David M. Beams

Failure mechanisms in MOSFET square-wave drivers for wireless power transfer applications

Reports from experimental laboratory work have described catastrophic failure of power MOSFETs used in square-wave voltage sources driving resonant four-coil wireless power-transfer (WPT) networks. Simulation with PSpice has duplicated the problem, identified its probable origins, and presents possible avenues for amelioration.

Calculation of mutual inductance from magnetic vector potential for wireless power transfer applications

Recent renewed interest in commercial development of wireless power transfer through magnetically-coupled resonant circuits has shown the need for a computational tool that can calculate the mutual inductance of coils of arbitrary geometry and spatial orientation. This task is often performed by finite-element analysis (FEA), but this requires both access to such software and a degree of expertise on the part of the designer. This paper introduces a simple-to-use Matlab-based computational tool for calculating mutual inductance for inductors in free space based upon magnetic vector potential.

Design and simulation of networks for midrange wireless power transfer

This paper presents the design and simulation of an efficient four-coil wireless power transfer (WPT) system using magnetically-coupled resonant circuits (MCRC). Simulations show that a system capable of transmitting power over a transmitter-to-receiver separation of 2m with efficiency exceeding 70% at a frequency of 100kHz.

Validation of a reflected-impedance design method for wireless power transfer applications

This paper proposes a simplified method for designing four-coil resonant wireless power transfer (WPT) networks by sequential application of impedance reflection through mutual inductances. Experimental validation is presented, and accuracy and limitations of the method are described. The method appears useful for first-pass (approximate) design, but accurate simulation requires consideration of mutual inductances of non-adjacent coils.

Modeling and simulation of off-line boost power factor correction (PFC) circuits

Electric power is delivered most efficiently from utilities to end users when the load draws current at unity power factor. Traditional ac-to-dc power supplies that use a rectifier/filter topology, however, draw currents that are highly non-sinusoidal and rich in harmonics and thus display a low power factor. An alternative approach, known as offline power factor correction, eliminates the filter capacitor and uses switchmode power converter techniques to achieve power factors close to unity. Commercially-available integrated circuits may be combined with external discrete components to make a complete offline power-factor correction circuit; however, the manufacturers data sheets frequently provide little theoretical basis for their application information. This paper deals with modeling and simulation work to derive the transfer functions of the voltage- and current-control loops, with a primary focus on the current-control loop. The transfer function of the current-control loop has been derived for specified operating conditions, and a Matlab script for plotting Bode plots of these transfer functions is developed.

State-variable analysis of wireless power transfer networks for linear and nonlinear loads

A state-equation approach to modeling wireless power transfer (WPT) networks is presented. The state-variable approach was investigated because it permits termination of the network in nonlinear loads, which is not possible with the usual analysis with the phasor transform. The modeling work presented here involves a three-coil WPT network terminated in a rectifier and filter; simulation has been carried out using constant-resistance and constant-power loads. The validity of the model was established by comparison with commercial circuit-analysis software.

Simulation of a switched series-resonant receiver for wireless power transfer applications

There has recently been considerable renewed interest in commercial development of wireless power transfer (WPT) through magnetically-coupled resonant circuits. One of the problems inherent in WPT is the large variation in power delivered to the load if the flux-coupling coefficient from primary to secondary resonators is allowed to vary. Power delivery may be regulated by either supply-side or load-side regulation, but load-side regulation is less complex as it does not require feedback from the load to the source. The paper analyzes through state equations a proposed method of load-side regulation and develops and validates a linearized model.

Beta Testing a Web-Based Writing Coach

“The Coach” is a web-based tool developed to guide students through the technical writing process. It provides instruction about form as well as critique of different aspects of the students’ writing. It goes beyond the Microsoft word spell check and grammar check. It gives feedback about writing complexity and appropriateness for different word choices in a technical document. It also gives background about the appropriate contents for technical writing in addition to example documents. The latter is extremely important for the novice writer who may not have much experience in working with technical reports.The initial document type in “The Coach” is a lab report. If the lab report can be developed into the web-based tool, other forms will be more easily implemented. In addition to developing the website, the development team is preparing a document and a video for a professor to use to instruct students on the use of “The Coach.”The instructional materials and “The Coach” were beta tested with a freshman engineering class. A baseline writing sample was collected before the introduction of “The Coach.” Students in some sections were instructed in use of “The Coach,” and other sections were controls. Additional beta testing is ongoing.© 2012 ASME

Small-signal modeling of boost power-factor correction controllers

Electric power is delivered most efficiently when the load draws current at unity power factor. Traditional rectifier/filter power supplies, however, draw currents that are highly non-sinusoidal and thus display a low power factor. An alternative approach, known as offline power factor correction (PFC), achieves near-unity power factor by eliminating the filter capacitor and using switchmode power converter techniques. Power-factor correction circuits are commercially available; however, manufacturers data sheets frequently provide little theoretical basis for their application. This paper deals with modeling and simulation work to derive the loop gain of a PFC with the goal of improving the tools available to design engineers. An expression has been derived for the loop gain of a PFC under specified operating conditions, and a Matlab script for plotting Bode plots of the loop gain is being developed.

Work in progress - developing student design consultants

Multidisciplinary capstone design experiences are generally favored by the professional engineering establishment. While logistically possible to arrange such an experience, particularly at smaller universities, maintaining a reasonable project scope and providing adequate depth of the experience for each discipline can be difficult. One approach involves using student consultants to provide support to multiple projects when there is insufficient content to provide a singular, substantive experience. This approach avoids oversubscribing faculty as de facto team members, while still providing a breadth based design experience for students. For example, electrical design projects at The University of Texas at Tyler frequently require development of a one-of-a-kind printed circuit board, but most electrical students are not familiar with CAD-based layout of artwork, design rules, and the processes used for board development. A process using an engraving laser has been developed for board production, but has required extensive involvement from mechanical engineering faculty. To prepare mechanical engineering students to provide future layout and fabrication assistance, motor drive circuits were developed and tested as part of a course in electro-mechanical systems design. While circuit schematics were provided, every student attempted the artwork and each team developed and tested a circuit board. This paper describes the results, and some lessons learned, from this initial attempt to develop student design consultant capability.