SEPIC DC – AC Converter Design and Operation

poster abstractThis paper focuses on the design and study of operation of the SEPIC converter which is modified to function as an inverter i.e. converts DC input to AC output. The modified converter consists of reduced number of switches which increases the efficiency and also improves the quality of the waveforms generated. The conventional SEPIC converter consists of two inductors, two capacitors, one transistor switching at high frequency and a diode. The modified SEPIC replaces the diode with a polarity reversing switch component. This component contains two reverse connected transistors T1 and T2 which are synchronized with the polarity of the output waveform. This new inverter is capable of producing pure sinusoidal waveform with only three switches of which only one is switched at high frequency, Q. The new inverter is found to operate in four different modes of operation to produce positive and negative cycles of output voltage. The modes 1 and 2 of operation have the switches Q and T1 operating and produce positive peak and the modes 3 and 4 of operation have the switches Q and T2 operating and produce negative peak. The inductor connected in the input side of the inverter is chosen to be large enough to maintain continuous conduction. State Space Averaging technique is used to model the system where the currents through the inductors and voltages across the capacitors are considered to be the state variables. The state space representation of each mode of operation is obtained and the system is averaged over the positive peak and negative peak separately. The state space model of the inverter is validated using MATLAB/SIMULINK. The inverter model was simulated using SimPowerSystems tool box of MATLAB and found to produce pure sinusoidal waveform. The harmonics were found to be reduced to a great extent

Control of Single Switch Inverters

poster abstractThe single switch inverter was introduced to generate a pure sinusoidal output voltage. The system behaves like a non-minimum phase system in all operating ranges except when it is operating to produce negative half cycle in buck mode. When addressed from a control perspective, the right half plane zeros or the non-minimum phase zeros in the transfer function complicate the control design scheme. The Dual Feed-forward Predictive Control (DFPC) is a method of feed-forward control is used to force the non-minimum phase system to behave like a minimum phase system. The controller successfully isolates the non-minimum phase part of the system from the minimum phase. Both separated minimum phase and non-minimum phase sub-systems were used in the dual feed-forward scheme to generate desired references. The non-minimum phase dynamics are transformed to minimum phase by using an inverse system transfer function as parallel compensator. In this method, the plant is split into two parts to generate two signals. One signal is to make the plant track with a feed-forward control signal that drives the plant to track the reference signal. The signals produced by the feed-forward transfer functions are assumed to contain bounded energy and have no influence on the closed loop stability. For perfect tracking, the error should reach zero which can be accomplished using various types of controller including a simple gain. However, in the new inverter circuit, an adaptive PI controller is required to adjust the gains continuously

Solar Micro Inverter

Indiana University-Purdue University Indianapolis (IUPUI)The existing topologies of solar micro inverter use a number of stages before the DC input voltage can be converted to AC output voltage. These stages may contain one or more power converters. It may also contain a diode rectifier, transformer and filter. The number of active and passive components is very high. In this thesis, the design of a new solar micro inverter is proposed. This new micro inverter consists of a new single switch inverter which is obtained by modifying the already existing single ended primary inductor (SEPIC) DC-DC converter. This new inverter is capable of generating pure sinusoidal waveform from DC input voltage. The design and operation of the new inverter are studied in detail. This new inverter works with a controller to produce any kind of output waveform. The inverter is found to have four different modes of operation. The new inverter is modeled using state space averaging. The system is a fourth order system which is non-linear due to the inherent switching involved in the circuit. The system is linearized around an operating point to study the system as a linear system. The control to output transfer function of the inverter is found to be non-minimum phase. The transfer functions are studied using root locus. From the control perspective, the presence of right half zero makes the design of the controller structure complicated. The PV cell is modeled using the cell equations in MATLAB. A maximum power point tracking (MPPT) technique is implemented to make sure the output power of the PV cell is always maximum which allows full utilization of the power from the PV cell. The perturb and observe (P&O) algorithm is the simplest and is used here. The use of this new inverter eliminates the various stages involved in the conventional solar micro inverter. Simulation and experimental results carried out on the setup validate the proposed structure of inverter

