Simulation on modified hysteresis current control in half-bridge bidirectional DC-DC converter

This paper proposes a modified hysteresis current control method for half bridge bidirectional DC-DC converter (HBDC). Hysteresis current controller is modified by adding logic circuit at input signal S1 and S2 to change performance of inductor current, IL. According to current direction transition, IL stays at zero in a moment. It is happens when Irefp is crossing zero and continues bouncing when Irefm is crossing zero. This method is applied to reduce loss in HBDC performance, which as a result will achieve reduction in switching losses and conduction losses. The conduction losses and switching losses has been analyzed which conduction losses has slight changes in losses reduction and switching losses is reduce from 6.31 J to 4.53 J. The proposed hysteresis current controller was simulated using PSIM and the losses is verify on each switching changes. The result validated proposed hysteresis current control capability in losses reduction

ACTIVE FILTERING APPLIED TO A LINE-COMMUTATED INVERTER FED PERMANENT MAGNET WIND GENERATOR

In this paper, the implementation of a shunt active power filter (APF) for compensating reactive and harmonic currents generated by a line-commutated inverter (LCI) in the permanent magnet synchronous generator (PMSG) wind energy conversion systems (WECS) is presented. The system consists of wind turbine and PMSG with a sensor-less MPPT and a LCI to deliver the power to the grid. The filter consists of a three-phase current controlled voltage source inverter (CC-VSI) with a filter inductance at the ac output and a dc-bus capacitor. The CC-VSI is operated to directly control the ac grid current to be sinusoidal and in phase with the grid voltage. The switching is controlled using ramptime current control, which is based on the concept of zero average current error. The simulation results indicate that the filter is able to handle the reactive and harmonic currents, so that the grid currents are sinusoidal, in phase with the grid voltages and symmetrical. The filter also can operate accurately regarding the wind variation

Evaluation of Traumatic Brain Injury Using Magnetic Resonance Spectroscopy

Traumatic brain injury (TBI) is responsible for a third of all injury-related deaths in the United States. With the lack of structural imaging biomarkers available for the detection and evaluation of TBI sequelae, unambiguous diagnosis and prognosis in TBI still remain a huge challenge. Furthermore, complications arising from TBI can lead to cognitive, social, emotional and behavioral defects later in life. Even in confirmed cases of head injury, computed tomography (CT) and conventional MR techniques are limited in their ability to predict the neuropsychological outcome of patients. While the initial trauma can induce structural impairment of brain tissue, the bulk of the cerebral dysfunction ensuing from TBI is due to alterations in cellular biochemical processes that occur in the days and weeks following the traumatic incident. There is therefore a need for advanced imaging modalities that are able to probe the more underlying cellular changes that are induced by TBI. Understanding such cellular changes will be useful in predicting patient outcome and designing interventions to alleviate the injury sequelae. Magnetic Resonance Spectroscopy (MRS) is a non-invasive imaging modality that is capable of detecting cellular metabolic changes in in vivo tissue. In this study we will assess the use of MRS as a clinically relevant tool in the diagnostic and prognostic evaluation of TBI. To this end, we have laid out the following specific aims: (i) To understand the nature and implications of neurometabolic sequelae in mild traumatic brain injury (mTBI) by carrying out cross-sectional comparisons of mTBI patients to neurologically healthy subjects at different stages of injury and to determine associations between early neurometabolic patterns and chronic neuropsychological performance in mTBI patients (ii) To develop novel MRS pulse sequence acquisition and data processing techniques that will enable a more thorough neurometabolic evaluation of TBI and enhance quantification of MRS data (iii) To develop automated classification systems in mTBI using early neurometabolic information that will aid discrimination between subjects with and without injury related sequelae and allow the prediction of symptomatic outcome at the later stages of injury. The research presented herein will help to enhance the utility of MRS in the evaluation of TBI

Effect of sintering parameters on the mechanical and physical properties of sinter formed materials

Sinter formed materials have been studied in this project. The powders used were stainless steel powders and zinc oxide powders. Three stainless steel powders were studied to evaluate the compressibility, shrinkage and densification during sintering and strength behaviour. The effect of sintering temperature on the high strain rate behaviour of stainless steel powder compacts has been investigated. A dynamic constitutive equation, which describes the material behaviour under dynamic loading, has been established. This equation takes into account the density of the compact. Regarding ceramic powders, the compressibility of four zinc oxide varistor powders have been studied taking into account the particle size, binder content, binder type and lubricant. The green and sintered strength of ceramic compacts have been assessed in relation to the above mentioned parameters. As for sintering, it was required to optimize the temperature profile of the sintering process. To accomplish this, two instruments were developed. The first one was used to monitor and control the weight loss, due to the binder burn out, at a constant rate. The second instrument was developed to monitor and control the shrinkage during sintering. The optimized temperature profile during binder burn out was checked for verification and it has proved reliable. A brief look at the grain growth during sintering was carried out to see the effect of heating rate and soaking time on the grain growth since this is a critical material property influencing the electrical characteristics of zinc oxide varistors

Dynamics of the Inertia Coupled Rimless Wheel with Frictional Losses and Actuation

