Bidirectional AC-DC Converter for Vehicle-to-Grid (V2G) Applications

Electric vehicles are growing at a rapid pace in the internal combustion engine dominated transportation sector, and bring environmental and economic benefits to society. Electric vehicles produce nearly zero carbon emission, provided that they are charged through renewable energy sources. Electric vehicles reduce our dependency on foreign oil and also offer additional benefits like Vehicle-to-grid (V2G). V2G is a technology that allows electric energy stored in the electric vehicle batteries to be returned to the grid during peak demand. V2G can also provide voltage regulation, voltage shaving, reactive power compensation and distributed generation. This necessitates that an electric vehicle battery charger be bi-directional, capable of sinking or sourcing real and reactive power. The state of the art battery charging converter is unidirectional and has multiple stages of power conversion. In this thesis, a single phase, single stage, isolated, bi-directional Silicon Carbide (SiC) AC-DC converter based on Dual Active Bridge (DAB) topology is proposed and analyzed. Direct-quadrature axis (DQ) current control of the DABbased topology is implemented with phase shift modulation. Simulation results are presented with various operating conditions showing the converter’s ability to sink or source real and reactive power in the AC grid. Hardware and firmware implementation of a single phase bi-directional AC-DC converter operating at 100 kHz utilizing Silicon Carbide (SiC) MOSFETs are discussed in detail. Experimental results are shown confirming simulation results. A single phase bi-directional AC-DC converter uses large electrolytic capacitors to filter ripple currents in the DC bus. Electrolytic capacitors are bulky and are prone to failure. These electrolytic capacitors can be eliminated by rejecting the ripple current in the DC bus. The ripple current is rejected by injecting a current of same magnitude and opposite phase to the ripple current. A rigorous analysis is performed on the ripple rejection technique used in single phase bi-directional AC-DC converters. Simulation results are presented to verify the analysis. A three phase bi-directional AC-DC converter improves the charging time of the electric vehicles by charging the batteries at a higher power level. A three phase, single stage, isolated, bi-directional AC-DC converter is analyzed. DQ current control of the three phase AC-DC converter is implemented in simulation to verify the analysis

Investigation on the Effects of Fastening Parameters on the Handle Displacement of a Pistol Grip Tool

Workers in automotive assembly lines routinely use DC-powered pistol grip tools to install threaded fasteners. While these tools are easy to use and increase production quality, tool operators are subjected to impulsive reaction torques that produce forceful rotary displacement of the tool handle. While operators try to resist this reaction, forces exerted by the forearm muscles are often insufficient, thereby producing eccentric contractions. Repeated exposure to such forces is known to cause tendonitis, fatigue, and physical stress. The objective of this study was to investigate the operational parameters and optimize conditions that minimize the tool handle displacement. A deterministic approach was considered to identify the system parameters. The tool-operator system was mathematically represented using a single degree-of-freedom torsional model. An in-vivo study of 10 experienced workers was conducted to estimate the typical ranges of operator stiffness. Tightening tasks were performed at 3 torques (5, 7.5, 10 Nm), and 4 fastener locations that correspond to varying orientations of the wrist. The mean operator stiffness was found to be 1.11 kN/m. A pistol grip tool simulator was designed and developed to emulate the dynamics of tightening operation without the use of human operators. A slider-crank mechanism was considered to represent the kinematics of the torsional system, and a pneumatic actuator was used to represent individual operator stiffness. A parametric study observed the effects on tool handle response due to varying torque, operator stiffness, spindle speed, fastener material, drive style, and fastener head type. Results showed that an increase in applied torque (5–7.5 Nm) also increased the angular displacement of the tool handle (42.2°–58.5°). Variation in stiffness resulted in an inverse effect on the handle response. At 7.5 Nm, it was observed that wrist ulnar deviation produced the most handle displacement (59.2°), whereas wrist flexion produced the least (57.3°). Variation in the operational speed of tool spindle showed no significant effect on the handle displacement. Three fastener materials, alloy steel, stainless steel, and brass were tested. It was observed that alloy steel resulted in the least displacement (65.4°), whereas brass produced the most (85.7°). Between the two drive styles, it was observed that a Hex drive produced significantly higher response (69.9°) than a Torx Plus drive (63.4°). Button Head fasteners produced significantly higher response (76.2°) compared to Flat Head fasteners (66.9°). Based on this data, it was concluded that the designed pistol grip tool simulator can be used to investigate and optimize the operational parameters such as tool tightening algorithm, fastener types, and task locations, thus minimizing the tool handle displacement and mitigating forearm strain injuries

Fracture strength estimation of L3-L4 intervertebral disc using FEA

Mechanical stress and fracture analysis of the human lumbar intervertebral discs are important in assessing disorders related to lower back pain and ageing. Finite element modelling and simulation approaches assist in easier prediction of the disc behaviour under different load conditions. The causes of mechanical failure and morphological changes still remain partially speculative. The present study addresses the issue by developing a finite element model of an L3-L4 lumbar intervertebral disc subjected to different axial compressive loadings. The morphological deformations and stress concentration regions within the disc are analyzed and reported. A mathematical relation is established to estimate the breaking strength of an L3-L4 intervertebral disc, thus indicating the risk of disc failure based on the applied load

