260,263 research outputs found
The Essential Role and the Continuous Evolution of Modulation Techniques for Voltage-Source Inverters in the Past, Present, and Future Power Electronics
The cost reduction of power-electronic devices, the increase in their reliability, efficiency, and power capability, and lower development times, together with more demanding application requirements, has driven the development of several new inverter topologies recently introduced in the industry, particularly medium-voltage converters. New more complex inverter topologies and new application fields come along with additional control challenges, such as voltage imbalances, power-quality issues, higher efficiency needs, and fault-tolerant operation, which necessarily requires the parallel development of modulation schemes. Therefore, recently, there have been significant advances in the field of modulation of dc/ac converters, which conceptually has been dominated during the last several decades almost exclusively by classic pulse-width modulation (PWM) methods. This paper aims to concentrate and discuss the latest developments on this exciting technology, to provide insight on where the state-of-the-art stands today, and analyze the trends and challenges driving its future
Calculation of solvency capital requirements for non-life underwriting risk using generalized linear models
The paper presents various GLM models using individual rating factors to calculate the solvency capital requirements for non-life underwriting risk in insurance. First, we consider the potential heterogeneity of claim frequency and the occurrence of large claims in the models. Second, we analyse how the distribution of frequency and severity varies depending on the modelling approach and examine how they are projected into SCR estimates according to the Solvency II Directive. In addition, we show that neglecting of large claims is as consequential as neglecting the heterogeneity of claim frequency. The claim frequency and severity are managed using generalized linear models, that is, negative-binomial and gamma regression. However, the different individual probabilities of large claims are represented by the binomial model and the large claim severity is managed using generalized Pareto distribution. The results are obtained and compared using the simulation of frequency-severity of an actual insurance portfolio.Web of Science26446645
On the Lie symmetries of a class of generalized Ermakov systems
The symmetry analysis of Ermakov systems is extended to the generalized case
where the frequency depends on the dynamical variables besides time. In this
extended framework, a whole class of nonlinearly coupled oscillators are viewed
as Hamiltonian Ermakov system and exactly solved in closed form
Geometric Objects: A Quality Index to Electromagnetic Energy Transfer Performance in Sustainable Smart Buildings
Sustainable smart buildings play an essential role in terms of more efficient energy.
However, these buildings as electric loads are affected by an important distortion in the current and
voltage waveforms caused by the increasing proliferation of nonlinear electronic devices. Overall,
buildings all around the world consume a significant amount of energy, which is about one-third of
the total primary energy resources. Optimization of the power transfer process of such amount of
energy is a crucial issue that needs specific tools to integrate energy-efficient behaviour throughout
the grid. When nonlinear loads are present, new capable ways of thinking are needed to consider
the effects of harmonics and related power components. In this manner, technology innovations are
necessary to update the power factor concept to a generalized total or a true one, where different
power components involved in it calculation, properly reflect each harmonic interaction. This work
addresses an innovative theory that applies the Poynting Vector philosophy via Geometric Algebra
to the electromagnetic energy transfer process providing a physical foundation. In this framework,
it is possible to analyse and detect the nature of disturbing loads in the exponential growth of
new globalized buildings and architectures in our era. This new insight is based on the concept
of geometric objects with different dimension: vector, bivector, trivector, multivector. Within this
paper, these objects are correlated with the electromagnetic quantities responsible for the energy flow
supplied to the most common loads in sustainable smart buildings. Besides, it must be considered
that these phenomena are characterized by a quality index multivector appropriate even for detecting
harmonic sources. A numerical example is used to illustrate the clear capabilities of the suggested
index when it applies to industrial loads for optimization of energy control systems and enhance
comfort management in smart sustainable buildings
Tomorrow's Metamaterials: Manipulation of Electromagnetic Waves in Space, Time and Spacetime
Metamaterials represent one of the most vibrant fields of modern science and
technology. They are generally dispersive structures in the direct and
reciprocal space and time domains. Upon this consideration, I overview here a
number of metamaterial innovations developed by colleagues and myself in the
holistic framework of space and time dispersion engineering. Moreover, I
provide some thoughts regarding the future perspectives of the area
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