26 research outputs found
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Modeling and Evaluation of a Plug In Hybrid Fuel Cell Shuttle Bus
The Center for Electromechanics at The University of Texas at Austin acquired a plug-in hybrid fuel cell bus for demonstration and model development under a program funded through the USDOT-FTA. The purpose of this program was to evaluate the performance and use of the bus while developing a model that could predict overall performance and energy consumption on daily driving routes. A model of the fuel cell bus was developed using PSAT (Powertrain Analysis Toolkit). The model development involved verifying component characteristics and a parametric study of drivetrain efficiencies to relate predicted to measured vehicle energy consumption data from on-road testing. The PSAT model was able to predict net energy consumption to within 5% over varying route profiles and vehicle conditions. Further investigations with advanced energy storage were performed to evaluate the benefits of ultracapacitor assisted batteries by using the correlated PSAT model. Ultracapacitors act as an additional load leveling device in the hybrid vehicle for peak propulsion and braking vehicle loads, thereby reducing stress on the batteries. The model simulation results show that ultracapacitors can increase overall vehicle economy by 2 to 4% and deliver a net increase in battery efficiency of 3 to 4%.Center for Electromechanic
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Thermoplastic applications for pulse power alternators
The field coil is the primary component of the rotor assembly that provides the rotating magnetic field for the pulse power alternator. The design of the field coil is optimized so that it will produce the required magnetic field with minimum transient losses. The high currents required to produce the correct amp-turns, along with the mechanical loads due to high rotational speeds, present further design requirements for selection of field coil material, insulation, and surrounding material that completes the matrix of the field coil sub-assembly. With the addition of active cooling requirements in the field coil design, surrounding materials must be selected that retain electrically insulative properties and are thermally conductive to allow sufficient heat removal from the field coil. Thermoplastics are now being reviewed to replace traditional glass-epoxy potting compounds (thermosets) that have been used extensively in pulsed alternator designs. Fillers can be added to tailor properties of the thermoplastic, such as ceramics to increase thermal conductivity at the cost of an increase in density. Thermal analyses have been performed that show the benefits of using thermally conductive potting compounds. In addition, subscale field coil mockups (motorettes) have been encapsulated and tested to demonstrate encapsulation of current field coil geometriesCenter for Electromechanic
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Transient 3-D thermal analysis for an air-cooled induction motor
For an induction motor that is cooled by an airflow ventilated across the air gap between the rotor and stator, the rotor end-ring and stator end-turn cooling might influence the motor temperatures in the core sections appreciably. Detailed motor thermal modeling is typically required to provide transient rotor temperature distributions for rotor structural analysis and to predict stator temperature distributions to assure the maximum stator temperature is below the stator insulation temperature limit. For an air-cooled induction motor, transient 3-D finite element thermal analyses for both rotor and stator have been performed in this paper. In the stator thermal model, the slot conductors and various insulations were smeared and equivalent thermal properties were used to reduce modeling and computational effort. Position-dependent and time-dependent air cooling boundary conditions, which include air temperatures and forced convection heat-transfer coefficients, were applied to the 3-D thermal modelsCenter for Electromechanic
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Electric Vehicle Modeling Utilizing DC Motor Equations
This paper discusses modeling an electric utility vehicle powered by a separately wound DC motor. Many modeling techniques use steady state efficiency maps and torque-speed curves to describe the performance of electric motors, which can overlook transient response dynamics, current limits, and thermal limits that may affect the end vehicle performance. This paper discusses using bond-graph techniques to develop a causal model of an electric vehicle powered by a separately wound DC motor and development of the appropriate feedforward and feed-back controllers required for route following. The causal model performance is compared to a PSAT model of the same electric vehicle, which uses motor torque-speed curve and efficiency map.Center for Electromechanic
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Field coil insulation testing for pulsed power alternators
