27 research outputs found
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Electric power system concepts for integration of advanced sensor and pulsed loads in the DDG-51 class ships
Advanced weapons and sensors increase demand on the electric power systems of Navy surface combatants, driving the need for fully Integrated Power Systems (IPS) such as those found in the DDG-1000 Zumwalt class of ships. The goal of this paper is to introduce novel power system configurations that could potentially be integrated into future flights of the DDG-51 class to support expanded electric power system capability at reasonable cost. Two concepts are presented: the first addresses the need for additional power for advanced sensor systems and the second addresses the need for a more significant increase in capacity to support higher power electric loads.Center for Electromechanic
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MVDC and HFAC Electric Power System Architectures for the Transformable Sea Base Connector (T-Craft)
The paper presents high frequency ac (HFAC) and medium voltage dc (MVDC) power system architectures for a notional T-Craft concept design and provides a qualitative comparison of relevant performance parameters. In particular the following items are discussed as worthy of attention in view of the large potential benefits they could produce: Risk mitigation in operating multiple series and parallel connected power conversion modules for both rectification and inversion at multi-megawatt power levels and high peak operating frequency. Synchronous drive topology offering the potential benefit of eliminating the need for multi-megawatt power conversion without compromising capabilities or performance: this would significantly reduce risk by eliminating much of the power electronics and the attendant size, weight and cost. Circuit protection strategies and components, for either HFAC or MVDC, for a flexible architecture suitable for fault management and reconfiguration. Integration of compact, lightweight gearboxes, either conventional planetary or advanced magnetic gear type, with existing designs for high-speed motors at the power level required by T-Craft. Critical technical issues for each power system architecture are identified and proposed simulation and technology development activities are described.Center for Electromechanic
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Inconsistencies in Electric Motor Certification Requirements
The Final Rule on certification requirements for induction motors issued by the Department of Energy contains different assumptions for the compliance and the enforcement procedures. These differences may yield unexpected results under certain conditions. For example, at times, the enforcement procedure can support a higher nameplate rating for a motor lot than would be possible by an appropriate application of the compliance procedure and vice versa. This paper examines, in detail, the nature of the problem and gives several examples where the enforcement plan fails to achieve its intended purpose.Center for Electromechanic
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High speed induction motor and inverter drive for flywheel energy storage
The use of flywheels to store energy is a technology which is centuries old. The confluence of several modern technologies has resulted in flywheels becoming a viable solution for the needs of the transportation, electric utility, and aerospace industries. This paper discusses a high-speed induction motor and its associated inverter drive which were developed for the Federal Railroad Administration’s “Advanced Locomotive Propulsion System.” The design of the induction motor provided several significant challenges. A megawatt rated, 12,000 rpm motor operating at a rotor surface velocity speed of 230 m/s required a unique mechanical configuration to withstand the centrifugal forces as well as an electromagnetic design, which produced a high efficiency at 200 Hz. Extending the design practices used in smaller motors would not achieve the goals required for a megawatt size machine. Similarly, the inverter was developed using a soft switching technique in order to meet the demands of high power output in a compact package. Application requirements, electrical and mechanical features of the motor, design strategy for the inverter, and test results are all presented in this paper.Center for Electromechanic
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Circuits for Protecting and Triggering SCRs in High-Power Converters
The performance of high-power converters employing silicon controlled rectifiers (SCRs) operating at several kilovolts and switching several thousands of amperes is strongly dependent on the triggering circuit and the protecting circuit (snubber) used. In this paper two standalone trigger circuit topologies are discussed and test results are given for one of them in particular, built with off-the-shelf components. A standard snubber circuit configuration was used and its ability to protect the SCR was examined by classical analytical methods and by computer simulation. Results of these calculations are reported as well as predictions about the fault tolerance afforded by the snubber design to a high power converter using SCRs. Since the components of the SCR protective circuits strongly affect the overall package size of the converter and tend to determine the minimum size and weight achievable, a conceptual design is also presented for a combined snubber-trigger circuit with the potential for reduced size and weight for the whole assembly.Center for Electromechanic
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Effect of Converter Packaging Techniques on Device Electrical Conduction
