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MIT Electrical Engineering and Computer Science
EECS Announcement |
December 19, 2002
Mr. Williams received his B.S. in Electrical Engineering from Worcester Polytechnic Institute in 1984 and his M.E.in Electrical Engineering from Rensselaer Polytechnic Institute in 1987. He spent 7 years at MIT Lincoln Laboratory working with digital, analog, radio frequency, and microwave circuit designs for radar systems and high-reliability satellite communications systems. Prior to working at MIT Lincoln Laboratory, he worked at Harris RF Communications designing base stations for cellular telephone systems as well as at General Electrical Medical Systems working on magnetic resonant imaging systems. Before helping to start Heliotronics, he was a development engineer at Control Resources, Inc. designing fan speed controllers and alarms. In April 1998, Mr. Williams, together with Clayton Handleman, founded Heliotronics, Incorporated as an electrical engineering consulting and product development firm. Their mutual interest in renewable energy has led them to focus exclusively on product development for distributed generation with emphasis on grid-connected photovoltaics. Mr. Williams is presently leading the electrical development of Heliotronics' inverter. He is in charge of digital, analog, and power circuit design, PCB layout, manufacturing, testing, FCC compliance, and UL safety compliance. He has also enhanced, coded, and tested the firmware. In addition to the inverter, Mr. Williams is also the lead engineer for Heliotronics' SunLogger datalogger project. Besides product design, Mr. Williams is involved with national efforts to develop interconnection standards for distributed electrical generation such as PV systems. Abstract This talk presents the implementation of a waveshaping circuit for a utility-interactive DC-to-AC inverter for use with photovoltaic (PV) systems. Regulations in the USA and most other countries require that the output current waveform have low Total Harmonic Distortion (THD). Consequently a major task of the inverter is to provide a sinusoidal output in phase with the utility voltage. This talk will review both input and output requirements and present a method for providing a low output current THD using a buck converter as the waveshaping circuit. The talk will review basic methods of voltage- and current-mode PWM control as well as constant off-time current-mode control (COTCMC) that can be used with the buck converter. Finally simulated and measured results will be presented.