Search

This study investigates modelling of doubly-fed induction generator (DFIG)-based wind turbines for low-frequency oscillation analysis of power systems with high penetration of distributed energy. A reduced order model of wind turbine with DFIG is proposed for small signal stability analysis in electromechanical time scale for low-frequency oscillation analysis. Furthermore, a Thévenin equivalent model of DFIG with internal voltage is also presented. Base on the derived model, the effect of phase-locked loop is emphasised, and explained by using the internal voltage derived. The model proposed is well verified by modal analysis and time-domain simulations. [ABSTRACT FROM AUTHOR]

This study investigates modelling of doubly-fed induction generator (DFIG)-based wind turbines for low-frequency oscillation analysis of power systems with high penetration of distributed energy. A reduced order model of wind turbine with DFIG is proposed for small signal stability analysis in electromechanical time scale for low-frequency oscillation analysis. Furthermore, a Thévenin equivalent model of DFIG with internal voltage is also presented. Base on the derived model, the effect of phase-locked loop is emphasised, and explained by using the internal voltage derived. The model proposed is well verified by modal analysis and time-domain simulations.

Microplastics (MPs) in the environment are the sink and vector of organic contaminants, including per- and polyfluoroalkyl substances (PFASs). Although PFASs are low- and non-volatile compounds, they have the potential to partition and diffuse from MP into the gas phase in the environmental functions. Herein, the MP-air partition coefficient (K PA) of seven PFASs was measured using a solid-fugacity meter. The PFAS K PA values in two MPs (high-density polyethylene (HDPE) and thermoplastic polyurethane (TPU)) were determined under different times, temperatures, and relative humidities (RH), and a model was developed to predict the PFAS K PA values based on the measured data. The results showed that the K PA of PFASs increased with the prolonged partition time until 90 mins, and higher temperature and RH facilitated the distribution of PFASs in MPs into the air phase, leading to smaller K PA values. Moreover, the derived equation for predicting PFAS log K PA values was robust with 0.79 of an adjusted square of correlation coefficient (R2 adjusted = 0.79) and 0.35 of root mean squared error (RMSE = 0.35). These findings provided the first knowledge for understanding the partition behavior and fate of PFASs in the MP-air microenvironment. [Display omitted] • The K PA of seven PFASs was determined at environmentally relative conditions through a solid-fugacity meter. • The partition of PFASs between MPs and gas was equilibrium when partition time reached 90 mins. • Increasing temperature and RH resulted in the reduction of PFAS K PA. • A derived model based on the measured data could effectively predict the K PA of PFAS. [ABSTRACT FROM AUTHOR]

The purpose of the paper is to discuss ten things potential users should know about the limits of the Dynamic Conditional Correlation (DCC) representation for estimating and forecasting time-varying conditional correlations. The reasons given for caution about the use of DCC include the following: DCC represents the dynamic conditional covariances of the standardized residuals, and hence does not yield dynamic conditional correlations; DCC is stated rather than derived; DCC has no moments; DCC does not have testable regularity conditions; DCC yields inconsistent two step estimators; DCC has no asymptotic properties; DCC is not a special case of Generalized Autoregressive Conditional Correlation (GARCC), which has testable regularity conditions and standard asymptotic properties; DCC is not dynamic empirically as the effect of news is typically extremely small; DCC cannot be distinguished empirically from diagonal Baba, Engle, Kraft and Kroner (BEKK) in small systems; and DCC may be a useful filter or a diagnostic check, but it is not a model.

Given an inductive-like pointclass Γ ˜ and assuming the Axiom of Determinacy, Martin identified and analyzed a pointclass that contains the prewellorderings of the next scale beyond Γ ˜ if such a scale exists. We show that much of Martin's analysis can be carried out assuming only ZF + DC R and Δ ˜ Γ ˜ determinacy by adapting arguments of Kechris and Woodin [10] and Martin [13] . This generalization can be used to show that every set of reals is Suslin in the intersection of two divergent models of A D + , giving a new proof of a theorem of Woodin, as well as to show that every set of reals is Suslin in the derived model at an indestructibly weakly compact limit of Woodin cardinals. [ABSTRACT FROM AUTHOR]

In this paper, we explore the structure theory of L(ℝ, μ) under the hypothesis L(ℝ, μ) ⊧ “AD + μ is a normal fine measure on ” and give some applications. First we show that “ ZFC + there exist ω2 Woodin cardinals”1 has the same consistency strength as “ AD + ω1 is ℝ-supercompact”. During this process we show that if L(ℝ, μ) ⊧ AD then in fact L(ℝ, μ) ⊧ AD+. Next we prove important properties of L(ℝ, μ) including Σ1 -reflection and the uniqueness of μ in L(ℝ, μ). Then we give the computation of full HOD in L(ℝ, μ). Finally, we use Σ1 -reflection and ℙmax forcing to construct a certain ideal on (or equivalently on in this situation) that has the same consistency strength as “ZFC+ there exist ω2 Woodin cardinals.” [ABSTRACT FROM PUBLISHER]

In order to further complement the system of grey power models, this paper analyzes the transformation relationships between the classic GM(1,1) model and GM(1,1) power model, and deduces five derived models including GM(1,1,x(2)) power model, GM(1,1,x(1)) power model, GM(1,1,6) power model, GM(1,1,exp) power model and GM(1,1,C) power model based on the defined and whitened GM(1,1) power models. A group of grey power models including classic GM(1,1) power model and the derived five models is built finally. The results show that time response functions of GM(1,1) model and GM(1,1) power model are essentially the same. Different derived models have different structures, contents and solutions, reflecting the principal of non-unique solution in grey system theory. In practical applications, the most appropriate whitened solution can be identified from group of default solutions under the corresponding objectives. [ABSTRACT FROM AUTHOR]

Grey resource efficacy model is effective for describing the developing stage (rapid varying phase) of resource efficacy S curve. In order to further complement the model system, this paper deduces five derived models based on the original resource efficacy model proposed by Professor Deng. The properties of these derived models are then studied respectively. The results show that different models have different structures, contents, solutions and properties, implying the principal of non-uniqueness in grey system theory. [ABSTRACT FROM AUTHOR]

Thin films of the promising Diisopropylammonium Bromide (α-DIPAB) are synthesized by the slow evaporation technique. We report on the synthesis and characterization of as-grown (α-DIPAB) thin films. In particular, structural, crystallographic, electronic, chemical, and optical properties are measured and interpreted. To elucidate structural and crystallographic properties, X-ray diffraction (XRD) measurements are conducted to reveal that α-DIPAB thin film is polycrystalline and exhibits a monoclinic structure. Furthermore, Density Functional Theory (DFT)-based simulations are performed to calculate the structural and electronic parameters of the α-DIPAB thin film. An excellent agreement between the measured and calculated structural parameters is obtained. Taking into account the Van der Waals forces using the HSE06 method yields an optical band gap (≈6 eV) in good agreement with the experimental value. Scanning Electronic Microscopy (SEM) micrographs demonstrate that thin-film surface cracks appear dividing the surface into ice land-like regions. The coarse features in the short-scaled micrograph are characterized by the micro-sheet-like with cracked boundaries. Moreover, the role of the interactions between molecules mediated by bromine ions is revealed. The vibrational spectra correspond to a well-ordered crystal. The mechanism behind the large spontaneous polarization of thin films is explained. The interplay between electronic and optical properties of thin films is investigated using UV-Vis measurements and the recently published mathematical derived model. An excellent agreement between measured and calculated electronic and optical parameters indicates the validity and feasibility of the model. [ABSTRACT FROM AUTHOR]