387,317 research outputs found
Flier for Girls Rock! DC concert at 9:30 Club, August 14, 2010
No full textFlier for Girls Rock! DC showcase at 9:30 Club on August 14, 2010. Flier features a drawing of a four-track recorder and headphones and the Girls Rock! DC logo
Girls Rock! DC 2010 official guide to rock
No full textBooklet containing a description of the Girls Rock! DC summer camp showcase mission and schedule for summer 2010, as well as tips and encouragement for beginning rock musicians
Cold cracking in DC-cast high strength aluminum alloy ingots: An intrinsic problem intensified by casting process parameters
No full textFor almost half a century the catastrophic failure of direct chill (DC) cast high strength aluminum alloys has been challenging the production of sound ingots. To overcome this problem, a criterion is required that can assist the researchers in predicting the critical conditions which facilitate the catastrophic failure of the ingots. This could be achieved at first glance by application of computer simulations to assess the level and distribution of residual thermal stresses. However, the simulation results are only able to show the critical locations and conditions where and when high stresses may appear in the ingots. The prediction of critical void/crack size requires simultaneous application of fracture mechanics. In this paper, we present the thermo-mechanical simulation results that indicate the critical crack size distribution in several DC-cast billets cast at various casting conditions. The simulation results were validated upon experimental DC-casting trials and revealed that the existence of voids/cracks with a considerable size is required for cold cracking to occur.Materials Science & EngineeringMechanical, Maritime and Materials Engineerin
A cryogenic dc-dc power converter for a 100kW synchronous HTS generator at liquid nitrogen temperatures
No full textA dc-dc converter has been developed for retrofitting inside the vacuum space of the HTS rotor of a synchronous generator. The heavy copper sections of the current leads used for energising the HTS field winding were replaced by cryogenic power electronics; consisting of the converter and a rotor control unit. The converter board was designed using an H-bridge configuration with two 5A rated wires connecting the cryogenic boards to the stator control board located on the outside of the generator and drawing power from a (5A, 50V) dc power source. The robustness of converter board was well demonstrated when it was powered up from a cold start at 82K. When charging the field winding with moderate currents (30A), the heat in-leak to the ‘cold’ rotor core was only 2W. It continued to function down to 74K, surviving several quenches. However, the quench protection function failed when injecting 75A into the field winding, resulting in the burn out of one of the DC-link capacitors. The magnitudes of the critical currents measured with the original current leads were compared to the quench currents, which was defined as the current which triggered quench protection protocol. The difference between the two currents was rather large, (~20A). However, additional measurements using a single HTS coil in liquid nitrogen found that this reduction should not be so dramatic and in the region of 4A. Our conclusions identified the converter’s switching voltage and its operating frequency as two parameters, which could have contributed to lowering the quench current. Magnetic fields and eddy currents are expected to be more prominent the field winding and its impact on the converter also need further investigation
Flier for a concert to benefit the DC Free Clinic featuring Fugazi, False Face Society, Crash Worship at St. Augustine's School, July 6
No full textFlier to benefit the DC Free Clinic featuring Fugazi, False Face Society, and Crash Worship at St; Augustine School on July 6. The flier features a quote on the footer stating, \you are not what you own....\ and in the background, Giorgio Beverly Hills perfume bottles
Behaviour of Modular Multilevel DC/DC ConverterWith DC Voltage Control Integrated in a Multi-terminal DC System Under Fault Conditions
No full textThe development of multi-terminal DC (MTDC) networks has various challenges as interconnecting grids of different voltages
and grounding schemes, DC grid protection and power flow. DC/DC converter has emerged as the solution for interconnecting
HVDC links with different specifications. In this paper, the Front-to-Front Modular Multilevel Converter (F2F-MMC) topology
is adopted for DC/DC converter, which can act as a firewall between the healthy and faulty grid during DC faults. Along with this,
DC/DC converters when operated in DC voltage control mode can provide supplementary functionalities such as participating in
DC grid voltage management and increasing the reliability of the system. In this study, the F2F-MMC converter is operated with
a virtual resistance DC voltage controller integrated into an MTDC system. A pole-to-pole DC fault is applied on the MTDC grid
and the influence of the virtual resistance controller associated with the DC/DC converter is studied for re-establishing the power
flow after DC faults
DC-DC converter current source fed naturally commutated brushless DC motor drive
No full textThe aim of this work is to reduce the cost and size of a brushless dc motor (BLDC) drive as well as increase the reliability and ruggedness of that drive. Traditional BLDC drives use Voltage Source Inverters (VSI) that utilize hard switching, thereby generating switching losses and entail the use of large heatsinks. VSI needs a huge dc link capacitor that is inherently unreliable and is one of the most expensive components of a drive. Hence, a Current Source Inverter (CSI) is used to replace the hard switchings by natural turn-off, thereby eliminating the heatsinks as well as the large dc link capacitor. A controlled rectifier together with a large inductor act as the current source. The only disadvantage is the large value of the dc link inductor and the huge number of turns needed to achieve these values of the inductances lead to huge resistive losses.
Therefore, it is shown that it is possible to replace the controlled rectifier and the large inductor with a suitable dc-dc converter based current source switching at high frequencies and a much smaller value of the dc link inductor. Switching at high frequencies makes it possible to reduce the value of the dc link inductor without increasing the current ripple. Hence, it is possible to have the advantages of using a CSI as well as reduce the value of the dc link inductor without a corresponding increase in the heat sink and snubber requirements
Flier for an AIDS benefit for the Carl Vogel Foundation and the ACT UP DC needle exchange program featuring Holy Rollers, Circus Lupus, Girls Against Boys and 3LG at Sanctuary Theater, December 18
No full textFlier for an AIDS benefit for the Carl Vogel Foundation and the ACT UP DC needle exchange program featuring Holy Rollers, Circus Lupus, Girls Against Boys and 3LG at Sanctuary Theater on Friday, December 18. All ages. Includes phone number for Positive Force DC for information. Features an illustration of a hand with snakes for fingers grasping the world and casting a shadow over a scared-looking man. Includes text \No-one is immune
Analysis of DC-Link capacitor losses in three-level neutral point clamped and cascaded H-Bridge voltage source inverters
No full textLoss estimation is a critical aspect of inverter design.The present work investigates the losses occurring in the
DC-link capacitors of the three-phase three-level neutral point
clamped and cascaded H-Bridge inverter topologies, by
performing a harmonic analysis of the capacitor currents.Results are verified by simulations. Their analysis reveals the
advantage of the NPC inverter
Common Mode Currents in DC Power Routers
No full textThe grid reinforcement and energy redirection needs have led to the emergence of Back-To-Back Voltage Source Converter (BTB-VSC) based dc power routers. This paper investigates the low frequency Common Mode Currents (CMCs) that arise in the system if the employed BTB-VSCs have an un-isolated ac path connected in parallel to their output ports. Simulation results are presented to show a sensitivity analysis of lower order harmonics in CMC with respect to the operating active and reactive power of the dc router, dc link voltage, link resistance, modulation method and pole capacitance. Experimental results are shared to show existance of lower order CMC in 3-wire ac link operating in parallel with the dc power router and these are mitigated using zero sequence controller
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