A discretized proportional base driver for Silicon Carbide Bipolar Junction Transistors

Silicon Carbide Bipolar Junction Transistors require a continuous base current in the on-state. This base current is usually made constant and is corresponding to the maximum collector current and maximum junction temperature that is foreseen in a certain application. In this paper, a discretized proportional base driver is proposed which will reduce, for the right application, the steady-state power consumption of the base driver. The operation of the proposed base driver has been verified experimentally, driving a 1200V/40A SiC BJT in a DC-DC boost converter. In order to determine the potential reduction of the power consumption of the base driver, a case with a dc-dc converter in an ideal electric vehicle driving the new European drive cycle has been investigated. It is found that the steady-state power consumption of the base driver can be reduced by approximately 63 %. The total reduction of the driver consumption is 2816 J during the drive cycle, which is slightly more than the total on-state losses for the SiC BJTs used in the converter. © 2013 IEEE.

Multi-objective optimisation of horizontal axis wind turbine structure and energy production using aerofoil and blade properties as design variables

The design of wind turbine blades is a true multi-objective engineering task. The aerodynamic effectiveness of the turbine needs to be balanced with the system loads introduced by the rotor. Moreover the problem is not dependent on a single geometric property, but besides other parameters on a combination of aerofoil family and various blade functions. The aim of this paper is therefore to present a tool which can help designers to get a deeper insight into the complexity of the design space and to find a blade design which is likely to have a low cost of energy. For the research we use a Computational Blade Optimisation and Load Deflation Tool (CoBOLDT) to investigate the three extreme point designs obtained from a multi-objective optimisation of turbine thrust, annual energy production as well as mass for a horizontal axis wind turbine blade. The optimisation algorithm utilised is based on Multi-Objective Tabu Search which constitutes the core of CoBOLDT. The methodology is capable to parametrise the spanning aerofoils with two-dimensional Free Form Deformation and blade functions with two tangentially connected cubic splines. After geometry generation we use a panel code to create aerofoil polars and a stationary Blade Element Momentum code to evaluate turbine performance. Finally, the obtained loads are fed into a structural layout module to estimate the mass and stiffness of the current blade by means of a fully stressed design. For the presented test case we chose post optimisation analysis with parallel coordinates to reveal geometrical features of the extreme point designs and to select a compromise design from the Pareto set. The research revealed that a blade with a feasible laminate layout can be obtained, that can increase the energy capture and lower steady state systems loads. The reduced aerofoil camber and an increased L/. D-ratio could be identified as the main drivers. This statement could not be made with other tools of the research community before. © 2013 Elsevier Ltd.

Design and testing of a medium-speed 250 kW Brushless DFIG

This paper presents the design and testing of a 250 kW medium-speed Brushless Doubly-Fed Generator (Brushless DFIG), and its associated power electronics and control systems. The experimental tests confirm the design, and show the system's steady-state and dynamic performance. The medium-speed Brushless DFIG in combination with a simplified twostage gearbox promises a low-cost low-maintenance and reliable drive train for wind turbine applications.

Designing output-feedback predictive controllers by reverse-engineering existing LTI controllers

An approach to designing a constrained output-feedback predictive controller that has the same small-signal properties as a pre-existing output-feedback linear time invariant controller is proposed. Systematic guidelines are proposed to select an appropriate (non-unique) realization of the resulting state observer. A method is proposed to transform a class of offset-free reference tracking controllers into the combination of an observer, steady-state target calculator and predictive controller. The procedure is demonstrated with a numerical example. © 2013 IEEE.

Performance analysis and testing of a 250 kW medium-speed brushless doubly-fed induction generator

This study presents the performance analysis and testing of a 250 kW medium-speed brushless doubly-fed induction generator (DFIG), and its associated power electronics and control systems. The experimental tests confirm the design, and showthe system's steady-state and dynamic performance and grid low-voltage ride- through capability. The medium-speed brushless DFIG in combination with a simplified two-stage gearbox promises a low-cost low-maintenance and reliable drivetrain for wind turbine applications. © The Institution of Engineering and Technology 2013.