Trauma from Occlusion: Practical Management Guidelines

Occlusal trauma is trauma to the periodontium from functional or parafunctional force’s causing damage to the teeth and its attachment apparatus by exceeding its adaptive and reparative capacities. Occlusal instability is a common cause for trauma from occlusion, resulting in numerous complications. It often leads to interference which reflexively shifts or slides the jaw forward on one or both the side to find a spot where most teeth come together. This action protects the teeth from injury caused by chewing on just one tooth. Overtime, this shift can cause a whole host of problems from TMJ pain, post restorative complications, headache, tooth sensitivity, recession, broken and loss of teeth and orofacial pain. These occlusal interferences and bite discrepancies are treatable with minimally invasive dentistry. Occlusal equilibration is a therapy that is used when the cause of trauma is due to occlusal instability. This involves the reshaping of the teeth where the improper biting surfaces are located. The key lies in decoding the cause, but often treatment is only directed towards the effects. Only a thorough evaluation and occlusal analysis will lead to a definitive diagnosis that will help in better anticipation of the damages

Traditional Indian way of eating – an overview

Eating (also known as consuming) is the ingestion of food, typically to provide a heterotrophic organism with energy and to allow for growth. Hands are most vital for cooking sustenance and for eating. Many individuals find eating with hands unhygienic, primitive, and nauseating; however, eating food with hands is associated with not just the body but also the psyche and soul. There is rationality behind the Indian routine of eating with fingers. Different types of vessels are used as needed to set up the sustenance . In Indian families, distinctive leaves such as banana leaf and jerk teak leaf are used for serving food. While eating in abundance, one must use hands to feel the food. Eating with a spoon or fork is often the current practice and is considered clean and advantageous; however, the vast majority of people do not understand that there is reasoning behind eating sustenance with hands. Eating by sitting on the floor has multitudinous advantages and is yet to be popularized in different regions across Asia. Keywords: Hands, Leaves, Meal on the floor, Vessels, Way of eatin

Digitized radiovisiographic analysis of dental pulp of permanent mandibular first molar and second premolar for age estimation using tooth coronal index method

Background: Teeth have become a valuable index to estimate age of an individual in forensic odontology. The advent of radiovisiography (RVG) has led to accurate calculation of dental age, which may be due to more precise RVG images than other radiographic techniques. Objectives: The study aimed at estimating the age of an individual from mandibular premolar and molar through tooth coronal index (TCI) measured from digital intraoral radiographic images (RVG). Materials and Methods: Using RVG 176 periapical radiographs of mandibular second premolar and first molar of individuals of either sex aged 20–70 years residing in Chhattisgarh were taken by paralleling angle technique for the study. The RVG images of selected teeth were analyzed and height of the crown, i.e., coronal height and the height of the coronal pulp cavity, i.e., coronal pulp cavity height of each tooth were measured in millimeters using KODAK software to calculate TCI. The real age of a subject was compared with TCI of tooth and the acquired data was subjected to Pearson's correlation test. Bland and Altman regression analysis was carried out to estimate limit of agreement between the two measurements (real and calculated age). Results: Negative correlation was observed between the real age and TCI of mandibular first molar (r = −0.149, P = 0.166) and second premolar (r = −0.20, P = 0.061). The difference between real age and calculated age for premolar ranged from − 38.11 to 23.51 years (mean difference 7.30) and for first molar it was from − 34.82 to 25.22 years (mean difference 4.799), which suggested acceptable agreement. Conclusion: TCI method provides accurate estimation of age from RVG images of teeth. RVG is convenient to use, has low radiation dose, and produces sharper images than other imaging methods

Dietary Agents and Phytochemicals in the Prevention and Treatment of Experimental Ulcerative Colitis

Inflammatory bowel diseases (IBDs), consisting mainly of ulcerative colitis (UC) and Crohn's disease (CD), are important immune-mediated diseases of the gastrointestinal tract. The etiology of the disease includes environmental and genetic factors. Its management presents a constant challenge for gastroenterologists and conventional surgeon. 5-Amninosalicylates, antibiotics, steroids, and immune modulators have been used to reduce the symptoms and for maintenance of remission. Unfortunately, long-term usage of these agents has been found to lead to severe toxicities, which are deterrent to the users. Pre-clinical studies carried out in the recent past have shown that certain dietary agents, spices, oils, and dietary phytochemicals that are consumed regularly possess beneficial effects in preventing/ameliorating UC. For the first time, this review addresses the use of these dietary agents and spices in the treatment and prevention of IBD and also emphasizes on the mechanisms responsible for their effects