1,472 research outputs found
ESPRIT for multidimensional general grids
We present a new method for complex frequency estimation in several
variables, extending the classical (1d) ESPRIT-algorithm. We also consider how
to work with data sampled on non-standard domains (i.e going beyond
multi-rectangles)
Revisiting the Merit-Order Effect of Renewable Energy Sources
An on-going debate in the energy economics and power market community has
raised the question if energy-only power markets are increasingly failing due
to growing feed-in shares from subsidized renewable energy sources (RES). The
short answer to this is: No, they are not failing. Energy-based power markets
are, however, facing several market distortions, namely from the gap between
the electricity volume traded at day-ahead markets versus the overall
electricity consumption as well as the (wrong) regulatory assumption that
variable RES generation, i.e., wind and photovoltaic (PV), truly have zero
marginal operation costs. In this paper we show that both effects over-amplify
the well-known merit-order effect of RES power feed-in beyond a level that is
explainable by underlying physical realities, i.e., thermal power plants being
willing to accept negative electricity prices to be able to stay online due to
considerations of wear & tear and start-stop constraints. We analyze the
impacts of wind and PV power feed-in on the day-ahead market for a region that
is already today experiencing significant feed-in tariff (FIT)-subsidized RES
power feed-in, the EPEX German-Austrian market zone (20% FIT share).
Our analysis shows that, if the necessary regulatory adaptations are taken,
i.e., increasing the day-ahead market's share of overall load demand and using
the true marginal costs of RES units in the merit-order, energy-based power
markets can remain functional despite high RES power feed-in.Comment: Working Paper (9 pages, 11 figures, 5 tables) - Some revisions since
last version (10 February 2014). (Under 2nd review for IEEE Transactions on
Power Systems
Fast algorithms and efficient GPU implementations for the Radon transform and the back-projection operator represented as convolution operators
The Radon transform and its adjoint, the back-projection operator, can both
be expressed as convolutions in log-polar coordinates. Hence, fast algorithms
for the application of the operators can be constructed by using FFT, if data
is resampled at log-polar coordinates. Radon data is typically measured on an
equally spaced grid in polar coordinates, and reconstructions are represented
(as images) in Cartesian coordinates. Therefore, in addition to FFT, several
steps of interpolation have to be conducted in order to apply the Radon
transform and the back-projection operator by means of convolutions.
Both the interpolation and the FFT operations can be efficiently implemented
on Graphical Processor Units (GPUs). For the interpolation, it is possible to
make use of the fact that linear interpolation is hard-wired on GPUs, meaning
that it has the same computational cost as direct memory access. Cubic order
interpolation schemes can be constructed by combining linear interpolation
steps which provides important computation speedup.
We provide details about how the Radon transform and the back-projection can
be implemented efficiently as convolution operators on GPUs. For large data
sizes, speedups of about 10 times are obtained in relation to the computational
times of other software packages based on GPU implementations of the Radon
transform and the back-projection operator. Moreover, speedups of more than a
1000 times are obtained against the CPU-implementations provided in the MATLAB
image processing toolbox
Non-Convex Rank/Sparsity Regularization and Local Minima
This paper considers the problem of recovering either a low rank matrix or a
sparse vector from observations of linear combinations of the vector or matrix
elements. Recent methods replace the non-convex regularization with or
nuclear norm relaxations. It is well known that this approach can be guaranteed
to recover a near optimal solutions if a so called restricted isometry property
(RIP) holds. On the other hand it is also known to perform soft thresholding
which results in a shrinking bias which can degrade the solution.
In this paper we study an alternative non-convex regularization term. This
formulation does not penalize elements that are larger than a certain threshold
making it much less prone to small solutions. Our main theoretical results show
that if a RIP holds then the stationary points are often well separated, in the
sense that their differences must be of high cardinality/rank. Thus, with a
suitable initial solution the approach is unlikely to fall into a bad local
minima. Our numerical tests show that the approach is likely to converge to a
better solution than standard /nuclear-norm relaxation even when
starting from trivial initializations. In many cases our results can also be
used to verify global optimality of our method
Grid Integration Costs of Fluctuating Renewable Energy Sources
The grid integration of intermittent Renewable Energy Sources (RES) causes
costs for grid operators due to forecast uncertainty and the resulting
production schedule mismatches. These so-called profile service costs are
marginal cost components and can be understood as an insurance fee against RES
production schedule uncertainty that the system operator incurs due to the
obligation to always provide sufficient control reserve capacity for power
imbalance mitigation. This paper studies the situation for the German power
system and the existing German RES support schemes. The profile service costs
incurred by German Transmission System Operators (TSOs) are quantified and
means for cost reduction are discussed. In general, profile service costs are
dependent on the RES prediction error and the specific workings of the power
markets via which the prediction error is balanced. This paper shows both how
the prediction error can be reduced in daily operation as well as how profile
service costs can be reduced via optimization against power markets and/or
active curtailment of RES generation.Comment: Accepted for SUSTECH 2014, Portland, Oregon, USA, July 201
Four-dimensional tomographic reconstruction by time domain decomposition
Since the beginnings of tomography, the requirement that the sample does not
change during the acquisition of one tomographic rotation is unchanged. We
derived and successfully implemented a tomographic reconstruction method which
relaxes this decades-old requirement of static samples. In the presented
method, dynamic tomographic data sets are decomposed in the temporal domain
using basis functions and deploying an L1 regularization technique where the
penalty factor is taken for spatial and temporal derivatives. We implemented
the iterative algorithm for solving the regularization problem on modern GPU
systems to demonstrate its practical use
Fast hyperbolic Radon transform represented as convolutions in log-polar coordinates
The hyperbolic Radon transform is a commonly used tool in seismic processing,
for instance in seismic velocity analysis, data interpolation and for multiple
removal. A direct implementation by summation of traces with different moveouts
is computationally expensive for large data sets. In this paper we present a
new method for fast computation of the hyperbolic Radon transforms. It is based
on using a log-polar sampling with which the main computational parts reduce to
computing convolutions. This allows for fast implementations by means of FFT.
In addition to the FFT operations, interpolation procedures are required for
switching between coordinates in the time-offset; Radon; and log-polar domains.
Graphical Processor Units (GPUs) are suitable to use as a computational
platform for this purpose, due to the hardware supported interpolation routines
as well as optimized routines for FFT. Performance tests show large speed-ups
of the proposed algorithm. Hence, it is suitable to use in iterative methods,
and we provide examples for data interpolation and multiple removal using this
approach.Comment: 21 pages, 10 figures, 2 table
Realisering av PLC-system och simulering med mikrokontroller
The purpose of this thesis with the conversion of the industrial press for centrumbrick on Höganäs Bjuf AB was to improve the security for the work- and maintenance personnel. To improve the security a new control system containing a PLC based control logic and HMI was developed. The new control system will improve the work security for the maintenance personal because the operating voltage for sensors on the machine will be lowered to 24VDC. At the same time the new control system allows new safety precautions as a two hand control to be implemented. To test the functionality of the new control system a simulation environment was developed. The simulation environment was implemented on a microcontroller of the model Arduino Mega 2560. This microcontroller was programmed to reflect the manufacturing process in a realistic way. All the software that has been used to develop the PLC program, HMI and the simulation environment is described in the report. Software that has been used is GxWorks2, iX Developer and Atmel studio
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