10,698 research outputs found
Active actuator fault-tolerant control of a wind turbine benchmark model
This paper describes the design of an active fault-tolerant control scheme that is applied to the actuator of a
wind turbine benchmark. The methodology is based on adaptive filters obtained via the nonlinear geometric
approach, which allows to obtain interesting decoupling property with respect to uncertainty affecting the
wind turbine system. The controller accommodation scheme exploits the on-line estimate of the actuator
fault signal generated by the adaptive filters. The nonlinearity of the wind turbine model is described by the
mapping to the power conversion ratio from tip-speed ratio and blade pitch angles. This mapping represents
the aerodynamic uncertainty, and usually is not known in analytical form, but in general represented by
approximated two-dimensional maps (i.e. look-up tables). Therefore, this paper suggests a scheme to
estimate this power conversion ratio in an analytical form by means of a two-dimensional polynomial, which
is subsequently used for designing the active fault-tolerant control scheme. The wind turbine power generating
unit of a grid is considered as a benchmark to show the design procedure, including the aspects of
the nonlinear disturbance decoupling method, as well as the viability of the proposed approach. Extensive
simulations of the benchmark process are practical tools for assessing experimentally the features of the
developed actuator fault-tolerant control scheme, in the presence of modelling and measurement errors.
Comparisons with different fault-tolerant schemes serve to highlight the advantages and drawbacks of the
proposed methodology
Hamiltonian quantum simulation with bounded-strength controls
We propose dynamical control schemes for Hamiltonian simulation in many-body
quantum systems that avoid instantaneous control operations and rely solely on
realistic bounded-strength control Hamiltonians. Each simulation protocol
consists of periodic repetitions of a basic control block, constructed as a
suitable modification of an "Eulerian decoupling cycle," that would otherwise
implement a trivial (zero) target Hamiltonian. For an open quantum system
coupled to an uncontrollable environment, our approach may be employed to
engineer an effective evolution that simulates a target Hamiltonian on the
system, while suppressing unwanted decoherence to the leading order. We present
illustrative applications to both closed- and open-system simulation settings,
with emphasis on simulation of non-local (two-body) Hamiltonians using only
local (one-body) controls. In particular, we provide simulation schemes
applicable to Heisenberg-coupled spin chains exposed to general linear
decoherence, and show how to simulate Kitaev's honeycomb lattice Hamiltonian
starting from Ising-coupled qubits, as potentially relevant to the dynamical
generation of a topologically protected quantum memory. Additional implications
for quantum information processing are discussed.Comment: 24 pages, 5 color figure
Analog/RF Circuit Design Techniques for Nanometerscale IC Technologies
CMOS evolution introduces several problems in analog design. Gate-leakage mismatch exceeds conventional matching tolerances requiring active cancellation techniques or alternative architectures. One strategy to deal with the use of lower supply voltages is to operate critical parts at higher supply voltages, by exploiting combinations of thin- and thick-oxide transistors. Alternatively, low voltage circuit techniques are successfully developed. In order to benefit from nanometer scale CMOS technology, more functionality is shifted to the digital domain, including parts of the RF circuits. At the same time, analog control for digital and digital control for analog emerges to deal with current and upcoming imperfections
A review of convex approaches for control, observation and safety of linear parameter varying and Takagi-Sugeno systems
This paper provides a review about the concept of convex systems based on Takagi-Sugeno, linear parameter varying (LPV) and quasi-LPV modeling. These paradigms are capable of hiding the nonlinearities by means of an equivalent description which uses a set of linear models interpolated by appropriately defined weighing functions. Convex systems have become very popular since they allow applying extended linear techniques based on linear matrix inequalities (LMIs) to complex nonlinear systems. This survey aims at providing the reader with a significant overview of the existing LMI-based techniques for convex systems in the fields of control, observation and safety. Firstly, a detailed review of stability, feedback, tracking and model predictive control (MPC) convex controllers is considered. Secondly, the problem of state estimation is addressed through the design of proportional, proportional-integral, unknown input and descriptor observers. Finally, safety of convex systems is discussed by describing popular techniques for fault diagnosis and fault tolerant control (FTC).Peer ReviewedPostprint (published version
Power Converters and Power Quality
This paper discusses the subject of power quality for power converters. The
first part gives an overview of most of the common disturbances and power
quality issues in electrical networks for particle accelerators, and explains
their consequences for accelerator operation. The propagation of asymmetrical
network disturbances into a network is analysed. Quantitative parameters for
network disturbances in a typical network are presented, and immunity levels
for users' electrical equipment are proposed. The second part of this paper
discusses the technologies and strategies used in particle accelerator networks
for power quality improvement. Particular focus is given to networks supplying
loads with cycling active and reactive power.Comment: 26 pages, contribution to the 2014 CAS - CERN Accelerator School:
Power Converters, Baden, Switzerland, 7-14 May 201
Cosmic Acceleration and the Helicity-0 Graviton
We explore cosmology in the decoupling limit of a non-linear covariant
extension of Fierz-Pauli massive gravity obtained recently in arXiv:1007.0443.
In this limit the theory is a scalar-tensor model of a unique form defined by
symmetries. We find that it admits a self-accelerated solution, with the Hubble
parameter set by the graviton mass. The negative pressure causing the
acceleration is due to a condensate of the helicity-0 component of the massive
graviton, and the background evolution, in the approximation used, is
indistinguishable from the \Lambda CDM model. Fluctuations about the
self-accelerated background are stable for a certain range of parameters
involved. Most surprisingly, the fluctuation of the helicity-0 field above its
background decouples from an arbitrary source in the linearized theory. We also
show how massive gravity can remarkably screen an arbitrarily large
cosmological constant in the decoupling limit, while evading issues with
ghosts. The obtained static solution is stable against small perturbations,
suggesting that the degravitation of the vacuum energy is possible in the full
theory. Interestingly, however, this mechanism postpones the Vainshtein effect
to shorter distance scales. Hence, fifth force measurements severely constrain
the value of the cosmological constant that can be neutralized, making this
scheme phenomenologically not viable for solving the old cosmological constant
problem. We briefly speculate on a possible way out of this issue.Comment: v2: improved discussion and referencin
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