Climb-enabled discrete dislocation plasticity

A small strain two-dimensional discrete dislocation plasticity framework coupled to vacancy diffusion is developed wherein the motion of edge dislocations is by a combination of glide and climb. The dislocations are modelled as line defects in a linear elastic medium and the mechanical boundary value problem is solved by the superposition of the infinite medium elastic fields of the dislocations and a complimentary non-singular solution that enforces the boundary conditions. Similarly, the climbing dislocations are modelled as line sources/sinks of vacancies and the vacancy diffusion boundary value problem is also solved by a superposition of the fields of the line sources/sinks in an infinite medium and a complementary non-singular solution that enforces the boundary conditions. The vacancy concentration field along with the stress field provides the climb rate of the dislocations. Other short-range interactions of the dislocations are incorporated via a set of constitutive rules. We first employ this formulation to investigate the climb of a single edge dislocation in an infinite medium and illustrate the existence of diffusion-limited and sink-limited climb regimes. Next, results are presented for the pure bending and uniaxial tension of single crystals oriented for single slip. These calculations show that plasticity size effects are reduced when dislocation climb is permitted. Finally, we contrast predictions of this coupled framework with an ad hoc model in which dislocation climb is modelled by a drag-type relation based on a quasi steady-state solution. © 2013 Elsevier Ltd. All rights reserved.

A novel modeling approach for design studies of brushless doubly fed induction generator based on magnetic equivalent circuit

Brushless doubly fed induction generator (BDFIG) has substantial benefits, which make it an attractive alternative as a wind turbine generator. However, it suffers from lower efficiency and larger dimensions in comparison to DFIG. Hence, optimizing the BDFIG structure is necessary for enhancing its situation commercially. In previous studies, a simple model has been used in BDFIG design procedure that is insufficiently accurate. Furthermore, magnetic saturation and iron loss are not considered because of difficulties in determination of flux density distributions. The aim of this paper is to establish an accurate yet computationally fast model suitable for BDFIG design studies. The proposed approach combines three equivalent circuits including electric, magnetic and thermal models. Utilizing electric equivalent circuit makes it possible to apply static form of magnetic equivalent circuit, because the elapsed time to reach steady-state results in the dynamic form is too long for using in population-based design studies. The operating characteristics, which are necessary for evaluating the objective function and constraints values of the optimization problem, can be calculated using the presented approach considering iron loss, saturation, and geometrical details. The simulation results of a D-180 prototype BDFIG are compared with measured data in order to validate the developed model. © 1986-2012 IEEE.

Transient ventilation dynamics induced by heat sources of unequal strength

We examine theoretically the transient displacement flow and density stratification that develops within a ventilated box after two localized floor-level heat sources of unequal strengths are activated. The heat input is represented by two non-interacting turbulent axisymmetric plumes of constant buoyancy fluxes B1 and B2 > B1. The box connects to an unbounded quiescent external environment of uniform density via openings at the top and base. A theoretical model is developed to predict the time evolution of the dimensionless depths λj and mean buoyancies δj of the 'intermediate' (j = 1) and 'top' (j = 2) layers leading to steady state. The flow behaviour is classified in terms of a stratification parameter S, a dimensionless measure of the relative forcing strengths of the two buoyant layers that drive the flow. We find that dδ1/dτ α 1/λ1 and dδ2/dτ α 1/λ2, where τ is a dimensionless time. When S 1, the intermediate layer is shallow (small λ1), whereas the top layer is relatively deep (large λ2) and, in this limit, δ1 and δ2 evolve on two characteristically different time scales. This produces a time lag and gives rise to a 'thermal overshoot', during which δ1 exceeds its steady value and attains a maximum during the transients; a flow feature we refer to, in the context of a ventilated room, as 'localized overheating'. For a given source strength ratio ψ = B1/B2, we show that thermal overshoots are realized for dimensionless opening areas A < Aoh and are strongly dependent on the time history of the flow. We establish the region of {A, ψ} space where rapid development of δ1 results in δ1 > δ2, giving rise to a bulk overturning of the buoyant layers. Finally, some implications of these results, specifically to the ventilation of a room, are discussed. © Cambridge University Press 2013.

Nanoengineering coaxial carbon nanotube-dual-polymer heterostructures.

We describe studies of new nanostructured materials consisting of carbon nanotubes wrapped in sequential coatings of two different semiconducting polymers, namely, poly(3-hexylthiophene) (P3HT) and poly(9,9'-dioctylfluorene-co-benzothiadiazole) (F8BT). Using absorption spectroscopy and steady-state and ultrafast photoluminescence measurements, we demonstrate the role of the different layer structures in controlling energy levels and charge transfer in both solution and film samples. By varying the simple solution processing steps, we can control the ordering and proportions of the wrapping polymers in the solid state. The resulting novel coaxial structures open up a variety of new applications for nanotube blends and are particularly promising for implementation into organic photovoltaic devices. The carbon nanotube template can also be used to optimize both the electronic properties and morphology of polymer composites in a much more controlled fashion than achieved previously, offering a route to producing a new generation of polymer nanostructures.