The Inertia Coupled Rimless (ICR) wheel is a mechanically simple walking device capable of energy efficient motion. Typically, walking robots that are capable of level ground transport are extremely energy inefficient. To address this performance issue, the ICR wheel was examined while considering real-world frictional losses. The ICR wheel has been previously shown to be capable of collisionless, periodic motion, but until now, the ICR wheel had only been examined as an ideal, theoretical model. The inertia device within the system was tested to determine both the magnitude of energy loss due to damping and a suitable model for its motion. Fitting friction models to the experimental results showed that the a visciously damped model most accurately represented the system\u27s motion. Simulations revealed that the ICR wheel with friction would be capable of walking passively on a ramp with half stable, periodic walking, but the collisionless motion was lost. An actuation scheme was designed in simulation to allow an ICR wheel with damping to achieve collisionless motion on level ground. Experimental testing of a passive ICR wheel on a $3^o$ ramp showed that a cost of transport of at least 0.052 is possible with this system. Simulations suggest that, with the inclusion of an actuation scheme, the cost of transport for the same system on level ground could be as low as 0.024. Understanding how to overcome frictional losses lays the foundation for the creation of a walking robot capable of level ground transport with significantly less energy use than current models are capable of achieving

A study of impact breakage of single rock specimen using discrete element method

Comminution is a critical stage of mineral processing which aims to reduce the size of ore particles through breakage, consequently increasing the likelihood of the liberation of valuable minerals. However, comminution is highly energy-intensive and an understanding of the key breakage mechanisms has been identified as an important factor in improving the efficiency of the process. Several factors, such as pre-existing cracks, mineralogical composition, ore shape and size are known to affect ore breakage behaviour during breakage. To investigate breakage mechanisms, it is important to be able to determine how individual factor influences the breakage behaviour of rock specimens. However, isolating and investigating individual factors under experimental conditions is challenging and typically impractical. Numerical techniques such as the Bonded Particle Model-Discrete Element Method (BPMDEM) have been developed as a means of investigating in isolation, the effects of different factors on ore breakage behaviour under closely controlled breakage conditions using synthetic rock specimens. This study investigates how individual factors influence rock specimen breakage using BPM-DEM numerical methods. Numerical simulations were conducted using ESyS-particle 2.3.5, an open-source discrete element method (DEM) software package which uses Python-based libraries to generate geometries and simulations and a C++ engine for mathematical computations. Empirical calibration relationships were developed to relate microstructural model parameters to the macroscopic mechanical properties that are typically obtained from standard geotechnical breakage experiments. The robustness of the model was evaluated by considering the sensitivity of fracture measures to the variation of model resolution, size-dependency and macroscopic mechanical properties (Young's modulus and uniaxial compressive strength) of the numerical specimens. A comparative study of single rock specimen breakage using the current BPM-DEM and laboratory SILC experiments carried out by Barbosa et al. (2019) was conducted. The measured fracture force and fracture patterns at different sizes for both cylindrical and spherical synthetic rock specimens were examined. Furthermore, the model was used to study, in isolation, the influence of pre-existing cracks in rock specimens and differing mineralogical compositions upon measurable breakage properties. Numerical rock specimens with pre-existing cracks were constructed using a microcrack approach, while a unique approach with the insertion of "seed points" was developed and demonstrated to construct numerical rock specimens with varying mineralogical compositions. Results from the numerical simulations showed that a high model resolution with a sufficiently large number of DEM-spheres exhibited results with the least deviation and error with respect to fracture measures, and, was therefore considered numerically stable. The dependency of fracture measurements on specimen size showed an expected increase in the measured fracture force as the specimen size increases. The variation of the macroscopic Young's modulus and uniaxial compressive strength against the fracture measures emphasised that the locus of these mechanical properties against the fracture measure can be used to specify a calibration relationship. Results of the comparative study showed that for both cylindrical and spherical rock specimens, the DEM consistently predicted the fragment patterns as well as the increase in the measured fracture force as the specimen size increased. The investigation on the effect of pre-existing cracks revealed that an increasing number of pre-existing cracks in rock specimens necessitated lower fracture force and consequently produced a low amount of new fracture surface area. For the binary phase mineralogical composition in the study, it was found that the fracture force decreased with an increase in the concentration of the softer component due to the increased percentage of weakness in the specimen. It was concluded that, with an appropriate calibration exercise and a realistic specification of material properties from the evaluation study, the DEM as a tool was sufficient to act as a "virtual laboratory" to isolate and study the individual effects of factors that influence ore breakage. The understanding of these results highlighted two important points. Firstly, this study was able to unravel some of the possible causes of the inefficiency in comminution practices, whereby significant amounts of energy can be expended to achieve minimal gains in respect of enhancing liberation due to pre-weakening and mineralogical composition. Secondly, it emphasised some of the causes of the variation observed during ore characterisation on a laboratory breakage device, attributable to pre-weakening and mineralogical composition

Design And Characterization Of Noveldevices For New Generation Of Electrostaticdischarge (esd) Protection Structures

