-This paper presents advancements in induction motor endring design to overcome mechanical limitations and extend the operating speed range and joint reliability of induction machines.A novel end ring design met the challenging mechanical requirements of this high speed, high temperature, power dense application, without compromising electrical performance. Analysis is presented of the advanced endring design features including a non uniform cross section, hoop stress relief cuts, and an integrated joint boss, which reduced critical stress concentrations, allowing operation under a broad speed and temperature design range. A generalized treatment of this design approach is presented comparing the concept results to conventional design techniques. Additionally, a low temperature joining process of the bar/end ring connection is discussed that provides the required joint strength without compromising the mechanical strength of the age hardened parent metals. A description of a prototype 2 MW, 15,000 rpm flywheel motor generator embodying this technology is presented.

Abstract-The University of Texas at Austin Center for Electromechanics (UT-CEM) is currently developing anAdvanced Locomotive Propulsion System (ALPS) as part of the Next Generation High-Speed Rail program sponsored by the Federal Railroad Administration (FRA). The ALPS consists of a gas turbine and synchronous alternator, combined with an induction motor coupled flywheel energy storage system (FESS). The prime power and FESS are coupled through a DC power link, as is the conventional AC traction drive system. The energy system includes auxiliary support systems to provide thermal management, bearing systems, controls, and power conversions. The energy exchange capacity of the flywheel is 360 MJ (100 kWhr). This paper presents the requirements, considerations, and design of the integrated turbine and flywheel power system. Significant development efforts have gone into the high-speed synchronous alternator, the flywheel power converter, the highspeed induction machine for the flywheel, the flywheel itself and its magnetic bearings. The fabrication status of these components and testing progress is also reported.

The University of Texas at Austin Center for Electromechanics (UT-CEM) is currently engaged in the development of an Advanced Locomotive Propulsion System (ALPS) for high speed passenger rail locomotives. The project is sponsored by the Federal Railroad Administration as part of the Next Generation High Speed Rail program. The goal of the ALPS project is to demonstrate the feasibility of an advanced locomotive propulsion system with the following features: • Operation up to 150 mph on existing infrastructure; • Acceleration comparable to electric locomotives; • Elimination of $3–5M per mile electrification costs; • Fuel efficient operation with low noise and exhaust emissions. The propulsion system consists of two major elements: a gas turbine prime mover driving a high speed generator and an energy storage flywheel with its associated motor/generator and power conversion equipment. The 2.5 MW high speed generator is a three phase, eight pole synchronous machine designed to directly couple to a 15,000 rpm gas turbine. Power from the turbine/alternator system feeds the locomotive dc bus through a conventional full bridge rectifier. The energy storage flywheel features a graphite/epoxy composite rotor operating on active magnetic bearings and is designed to store 480 MJ at 15,000 rpm. An induction motor/generator and variable frequency motor drive provide the link to the dc bus and are used to control power flow into and out of the flywheel. In addition to design and fabrication of the propulsion system components, the project is also developing a distributed control system with power management algorithms to optimize the hybrid propulsion system. Fabrication of the major components of the propulsion system is nearing completion and some preliminary testing of the flywheel and high speed generator has been completed. After completion of the laboratory testing, the propulsion system will be integrated onto a locomotive platform for rolling demonstrations at the Transportation Technology Center test track in Pueblo, Colorado. The paper presents an overview of the propulsion system operation and control strategies, gives detailed descriptions of the major components, and presents component test results.

Recent technological advancements in variable frequency drives have extended the capabilities of induction motors to servo control applications.The performance characteristics of these motors, however, are inherently fixed by critical design parameters, most notably rotor resistance. The ability to actively adapt the torque-speed characteristics of induction machines to match load requirements would significantly enhance their servo control capabilities. This paper describes the development and experimental demonstration of a solid-state switching network that actively modifies the performance characteristics of a wound-rotor induction motor, enabling real-time impedance matching with its mechanical load. This switching network manipulates the rotor currents of the motor to modify the torque and efficiency characteristics as a function of rotor speed. Perturbation and simulation studies establish the active range of induction motor torque that rotor resistance can control. Analytical control strategies are developed that enable the motor to operate at peak torque at all speeds. For implementation, a switched ballast network is inserted into the rotor circuitry of a wound-rotor induction motor.The modified motor is tested and the experimental results confirm the viability of this approach.

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