Asymmetrical low-voltage ride through of brushless doubly fed induction generators for the wind power generation

Compared with the Doubly fed induction generators (DFIG), the brushless doubly fed induction generator (BDFIG) has a commercial potential for wind power generation due to its lower cost and higher reliability. In the most recent grid codes, wind generators are required to be capable of riding through low voltage faults. As a result of the negative sequence, induction generators response differently in asymmetrical voltage dips compared with the symmetrical dip. This paper gave a full behavior analysis of the BDFIG under different types of the asymmetrical fault and proposed a novel control strategy for the BDFIG to ride through asymmetrical low voltage dips without any extra hardware such as crowbars. The proposed control strategies are experimentally verified by a 250-kW BDFIG. © 2012 IEEE.

Impact of hydrated magnesium carbonate additives on the carbonation of reactive MgO cements

Reactive magnesia (MgO) cements have emerged as a potentially more sustainable and technically superior alternative to Portland cement due to their lower production temperature and ability to sequester significant quantities of CO2. Porous blocks containing MgO were found to achieve higher strength values than PC blocks. A number of variables are investigated to achieve maximum carbonation and associated high strengths. This paper focuses on the impact of four different hydrated magnesium carbonates (HMCs) as cement replacements of either 20 or 50%. Accelerated carbonation (20 C, 70-90% RH, 20% CO2) is compared with natural curing (20 C, 60-70% RH, ambient CO2). SEM, TG/DTA, XRD, and HCl acid digestion are utilized to provide a thorough understanding of the performance of MgO-cement porous blocks. The presence of HMCs resulted in the formation of larger size carbonation products with a different morphology than those in the control mix, leading to significantly enhanced carbonation and strength. © 2013 Elsevier Ltd.

Design trade-offs for energy regeneration and control in vehicle suspensions

This paper investigates the fundamental trade-offs involved in designing energy-regenerative suspensions, in particular, focusing on efficiency of power extraction and its effect on vehicle dynamics and control. It is shown that typical regenerative devices making use of linear-to-rotational elements can be modelled as a parallel arrangement of an inerter and a dissipative admittance. Taking account of typical adjustable parameters of the generator, it is shown, for a given suspension damping coefficient, that the power efficiency ratio scales with inertance. For a typical passenger vehicle, it is shown that there is a feasible compromise, namely that good efficiency is achievable with an inertance value that is not detrimental to vehicle performance. A prototype is designed and tested with a resistive termination and experimental results show good agreement between ideal and experimental admittances. The possibility to use dynamic (rather than purely resistive) loads to improve vehicle control without limiting the energy recovery is discussed. © 2013 Copyright Taylor and Francis Group, LLC.

Optimised IGBT turn-off under active voltage control in PEBB applications

Active Voltage Control (AVC) is an implementation of classic Proportional-Derivative (PD) control and multi-loop feedback control to force an IGBT to follow a pre-set switching trajectory. Previously, AVC was mainly used for controlling series-connected IGBTs in order to enable voltage balance between IGBTs. In this paper, the nonlinear IGBT turn-off transient is further discussed and the turnoff of a single IGBT under AVC is further optimised in order to meet the demand of Power Electronic Building Block (PEBB) applications. © 2013 IEEE.

Shaping pulse transitions by active voltage control for reduced EMI generation

High-performance power switching devices (IGBT/MOSFET) realise high-performance power converters. Unfortunately, with a high switching speed of the IGBT or MOSFET freewheel diode chopper cell, the circuit has intrinsic sources of high-level EMI. Therefore, costly EMI filters or shielding are normally demanded on the load and supply side. Although an S-shaped voltage transient with a high order of derivation eliminates the discontinuity and could suppress HF spectrum of EMI emissions, a practical control scheme is still under development. In this paper, Active Voltage Control (AVC) is applied to successfully define IGBT switching dynamics with a smoothed Gaussian waveform so a reduced EMI can be achieved without extra EMI suppression devices. © 2013 IEEE.

Control of material transport through pulse shape manipulation-a development toward designer pulses

The variety of laser systems available to industrial laser users is growing and the choice of the correct laser for a material target application is often based on an empirical assessment. Industrial master oscillator power amplifier systems with tuneable temporal pulse shapes have now entered the market, providing enormous pulse parameter flexibility in an already crowded parameter space. In this paper, an approach is developed to design interaction parameters based on observations of material responses. Energy and material transport mechanisms are studied using pulsed digital holography, post process analysis techniques and finite-difference modelling to understand the key response mechanisms for a variety of temporal pulse envelopes incident on a silicon (1/1/1) substrate. The temporal envelope is shown to be the primary control parameter of the source term that determines the subsequent material response and the resulting surface morphology. A double peak energy-bridged temporal pulse shape designed through direct application of holographic imaging data is shown to substantially improve surface quality. © 2014 IEEE.

Physical connection and disconnection control based on hot melt adhesives

Physical connection and disconnection control has practical meanings for robot applications. Compared to conventional connection mechanisms, bonding involving a thermal process could provide high connection strength, high repeatability, and power-free connection maintenance, etc. In terms of disconnection, an established bond can be easily weakened with a temperature rise of the material used to form the bond. Hot melt adhesives (HMAs) are such material that can form adhesive bonds with any solid surfaces through a thermally induced solidification process. This paper proposes a novel control method for automatic connection and disconnection based on HMAs. More specifically, mathematical models are first established to describe the flowing behavior of HMAs at higher temperatures, as well as the temperature-dependent strength of an established HMA bond. These models are then validated with a specific type of HMA in a minimalistic robot setup equipped with two mechatronic devices for automated material handling. The validated models are eventually used for determining open parameters in a feedback controller for the robot to perform a pick-and-place task. Through a series of trials with different wooden and aluminum parts, we evaluate the performance of the automatic connection and disconnection methods in terms of speed, energy consumption, and robustness. © 1996-2012 IEEE.