The technology evolution and complexity of new circuit applications involve emerging reliability problems and even more sensitivity of integrated circuits (ICs) to electrostatic discharge (ESD)-induced damage. Regardless of the aggressive evolution in downscaling and subsequent improvement in applications\u27 performance, ICs still should comply with minimum standards of ESD robustness in order to be commercially viable. Although the topic of ESD has received attention industry-wide, the design of robust protection structures and circuits remains challenging because ESD failure mechanisms continue to become more acute and design windows less flexible. The sensitivity of smaller devices, along with a limited understanding of the ESD phenomena and the resulting empirical approach to solving the problem have yielded time consuming, costly and unpredictable design procedures. As turnaround design cycles in new technologies continue to decrease, the traditional trial-and-error design strategy is no longer acceptable, and better analysis capabilities and a systematic design approach are essential to accomplish the increasingly difficult task of adequate ESD protection-circuit design. This dissertation presents a comprehensive design methodology for implementing custom on-chip ESD protection structures in different commercial technologies. First, the ESD topic in the semiconductor industry is revised, as well as ESD standards and commonly used schemes to provide ESD protection in ICs. The general ESD protection approaches are illustrated and discussed using different types of protection components and the concept of the ESD design window. The problem of implementing and assessing ESD protection structures is addressed next, starting from the general discussion of two design methods. The first ESD design method follows an experimental approach, in which design requirements are obtained via fabrication, testing and failure analysis. The second method consists of the technology computer aided design (TCAD)-assisted ESD protection design. This method incorporates numerical simulations in different stages of the ESD design process, and thus results in a more predictable and systematic ESD development strategy. Physical models considered in the device simulation are discussed and subsequently utilized in different ESD designs along this study. The implementation of new custom ESD protection devices and a further integration strategy based on the concept of the high-holding, low-voltage-trigger, silicon controlled rectifier (SCR) (HH-LVTSCR) is demonstrated for implementing ESD solutions in commercial low-voltage digital and mixed-signal applications developed using complementary metal oxide semiconductor (CMOS) and bipolar CMOS (BiCMOS) technologies. This ESD protection concept proposed in this study is also successfully incorporated for implementing a tailored ESD protection solution for an emerging CMOS-based embedded MicroElectroMechanical (MEMS) sensor system-on-a-chip (SoC) technology. Circuit applications that are required to operate at relatively large input/output (I/O) voltage, above/below the VDD/VSS core circuit power supply, introduce further complications in the development and integration of ESD protection solutions. In these applications, the I/O operating voltage can extend over one order of magnitude larger than the safe operating voltage established in advanced technologies, while the IC is also required to comply with stringent ESD robustness requirements. A practical TCAD methodology based on a process- and device- simulation is demonstrated for assessment of the device physics, and subsequent design and implementation of custom P1N1-P2N2 and coupled P1N1-P2N2//N2P3-N3P1 silicon controlled rectifier (SCR)-type devices for ESD protection in different circuit applications, including those applications operating at I/O voltage considerably above/below the VDD/VSS. Results from the TCAD simulations are compared with measurements and used for developing technology- and circuit-adapted protection structures, capable of blocking large voltages and providing versatile dual-polarity symmetric/asymmetric S-type current-voltage characteristics for high ESD protection. The design guidelines introduced in this dissertation are used to optimize and extend the ESD protection capability in existing CMOS/BiCMOS technologies, by implementing smaller and more robust single- or dual-polarity ESD protection structures within the flexibility provided in the specific fabrication process. The ESD design methodologies and characteristics of the developed protection devices are demonstrated via ESD measurements obtained from fabricated stand-alone devices and on-chip ESD protections. The superior ESD protection performance of the devices developed in this study is also successfully verified in IC applications where the standard ESD protection approaches are not suitable to meet the stringent area constraint and performance requirement

PWM motor control: Model and servo analysis

In recent years, the performance requirements of high power servo motor systems utilizing pulse width modulated (PWM) switching amplifiers have steadily increased. These PWM motor amplifiers perform an important function in the d.c. servo system by boosting the low level command signal to the high voltage and current levels required by the motor. Ideally, this power gain is to be constant over all input frequencies but, in reality, gain is frequency dependent which affects system dynamics. The amplifier gain and phase versus frequency relationships an*i amplifier noise and d.c. offsets which may affect system response must be known to the servo designer to properly design the motor control system. The switching effects of the PWM amplifier may result in making the overall system unstable if the system bandwidth is kept high with respect to the PWM switching frequency. Since the standard servo design techniques utilize linear system modeling, analysis, and compensation, it would be very advantageous to the design engineer to have a linear model which best approximates the true nonlinear PWM amplifier. This work will look at the output response of the PWM amplifier with respect to stability and output ripple. A linear model will be developed which simulates these stability and ripple effects in a position control servo system and which is valid as system bandwidth reaches one-third the PWM switching frequency. This work extends the application of the Principle of Equivalent Areas [141 to the bipolar PWM amplifier. It is then combined with a detailed analysis of the PWM waveform by Double Fourier Transform to yield the unique PWM switching effects in a position control servo system. Theoretical results of the newly derived sampling plus harmonic linear model are verified by computer simulation