error at 160Hz.Comment: Accepted for publication in Transactions on Robotics. Edited
2022-11-07: Updated affiliation and citatio
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