Mode based frequency behaviour of a cracked beam

Structural analysis is mainly concerned with predicting the behaviour of a structure when subjected to any external excitation. Dynamic analysis of simple structures can be carried out using finite element analysis on various computing platforms such as MatLab. In the case of industrial applications, dynamic analysis is mainly carried out using simulations on softwares such as Ansys. The present paper compares mathematical and simulation analysis of cracked beam and the dynamic behaviour with respect to mode shape and crack position is reported

Screening of Potential Plant Growth Promoting Properties of Bacillus Species Isolated from Different Regions of Nepal

The deleterious effects of intensive use of chemical fertilizers and pesticides in agriculture has led to the substantial research efforts on finding the alternatives to these agrochemicals. This study was aimed to isolate Bacillus species from soil of different regions of Nepal and screen for their ability to promote plant growth directly or indirectly by testing their ability to produce plant growth hormone indole acetic acid, hydrogen cyanide, ammonia and protease as well as phosphate solubilization. Thirty nine Bacillus strains were isolated from 25 soil samples of different regions of Kathmandu and Chitwan districts of Nepal. These isolates were tested for plant growth promoting traits in vitro. Among the total isolates, about 48.7% were indole acetic acid producers, 38.4% of the isolates showed the ability to solubilize the phosphate, 71.8% were able to produce ammonia and all the isolates had the ability to produce hydrogen cyanide and protease. The isolated strains showed positive results to maximum PGPR traits and exhibited a potential to be used as alternatives to chemical fertilizers and pesticides and could be used as low-cost bio-based technology to promote plant growth in the agricultural sector

Dynamics of osteoblasts during bone remodeling cycle

Bone is a dynamic connective tissue which adjusts to load variations through continuous bone remodeling, which occurs due to the dynamic behavior of bone cells. Many researchers made attempts in obtaining the dynamic characteristics of osteoblasts and its role in bone remodeling cycle. While making an effort to understand the effects of mechanical stimuli on the osteoblast, certain ambiguity is observed in the past literatures. This paper is to demonstrate the dynamics of osteoblast cells and exhibition of different natural frequencies during its life cycle. Osteoblast is modeled as a frustum of a sphere, considering it as a continuum model. The three prominent parts of an osteoblast, i.e., membrane, cytoplasm and nucleus are considered with reported material properties. Lifespan of an active osteoblast during bone remodeling cycle is considered as 90 days and progressive osteoblast stages are analysed using Ansys. First ten natural frequencies and mode shapes are extracted for nine stages and reported. It is observed that the natural frequencies of a micron sized osteoblast are in the range of kHz. A mathematical relation for the lifespan of an active osteoblast is obtained using curve fitting for fundamental natural frequencies. The natural frequency for exciting an active osteoblast on each particular day during its lifespan can be derived from the relation. This relation can serve as a guiding tool in bioengineering for in vitro bone cell culturing. Results also throw light on the excitation frequency and natural frequency of an osteoblast for proper analysis purpose. The different modes of vibration of osteoblast is identified and reported

Mathematical modelling for dynamic analysis of cracked L-shape beam

In this paper, a finite element mathematical model to evaluate natural frequencies and Frequency Response Functions (FRFs) of an L-shaped cracked beam structure is established. Dynamics of L-shaped beam structure is a very challenging subject and very little information is reported in literature. L-shaped beam structure is assumed to be fixed at end of the vertical column and free at the other end of the horizontal column. Natural frequencies are evaluated using finite element method in MatLab and simulations using Ansys (Version 18.2) is carried out to validate the mathematical model. Totally 18 cases with different crack positions and three different crack depths are considered for the analysis. Results obtained by both methods are tabulated and find a very good agreement in the results. Reported results can be used as a benchmark for further study of crack propagation and fatigue failure analysis in built-up structures

Phase Transitions and Magnetoresistance in Ni50Mn50−xInx Heusler Alloys

The phase transitions and magnetoresistance in polycrystalline ferromagnetic Ni50Mn50−xInx (15 ≤ x ≤ 16.2) Heusler alloys were studied through ac susceptibility, magnetization, thermal expansion, and resistivity measurements in the temperature interval of 5–400 K. The temperatures of the martensitic transformations were found to be strongly dependent on In concentration and on the strength of the applied external magnetic field. We observed large magnetoresistance (MR) Δρ/ρo ≈ −80% for x = 16 at T ≈ 125 K and Δρ/ρo ≈ −56% for x = 15 at T ≈ 309 K for ΔH = 5 T. In addition to large MR, the Ni50Mn50−xInx system exhibits ferromagnetic shape-memory effect and a large magnetic entropy change. Hence this system has potential to be a multifunctional applied material