Rajeev Kumar Singh

Comparative performance evaluation of various fringe thinning algorithms in photomechanics

In recent years several algorithms have been reported for automating fringe data collection in photomechanics using the technique of digital image processing (DIP). Recent advances in phase shifting interferometry have offered some hope for full automation of static problems. However, for real-time dynamic studies conventional recording of fringes is a must. Fringe thinning is a very crucial step in extracting data for further processing. The various DIP algorithms for fringe thinning are surveyed and an attempt is made to explain better the mechanism of fringe skeleton extraction by various algorithms. The algorithm of Ramesh and Pramod is improved to extract fringe skeletons from saddle points in the fringe field. A cornparative performance evaluation of these algorithms is discussed with respect to the quality and accuracy of fringe skeleton extracted and the processing time. Performance evaluation is done on a few computer-generated. test images and also on images recorded by the technique of photoelasticity. The improved version of the algorithm of Ramesh and Pramod is found to give better fringe skeletons; it is also the fastest and the processing time is an order of magnitude less than the other algorithms. It is proposed that these computergenerated test images could be used as standard test images for checking the performance of any new fringe thinning algorithm.

Design and analysis of a modular magnetically coupled quadratic boost topology with a damping network for DC microgrid

High voltage conversion ratio converter is required in broad range of applications such as microgrid, hybrid electrical vehicles, telecommunication and medical equipments. The control-to-output transfer function of a conventional quadratic boost converter reveals that right half plane (RHP) zero exist, which makes the controller design difficult. The device has to operate on extremely high duty cycle (to get high voltage conversion) and this leads to severe reverse recovery problem and increases EMI. In this paper, a modular magnetically coupled quadratic boost (MMCQB) topology with damping network for DC microgrid is proposed. The proposed topology consists of a magnetically coupled quadratic boost converter with damping network and a modular controller. In the proposed MMCQB converter the inductors of a quadratic boost converter are magnetically coupled and damping network is introduced. This arrangement facilitates complete elimination of RHP zero and thereby making it a minimum phase system unlike the conventional quadratic boost converter. This also facilitates simple controller design and better dynamic performance. The proposed MMCQB converter provides high step-up gain of 17-18 times. The proposed MMCQB topology is capable of accepting both DC and AC microsources. Detailed design and analysis of the MMCQB topology are carried out. Steady state and dynamic modeling are carried out to exhibit the advantages of the MMCQB topology. Finally, a prototype circuit is implemented to verify the performance of the proposed concept.

Passive Vibration Damping Using Polymer Pads With Microchannel Arrays

Passive vibration control using blocks of viscoelastic materials with macro- and microscopic inclusions has been widely investigated. Significant changes in the vibration response have been observed with such inclusions. We have found that their response changes much more significantly if thin microstructures and channels are carved within these materials and are filled with a high-viscosity fluid. In this paper, we report the passive response of a replicated array of oil-filled microchannels, structured within a block made up of polydimethylsiloxane. Constrained and unconstrained vibration-damping experiments are performed on this block, wherein its vibration suppression ability is detected by applying an excitation signal transversely at the geometric center of the lower face of the block. We observe an increase in the fundamental frequency due to change in stiffness of the block and an increase in damping ratio and loss factor owing to the development of a slip boundary condition between the oil and the microchannel walls causing frictional dissipation of the coupled energy. All vibration experiments have been performed using a single-point laser to ascertain the experimental behavior of the system. We have also modeled the vibration suppression characteristics of such systems both analytically and by using simulation tools.

Minimum phase hybrid coupled inductor quadratic boost inverter

In this paper, a minimum phase hybrid coupled inductor quadratic boost inverter (QBI) is proposed for DC microgrid applications. Microsources such as solar photovoltaic (PV), fuel cell, wind power, etc. are low voltage generation sources and to meet out the grid requirement a high voltage gain converter is required. Most of the hybrid boost and buck-boost drive inverters found in literature have a right half plane (RHP) zero problems (i.e. non-minimum phase system) and operating range limited to 0.5 duty cycle. With a non-minimum phase control-to-output transfer function, it is hard to obtain adequate phase margin and has bandwidth problems. In the proposed minimum phase hybrid coupled inductor QBI, filter inductors are magnetically coupled and a series damping network is inserted. With this arrangement right half plane (RHP) zero is eliminated for DC boost operation, and thus, the system becomes a minimum phase that provides better dynamic performance. The QBI is capable of giving high step-up voltage gain up to 16-17 times. The proposed minimum phase hybrid coupled inductor QBI provides simultaneous AC and DC outputs with inherent shoot through protection in the inverter stage unlike the conventional voltage source inverter (VSI). A modified pulse width modulation (PWM) technique is also presented for the proposed minimum phase hybrid coupled inductor QBI. The proposed PWM method reduces the stress on the switches and the switching losses of the inverter. Steady state and small signal dynamic modeling are carried out to exhibit the advantages of the proposed hybrid QBI. The concept is validated through simulation and experimental verifications.

