Michelle Bash

Modeling of Salient-Pole Wound-Rotor Synchronous Machines for Population-Based Design

In recent years, population-based methods (evolutionary algorithms, particle swarm methods, etc.) have emerged as an effective tool for component and system design. Although relatively straightforward to apply, to capitalize on their potential, one must be able to explore a large design space. Herein, a magnetic equivalent circuit model is described to enable large-design-space exploration of salient-pole wound-rotor synchronous machine drive systems. Specifically, the model has been derived to evaluate machines with an arbitrary number of poles, stator slots (integer slots/pole/phase), winding layout, magnetic material, and a wide range of stator and rotor geometries. In addition, the model and solution technique have been structured to minimize the computational effort. An important attribute of the model is that saturation is handled with relatively few iterations and without the need for a relaxation factor to obtain convergence.

A Medium Voltage DC Testbed for ship power system research

Medium voltage dc distribution systems are currently of interest for future naval warships. In order to provide hardware validation for research associated with the development of these systems, a low power Medium Voltage DC Testbed (MVDCT) is being constructed. This paper documents the system being constructed and provides some initial test results.

Incorporating Motion in Mesh-Based Magnetic Equivalent Circuits

Recent research has compared the numerical efficiency of magnetic equivalent circuit (MEC) models based upon Kirchhoffs voltage law (mesh equations) and Kirchhoffs current law (nodal equations). For stationary magnetic components, it was shown that mesh-based methods converge in significantly fewer iterations. Although the numerical advantages would seemingly apply to electric machines, two issues have limited the application of mesh-based MEC models to electric machines. With movement, the number of meshes (unlike the number of nodes) is position dependent. Additionally, the loss of an airgap element creates an infinite reluctance. In this paper, both issues are addressed. Specifically, it is first shown that a relatively straightforward algorithm can be used to dynamically update meshes with rotor position. In addition, it is shown that the mesh model remains stable for very large values of tube reluctance. Tube reluctance values that are large enough to cause numerical issues can be easily avoided by excluding a very narrow range of rotor positions. Based upon these results, a mesh-based MEC model of a wound-rotor synchronous machine is developed and is shown to provide a significant advantage over its nodal-based model equivalent.

Analysis and Validation of a Population-Based Design of a Wound-Rotor Synchronous Machine

In recent research, a new magnetic equivalent circuit model and solution technique were developed to enable rapid calculation of the performance of wound-rotor synchronous machines. Herein, the development of a population-based design tool that utilizes the MEC is first described. The design tool is then applied to perform multiobjective optimization of a 2-kW portable power generator. Validation has been achieved through construction of a machine that was selected from the Pareto-optimal front (POF) of mass versus loss. Comparisons are made between designed and measured torque (instantaneous and average), open-circuit voltage, efficiency, and q- and d-axis flux linkages. This comparison is done in light of observations that the anhysteretic BH curve for the steel material obtained prior to and subsequent to machine construction have significant differences. Despite the variance, the measured and expected performances match reasonably well. Finally, an analysis of the machines on the POF is used to shed light on several interesting trends in design variables.

A comparison of permanent magnet and wound rotor synchronous machines for portable power generation

Permanent magnet and wound rotor synchronous machines (PMSMs and WRSMs) are often used in diesel engine-based portable power generation systems. In these applications, there is a growing desire to improve machine efficiency in order to reduce fossil fuel requirements. In addition, there is a desire to reduce mass to improve mobility. To attempt to address these competing performance objectives, a system analyst is confronted with numerous choices, including machine type (PM or WR), converter architecture (active/passive), and control. Herein, to assist the analyst, design tools capable of performing automated multi-objective optimization of PMSMs and WRSMs connected to both active and passive rectifiers are described. The tools are then used to derive tradeoffs between mass and efficiency for a 3 kW application.

Incorporating Dynamics in a Mesh-Based Magnetic Equivalent Circuit Model of Synchronous Machines

A mesh-based magnetic equivalent circuit has been derived to model the dynamics of wound rotor synchronous machines (WRSMs). A particular focus has been placed on the derivation of flux tubes to model machines with an arbitrary number of damper bars placed at an arbitrary depth in the rotor pole tip. Faradays Law is applied to establish a state model in which winding and damper bar flux linkages are selected as state variables. The resulting coupled magnetic equivalent circuit/state model is solved to predict machine dynamics. An important attribute of the model is that saturation is represented without the need for a relaxation factor, which enables its use as a practical tool in machine design. Data obtained from hardware experiment and a finite-element model are used to validate the proposed methods.

A magnetic equivalent circuit for automated design of wound-rotor synchronous machines

In this research, a magnetic equivalent circuit (MEC) model for population-based design (PBD) of salient-pole wound-rotor synchronous machines (WRSMs) is derived. The model includes a unique approach to represent fringing flux to the rotor poles based upon observations of flux paths seen in finite element solutions. In addition, the airgap flux tubes are simplified by including rotor fringing as separate static flux tubes. Finally, the flux tubes representing the rotor pole tip are selected to more effectively capture localized saturation. To enable rapid evaluation of design candidates, a mesh-based solution is applied to solve the MEC. A mesh approach is selected since it has been shown to have superior convergence properties compared to nodal-based models. The MEC model has been shown to match well with finite element (FE) models and measurements.

Alternative excitation strategies for a wound rotor synchronous machine drive

Excitation strategies are explored as part of an overall design to minimize mass and maximize efficiency of a 2 kW portable power generator. The design includes 16 variables and is based upon a magnetic equivalent circuit model that includes core loss. Despite the influence of saturation and core loss, a relatively straightforward field-oriented type control is derived that is consistent with the goals of mass and loss reduction. Design and control are validated through hardware experiment.

Design of an air-core linear generator drive for energy harvest applications

Vibration-based energy harvest is of interest in numerous applications. In this research, a focus has been on the design of air-core permanent magnet based energy harvest systems. To facilitate design, a toolbox has been derived that enables one to rapidly evaluate the performance of alternative magnet geometries, coil structures, energy storage devices, and circuit topologies. As an example, the toolbox has been applied to optimize the design of a hand-powered flashlight. Through this example, it is shown that coil structure and magnet length have a significant effect on energy harvest performance.

Trends on the Pareto-optimal fronts of a portable generator drive system

In recent research, magnetic equivalent circuit (MEC)-based tools have been developed to enable multi-objective optimization of wound-rotor synchronous machines (WRSMs). The tools have been validated through comparison with finite element based models and hardware experiment. Herein, a focus is placed on the analysis of the machines on the Pareto-optimal fronts (POF) of a 2 kW WRSM drive system. Various POFs have been created under alternative design constraints. The analysis is used to shed light on several interesting trends in design variables including pole count, d-axis stator current, turns, and airgap.