Design and control of a pendulum driven hopping robot

In this paper a new kind of hopping robot has been designed which uses inverse pendulum dynamics to induce bipedal hopping gaits. Its mechanical structure consists of a rigid inverted T-shape mounted on four compliant feet. An upright "T" structure is connected to this by a rotary joint. The horizontal beam of the upright "T" is connected to the vertical beam by a second rotary joint. Using this two degree of freedom mechanical structure, with simple reactive control, the robot is able to perform hopping, walking and running gaits. During walking, it is experimentally shown that the robot can move in a straight line, reverse direction and control its turning radius. The results show that such a simple but versatile robot displays stable locomotion and can be viable for practical applications on uneven terrain.

Highly efficient photoluminescence of Er2SiO5 films grown by reactive magnetron sputtering method

E2SiO5 thin films were fabricated on Si substrate by reactive magnetron sputtering method with subsequent annealing treatment. The morphology properties of as-deposited films have been studied by scanning electron microscope. The fraction of erbium is estimated to be 23.5 at% based on Rutherford backscattering measurement in as-deposited Er-Si-O film. X-ray diffraction measurement revealed that Er2SiO5 crystalline structure was formed as sample treated at 1100 degrees C for 1 h in O-2 atmosphere. Through proper thermal treatment, the 1.53 mu m Er3+-related emission intensity can be enhanced by a factor of 50 with respect to the sample annealed at 800 degrees C. Analysis of pump-power dependence of Er3+ PL intensity indicated that the upconversion phenomenon could be neglected even under a high photon flux of 10(21) (photons/cm(2)/sec). Temperature-dependent photoluminescence (PL) of Er2SiO5 was studied and showed a weak thermal quenching factor of 2. Highly efficienct photoluminescence of Er2SiO5 films has been demonstrated with Er3+ concentration of 10(22)/cm(3), and it opens a promising way towards future Si-based light source for Si photonics. (C) 2009 Elsevier B.V. All rights reserved.

An ultra-low power CMOS random number generator

This paper proposes an ultra-low power CMOS random number generator (RING), which is based on an oscillator-sampling architecture. The noisy oscillator consists of a dual-drain MOS transistor, a noise generator and a voltage control oscillator. The dual-drain MOS transistor can bring extra-noise to the drain current or the output voltage so that the jitter of the oscillator is much larger than the normal oscillator. The frequency division ratio of the high-frequency sampling oscillator and the noisy oscillator is small. The RNG has been fabricated in a 0.35 mu m CMOS process. It can produce good quality bit streams without any post-processing. The bit rate of this RNG could be as high as 100 kbps. It has a typical ultra-low power dissipation of 0.91 mu W. This novel circuit is a promising unit for low power system and communication applications. (c) 2007 Elsevier Ltd. All rights reserved.

Application of sampled grating to control the lasing wavelength in complex-coupled DFB laser

This paper reports that the complex-coupled distributed feedback laser with the sampled grating has been designed and fabricated. The +1st order reflection of the sampled grating is utilized for laser single mode operation, which is 1.5387 mu m in the experiment. The typical threshold current of the device is 30 mA, and the optical output power is about 10 mW at the injection current of 100 mA.

A power-saving scheme for IEEE 802.11 Ad hoc networks

In the Wireless Local Area Networks (WLANs), the terminals are often powered by battery, so the power-saving performance of the wireless network card is a very important issue. For IEEE 802.11 Ad hoc networks, a power-saving scheme is presented in Medium Access Control (MAC) layer to reduce the power consumption by allowing the nodes enter into the sleep mode, but the scheme is based on Time-Drive Scheme (TDS) whose power-saving efficiency becomes lower and lower with the network load increasing. This paper presented a novel energy-saving mechanism, called as Hybrid-Drive Scheme (HDS), which introduces into a Message.-Drive Scheme (MDS) and combines MDS with the conventional TDS. The MDS, could obtain high efficiency when the load is heavy; meanwhile the TDS has high efficiency when the network load is small. The analysis shows that the proposed HDS could obtain high energy-efficiency whether the network load is light or heavy and have higher energy-saving efficiency than conventional scheme in the IEEE 802.11 standard.

Formal specification and refinement of a safe train control function

Motivated by the design and development challenges of the BART case study, an approach for developing and analyzing a formal model for reactive systems is presented. The approach makes use of a domain specific language for specifying control algorithms able to satisfy competing properties such as safety and optimality. The domain language, called SPC, offers several key abstractions such as the state, the profile, and the constraint to facilitate problem specification. Using a high-level program transformation system such as HATS being developed at the University of Nebraska at Omaha, specifications in this modelling language can be transformed to ML code. The resulting executable specification can be further refined by applying generic transformations to the abstractions provided by the domain language. Problem dependent transformations utilizing the domain specific knowledge and properties may also be applied. The result is a significantly more efficient implementation which can be used for simulation and gaining deeper insight into design decisions and various control policies. The correctness of transformations can be established using a rewrite-rule based induction theorem prover Rewrite Rule Laboratory developed at the University of New Mexico.

Low power design in 100 MHz embedded SRAM

Low power design method is used in a 100MHz embedded SRAM. The embedded SRAM used in a FFT chip is divided into 16 blocks. Two-level decoders are used and only one block can be selected at one time by tristate control circuits, while other blocks are set stand-by. The SRAM cell has been optimized and the cell area has been minimized at the same time.