Unusual negative magnetoresistance in Bi2Se3–ySy topological insulator under perpendicular magnetic field

The magneto-transport properties of Bi2Se3–ySy were investigated. Magnetoresistance (MR) decreases with an increase in the S content, and finally, for 7% (i.e., y = 0.21) S doping, the magnetoresistance becomes negative. This negative MR is unusual as it is observed when a magnetic field is applied in the perpendicular direction to the plane of the sample. The magneto-transport behavior shows the Shubnikov–de Haas (SdH) oscillation, indicating the coexistence of surface and bulk states. The negative MR has been attributed to the non-trivial bulk conduction.

A novel GA optimized SHE PWM hybrid cascaded H-bridge multilevel inverter with Capacitor Voltage Averaging for motor drive applications

This paper proposes a new hybrid cascaded multilevel inverter (HCMLI) using selective harmonic elimination pulse width modulation (SHE-PWM) that synthesizes an eleven level output voltage with two dc sources and a pre-charged capacitor using twelve switches, in contrast to conventional twenty switches and five dc sources. Genetic algorithm (GA) has been used to compute switching angles of the HCMLI in this work. The proposed optimized HCMLI using SHE-PWM enables capacitor charge balance through an averaging scheme to reduce the steady state voltage error of the capacitor. The optimal structure for the proposed topology has been investigated for objectives such as minimum number of switches and lesser number of dc voltage sources for producing maximum output voltage steps.

A novel non-isolated magnetically coupled based bidirectional quadratic converter

This paper introduces a new magnetically coupled four-switches non-isolated bidirectional quadratic converter with a damping network for wide voltage conversion ratio. Due to its broad voltage conversion range in both ways, it can be easily suitable for the applications like hybrid electric vehicles (HEV), battery charging, uninterruptible power supplies (UPS), etc. Conventional bidirectional converter when operated in boost mode of operation suffers from right half plane (RHP) zero problems. Also, conventional bidirectional converter cannot operate to extremely high duty cycle or petite duty cycle. In this paper, two conventional boost converters are cascaded and diodes are replaced by bidirectional switches. The topology utilizes magnetic coupling of two inductors and a damping network. With this arrangement, RHP zero for the quadratic boost mode of operation will be completely eliminated and capable of handling large ripple currents in quadratic buck mode of operations. This enables simple and linear control of proposed bidirectional quadratic converter. The steady state analysis and small signal modeling are carried out. Finally, a prototype circuit is implemented to verify the performance of the proposed bidirectional quadratic converter.

Bidirectional quadratic converter for wide voltage conversion ratio

In this paper, a non-isolated bidirectional quadratic converter is proposed for wide conversion ratio. This proposed converter work as a quadratic boost converter as well as a quadratic buck converter in the same single converter. Due to its broad conversion range in both ways, it can be easily suitable for the applications like UPS, HEV, battery charging, etc. For high conversion ratio, converter needs to operate at an extreme duty cycle to achieve the highest possible gain. This activity leads to severe reverse recovery of the diodes, increases EMI, increase losses and decrease efficiency. For low conversion ratio, converter needs to operate at a low duty cycle to achieve the lowest possible gain but minimum turn on time is limited. The proposed bidirectional quadratic converter capable of providing wide voltage conversions ratio without operating extreme high or extreme low duty cycle. The steady state analysis and small signal modeling are carried out. Finally, a prototype circuit is implemented to verify the performance of the proposed bidirectional quadratic converter.

A modular high step up quadratic boost topology with minimum phase behaviour for microsource applications

A modular high step up quadratic boost topology with minimum phase behavior for microsource applications is proposed in this paper. The proposed topology is modular as it is capable of accepting both DC as well as high frequency AC supply generated by microsurces such as solar cell modules and wind turbines etc. In the proposed topology the right half plane (RHP) zero gets completely eliminated for the boost operation thereby making it a minimum phase system. This also facilitates simple controller design. The proposed topology gives very high step up gain (about 17-18 times) to increase the output voltage of the microsources up to 421 V from the input voltage of 24 V. Steady state and dynamic modeling is carried out for the proposed topology. Verification is done on a 400 W prototype by giving 90 V (peak-to-peak) AC supply and 24 V DC supply.