High power converters handling several thousands of amperes and employing solid state switches (silicon controlled rectifiers, or SCRs, for example), often have to use multiple devices in parallel. Additionally, if the converter operates across a high voltage bus, it may also require a series/parallel combination of SCRs. It is clear, therefore, that multiple conducting paths are created in any one leg of the converter. Because of mechanical requirements and practical considerations regarding the mounting of the SCRs and the routing of power to them, differential reactances are generated among the different paths, leading unavoidably to unequal current sharing among the various SCRs. This serious consequence may limit the effective current that can be switched or force the use of larger devices, if this is possible. It is very important, therefore, to be able to estimate the actual current distribution among the various power switches for a given realization of the converter. This paper discusses the problem as it was experienced in the actual implementation of a three-phase SCR bridge converter. The system geometry is described and the results of the electromagnetic finite-element analysis of one leg of the converter are given, highlighting the expected current distribution unbalance.Center for Electromechanic
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Intelligent Microgrid Demonstrator
The Center for Electromechanics at the University of Texas at Austin has a microgrid demonstrator capable of operating at power levels up to 2 MW. The microgrid is designed to interface with the commercial power system and other distributed sources of electric power, both ac and dc. It incorporates local prime movers that drive generators, both conventional 60 Hz and high frequency ac (800 Hz), as well as energy storage units. The microgrid is designed as a flexible system, easily expandable in power and re-definable in terms of voltage levels and system configuration. Several grid architectures have been studied and simulated, including a variety of pulsed and intermittent duty loads, as they can be found on US Navy ships. One problem under investigation is that of dc bus stability under the influence of constant power loads: these loads are known to induce instability at kW power levels but experimental data is very limited at MW power levels which are more representative of the situation on a ship. This paper describes the microgrid architecture, simulation results and data collected to date, as well as plans to demonstrate critical issues like stability, reconfigurability, fault management, integration of renewables, and model validation.Center for Electromechanic
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Modeling and Simulation Roadmap to Enhance Electrical Energy security of U.S. Naval Bases
The enhancement of the electrical energy security of Navy bases within the continental U.S. has been studied using an approach based on modeling and simulation, with the intent to achieve real time control and energy management. The commercially available software packages are reviewed and the most suitable ones are indicated. A notional base was developed and used for this study. Its format is general enough to be able to be used as a template for each specific Navy installation. Several preliminary simulations using commercial software have been performed on the power system of this notional base addressing a variety of operating scenarios including islanded mode and the impact of wind and solar power sources. Results of steady state and transient operation are also reviewed. The results of these simulations indicate that existing software packages available today, with proper adaptations, can provide a well validated and consistent process for evaluating power system architectures and technologies and, therefore, can become a valuable tool for the implementation of the described plan for Navy bases. The study concludes giving the details of the roadmap to move forward in the process of energy security enhancement of U.S. Navy bases through modeling and simulation.Center for Electromechanic
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Analytical Description of a Series Fault on a DC Bus
The solution of the equations of a dc circuit containing an arc is given and compared with experimental data. The arc is modeled according to its classical equivalent circuit and the adequacy of this model is discussed. The analytical solution for the circuit with an opening gap is given for the case of a constant gap and the results are extended to the cases of a gap opening with uniform velocity and a gap opening with constant acceleration, under the assumption of a quasi-static approximation for which the limits of applicability are estimated. Voltage and current evolutions in time are derived, including an estimate of the arc duration and quenching time. The results are compared to experimental data. Also provided is a generalized view of the transient behavior of an arc in a circuit that extends the description commonly used, in terms of only a voltage-current relationship, by also including inductive effects.Center for Electromechanic
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Challenges in the Design of a 100 kW Induction Motor for a PHEV Application
This paper summarizes some design challenges encountered in the development of a high speed induction motor/generator for a plug-in hybrid electric vehicle (PHEV). The traction system motor/generator was developed for integration into a high performance full-sized passenger car being developed by a major automotive manufacturer. The paper summarizes the traction motor performance requirements and presents the electromagnetic, mechanical and thermal design issues of the high speed 100 kW peak power induction machine.Center for Electromechanic