Current pulse power alternator designs operate at high speeds and high current densities. The field coil insulation systems for pulse power alternators must provide sufficient stand-off voltage while limiting the amount of thermal resistance for actively cooled designs, and also withstand the strain excursions experienced at full operating speed. Repetitive cycling of the strain excursion overtime may induce cracks in the surrounding field coil matrix. The primary insulation surrounding the field coil conductors must be able to stop crack propagation that may develop in the surrounding matrix material and provide voltage hold-off. Thermally conductive thermoplastics are currently being investigated for the field coil matrix materials where decreased thermal resistance is necessary for actively cooled field coil designs. In order to evaluate conductor insulation and thermoplastic matrix filler quickly, small coupon motorettes were developed per previous designs. The motorettes simulate the hoop strain the conductors would experience due to rotor growth at high rotational speeds. Once the motorettes had been mechanically loaded, the coupon was hi-potted to verify insulation integrity under strain. This paper will discuss the design and testing of these motorettes to evaluate thermally conductive thermoplastics as filler material for the field coil matrixCenter for Electromechanic
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Splits of Windage Losses in Integrated Transient Rotor and Stator Thermal Analysis of a High-Speed Alternator During Multiple Discharges
For a high-speed electrical alternator, the rotor outer banding and stator inner liner are typically made of high strength graphite epoxy composites due to their high strength and stiffness. Machine structural integrity at high rotating speeds degrades significantly as the composite resins lose their strength at high temperatures. The magnitude of the frictional windage losses generated in the air gaps and the splits of the windage losses between the rotor and stator become crucial to the machine design since these windage losses greatly influence the rotor outer and stator inner surface temperatures. Splits of windage losses generated by an enclosed high-speed composite rotor in low air pressure environments were investigated by The University of Texas at Austin Center for Electromechanics and described in a companion paper. The windage splits are dictated by the air temperature gradients at the rotor outer and stator inner surfaces. Unique heating, cooling, and component material properties of a typical high-speed alternator during repetitive-discharge events make its transient air-gap windage splits very much different from those of the test setup. This paper describes transient windage splits in integrated rotor and stator thermal analyses of a high-speed alternator designed for multiple discharges. The transient windage splits in the air-gap air flow were obtained through multiple iterations on windage losses, air-gap air temperatures, and rotor and stator surface temperatures.Center for Electromechanic
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Empirical Data on High Flow Velocity Coolants in Copper Tubing and the Effects on the Coolant’s Electrical Resistivity
The electrical power generation industry has developed a set of guidelines and operating parameters for coolant fluids exposed to high voltage. These guidelines are very system-specific and limited to the operating range of standard utility power generation industries. There is a growing interest today in high energy density pulsed-power generation as well as >power on demand> energy storage devices such as flywheel battery systems. The University of Texas at Austin Center for Electromechanics (UT-CEM) is a leader in the development and prototype testing of such energy storage devices. This paper describes a coolant flow test apparatus at UT-CEM that was used to obtain empirical data for coolant flow in copper tubing. Different test coolant fluids were run though a mock electrical coil with real time fluid parameters monitored and recorded for later analysis. This system recorded and stored fluid flow rate, fluid temperature, fluid pH level, fluid electrical conductivity, and several system pressures around the fluid circuit. This testing provides an expanded data base and additional guidelines for coolant system performance in high energy density power generators.Center for Electromechanic
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Electrically Dewatering Microalgae
Microalgae are being developed as a source of fuels and/or chemicals. A processing challenge is dewatering the algae. Electrical approaches to dewatering include exploiting electrophoresis or electroflocculation. The reported experiments show that electrophoresis does occur but is complicated by the effects of the fluid motion. It appears that the coupling of the algal cell and the fluid can be sufficiently strong such that fluid motion effects can influence or dominate behavior. Electroflocculation appears to be a robust process. It does, however, inherently leave electrically induced trace metal flocculants in the dewatered algae.Center for Electromechanic
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Design and Demonstration of an Extended Range Hydrogen Fuel Cell Utility Vehicle
This paper discusses the design, build, and demonstration of two hybrid electric fuel cell utility vehicles for a program sponsored by DLA (Defense Logistics Agency). The design emphasis for the utility vehicles was range extension over state of the art battery systems using a fuel cell power plant. The design work involved vehicle modeling in PSAT to evaluate different battery technologies and compare the effects of different hydrogen storage technologies on vehicle performance and overall range. The comparative analysis showed that 350 bar compressed hydrogen storage maximized vehicle range and produced a final vehicle design that demonstrated a 300+ mile range during commissioning trials.Center for Electromechanic