Heath F. Hofmann

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Conditions for observability of a linearized smoothairgap induction machine model are examined, and limitations of any speed-sensorless observer scheme based on such a model are discussed. An approach for speed-sensorless flux estimation based on singular perturbation theory is developed. This approach relies on the natural time-scale separation between the(More)
In many variable-torque applications of induction machines, it is desirable to operate the machine at high flux levels, thus allowing the machine to produce higher torques. This can lead to saturation of the main flux path, introducing crosscoupling effects which can severely disrupt the performance of controllers dependent on knowledge of the machine’s(More)
The recent development of electrostrictive polymers has generated new opportunities for high-strain actuators. At the current time, the investigation of using electrostrictive polymer for energy harvesting, or mechanical to electrical energy conversion, is beginning to show its potential for this application. In this paper we discuss the mechanical and(More)
In this paper, an active energy harvesting technique for a spring-mass-damper mechanical resonator with piezoelectric electromechanical coupling is investigated. This technique applies a square-wave voltage to the terminals of the device at the same frequency as the mechanical excitation. By controlling the magnitude and phase angle of this voltage, an(More)
This paper presents a position-sensorless vector torque controller designed to achieve maximum efficiency over a range of power and rotational speed for a synchronous reluctance machine. A model of the synchronous reluctance machine is presented which incorporates both winding and core losses. It is then shown that a stator-flux-oriented control scheme can(More)
A hybrid controller, consisting of a model-based feedforward controller and a proportional–integral feedback compensator, for a solid-rotor synchronous reluctance motor/generator in a high-speed flywheel-based uninterruptible power supply application is proposed in this paper. The feedforward controller takes most of the control output of the current(More)
One key parameter in using electroactive materials to harvest electric energy from mechanical sources is the energy conversion efficiency. Recently, it was shown that, in the relaxor ferroelectric PMN-PT single crystals, a very high longitudinal electromechanical coupling factor (>90%) can be obtained. This paper investigates energy harvesting using 1-3(More)
Shipboard electric propulsion systems experience large power and torque fluctuations on their drive shaft due to propeller rotational motions and waves. This paper explores new solutions to address the fluctuations by integrating a hybrid energy storage system (HESS) and exploring coordinated power management. A propeller and ship dynamic model, which(More)
An open-loop current regulator for a high-speed synchronous reluctance machine with a solid conducting rotor is presented. A rotor dynamic model is developed which is similar to an induction machine model yet includes a magnetic saliency of the rotor. The model is then used to calculate command voltages for a desired current in an open-loop current(More)