863 research outputs found
Real-Time Prediction of Power Electronic Device Temperatures Using PRBS-Generated Frequency-Domain Thermal Cross Coupling Characteristics
This paper presents a technique to predict the temperature response of a multielement thermal system based on the thermal cross coupling between elements. The complex frequency-domain cross coupling of devices is first characterized using a pseudorandom binary sequence technique. The characteristics are then used to predict device temperatures for a known input power waveform using a discrete Fourier transform-based technique. The resulting prediction shows good agreement with an example practical system used for evaluation. To reduce the computational complexity of the initial method, a digital infinite impedance response (IIR) filter is fitted to each cross coupling characteristic. A high correlation fit is demonstrated that produces a near-identical temperature response compared to the initial procedure while requiring fewer mathematical operations. Experimental validation on the practical system shows good agreement between IIR filter predictions and practical results. It is further demonstrated that this agreement can be substantially improved by taking feedback from an internal reference temperature. Additionally, the proposed IIR filter technique allows the efficient calculation of future device temperatures based on simulated input, facilitating future temperature predictions
Real-time temperature estimation in a multiple device power electronics system subject to dynamic cooling
This paper presents a technique to estimate the temperature of each power electronic device in a thermally coupled, multiple device system subject to dynamic cooling. Using a demonstrator system, the thermal transfer impedance between pairs of devices is determined in the frequency domain for a quantised range of active cooling levels using a technique based on pseudorandom binary sequences. The technique is illustrated by application to the case temperatures of power devices. For each cooling level and pair of devices, a sixth order digital IIR filter is produced which can be used to directly estimate temperature from device input power. When the cooling level changes, the filters in use are substituted and the internal states of the old filters are converted for use in the new filter. Two methods for filter state conversion are developed—a computationally efficient method which is suited to infrequent changes in power dissipation and cooling, and a more accurate method which requires increased memory and processing capacity. Results show that the temperature can be estimated with low error using a system which is suitable for integration on an embedded processor
Critical Design Criterion for Achieving Zero Voltage Switching in Inductorless Half-Bridge-Driven Piezoelectric-Transformer-Based Power Supplies
A methodology for predicting the ability of inductor-less driven piezoelectric transformer (PT) based power supplies to achieve zero voltage switching (ZVS) is presented. A describing function approach is used to derive an equivalent circuit model of the PT operating in the vicinity of ZVS and the subsequent application of the model provides a quantitative measure of a PT's ability to achieve ZVS when driven by an inductor-less half-bridge inverter. Through detailed analysis of the analytical model, the limitations of the inductor-less half-bridge driven PT are exposed from which guidelines for designing both the PT and inverter are derived
201 INVESTIGATING SUPEROXIDE DISMUTASE EXPRESSION IN CARTILAGE AND A POTENTIAL ROLE IN OSTEOARTHRITIS
Equivalent circuit parameter extraction of low-capacitance high-damping PTs
Existing equivalent circuit extraction techniques are inaccurate for piezoelectric transformers (PTs) with low-input capacitance or high damping. A new method is presented, offering improved accuracy in both damping resistance and resonant frequency extraction compared with state-of-the-art methods. Effectiveness is evaluated on two sample PTs, with the proposed method achieving up to 84% decrease in error compared with previous methods
Influence of spurious modes on the efficiency of piezoelectric transformers : a sensitivity analysis
PLL controller for achieving zero-voltage switching (ZVS) in inductorless half-bridge drive piezoelectric transformer resonant power supplies
Inductorless half-bridge, piezoelectric transformer (PT) resonant power supplies require careful control if zero voltage switching of the MOSFETs is to be achieved. Here we describe how a phase-locked loop may be used to achieve this by ensuring adequate deadtime exists between the two MOSFETs to allow the PT input voltage to fully charge to the DC link. Experimental results demonstrate the operation of the system
Finite Temperature and Density Effect on Symmetry Breaking by Wilson Loops
A finite temperature and density effect of Wilson loop elements on non-simply
connected space is investigated in the model suggested by Hosotani. Using
one-loop calculations it is shown that the value of an "order parameter" does
not shift as the temperature grows. We find that finite density effect is of
much importance for restoration of symmetry.Comment: 11pages, no figur
On the radial expansion of tubular structures in a quark gluon plasma
We study the radial expansion of cylindrical tubes in a hot QGP. These tubes
are treated as perturbations in the energy density of the system which is
formed in heavy ion collisions at RHIC and LHC. We start from the equations of
relativistic hydrodynamics in two spatial dimensions and cylindrical symmetry
and perform an expansion of these equations in a small parameter, conserving
the nonlinearity of the hydrodynamical formalism. We consider both ideal and
viscous fluids and the latter are studied with a relativistic Navier-Stokes
equation. We use the equation of state of the MIT bag model. In the case of
ideal fluids we obtain a breaking wave equation for the energy density
fluctuation, which is then solved numerically. We also show that, under certain
assumptions, perturbations in a relativistic viscous fluid are governed by the
Burgers equation. We estimate the typical expansion time of the tubes
Reconstructing the two right-handed neutrino model
In this paper we propose a low-energy parametrization of the two right-handed
neutrino model, and discuss the prospects to determine experimentally these
parameters in supersymmetric scenarios. In addition, we present exact formulas
to reconstruct the high-energy leptonic superpotential in terms of the
low-energy observables. We also discuss limits of the three right-handed
neutrino model where this procedure applies.Comment: 28 pages, 4 figures. Typos corrected, references adde
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