Direct temperature mapping of nanoscale plasmonic devices.

Side by side with the great advantages of plasmonics in nanoscale light confinement, the inevitable ohmic loss results in significant joule heating in plasmonic devices. Therefore, understanding optical-induced heat generation and heat transport in integrated on-chip plasmonic devices is of major importance. Specifically, there is a need for in situ visualization of electromagnetic induced thermal energy distribution with high spatial resolution. This paper studies the heat distribution in silicon plasmonic nanotips. Light is coupled to the plasmonic nanotips from a silicon nanowaveguide that is integrated with the tip on chip. Heat is generated by light absorption in the metal surrounding the silicon nanotip. The steady-state thermal distribution is studied numerically and measured experimentally using the approach of scanning thermal microscopy. It is shown that following the nanoscale heat generation by a 10 mW light source within a silicon photonic waveguide the temperature in the region of the nanotip is increased by ∼ 15 °C compared with the ambient temperature. Furthermore, we also perform a numerical study of the dynamics of the heat transport. Given the nanoscale dimensions of the structure, significant heating is expected to occur within the time frame of picoseconds. The capability of measuring temperature distribution of plasmonic structures at the nanoscale is shown to be a powerful tool and may be used in future applications related to thermal plasmonic applications such as control heating of liquids, thermal photovoltaic, nanochemistry, medicine, heat-assisted magnetic memories, and nanolithography.

Network reconstruction using knock-out and over-expression data

This paper outlines necessary and sufficient conditions for network reconstruction of linear, time-invariant systems using data from either knock-out or over-expression experiments. These structural system perturbations, which are common in biological experiments, can be formulated as unknown system inputs, allowing the network topology and dynamics to be found. We assume that only partial state measurements are available and propose an algorithm that can reconstruct the network at the level of the measured states using either time-series or steady-state data. A simulated example illustrates how the algorithm successfully reconstructs a network from data. © 2013 EUCA.

Twin plane re-entrant mechanism for catalytic nanowire growth.

A twin-plane based nanowire growth mechanism is established using Au catalyzed Ge nanowire growth as a model system. Video-rate lattice-resolved environmental transmission electron microscopy shows a convex, V-shaped liquid catalyst-nanowire growth interface for a ⟨112⟩ growth direction that is composed of two Ge {111} planes that meet at a twin boundary. Unlike bulk crystals, the nanowire geometry allows steady-state growth with a single twin boundary at the nanowire center. We suggest that the nucleation barrier at the twin-plane re-entrant groove is effectively reduced by the line energy, and hence the twin acts as a preferential nucleation site that dictates the lateral step flow cycle which constitutes nanowire growth.

Reference frame re-alignment for vector control of the brushless doubly-fed machine

Vector control provides stability and performance when applied to the brushless doubly-fed machine, however cross-coupling effects can arise between inputs and outputs. To address these effects, a procedure is proposed to both visualize and minimize the cross-coupling by means of steady-state mapping and a re-alignment of the dq reference frame. With this method implemented, gain-response tests show improved decoupling across the operating region. © 2013 EUCA.

A study of converter rating for brushless DFIG wind turbines

This paper studies the converter rating requirement of a Brushless Doubly-Fed Induction Generator for wind turbine applications by considering practical constraints such as generator torque-speed requirement, reactive power management and grid low-voltage ride-through (LVRT). Practical data have been used to obtain a realistic system model of a Brushless DFIG wind turbine using steady-state and dynamic models. A converter rating optimization is performed based on the given constraints. The converter current and voltage requirements are examined and the resulting inverter rating is compared to optimization algorithm results. In addition, the effects of rotor leakage inductance on LVRT performance and hence converter rating is investigated.

A discretized proportional base driver for silicon carbide bipolar junction transistors

Silicon carbide (SiC) bipolar junction transistors (BJTs) require a continuous base current in the on-state. This base current is usually made constant and is corresponding to the maximum collector current and maximum junction temperature that is foreseen in a certain application. In this paper, a discretized proportional base driver is proposed which will reduce, for the right application, the steady-state power consumption of the base driver. The operation of the proposed base driver has been verified experimentally, driving a 1200-V/40-A SiC BJT in a dc-dc boost converter. In order to determine the potential reduction of the power consumption of the base driver, a case with a dc-dc converter in an ideal electric vehicle driving the new European drive cycle has been investigated. It is found that the steady-state power consumption of the base driver can be reduced by approximately 60%. The total reduction of the driver consumption is 3459 J during the drive cycle, which is slightly more than the total on-state losses for the SiC BJTs used in the converter. © 2013 IEEE.