A high power wide bandwidth switch mode amplifier

This thesis describes the development of a 45kVA, 20kHz bandwidth switching amplifier. The amplifier is a subsection of a controlled source audiomagnetelluric (AMT) system primarily aimed at exploration of mineral deposits and geophysical deposits associated with oil and gas fields. However this amplifier has applications in many other areas.

A number of design innovations contributing to the body of knowledge in power electronics were implemented in the course of the development of the AMT amplifier. In particular, a new bridge inverter topology has been developed which supports five level pulsewidth modulation with only four switches. In the past eight switches have been required to achieve the same result. The five level modulation has allowed extension of the bandwidth and improvement in the output quality of the amplifier without increase in the switch frequency.

The new bridge topology consists of four buck converter sub units coupled by transformers. The buck converters supply a maximum current of l00A from a 560V nominal bus and switch at 50kHz. Each buck converter employs an Insulated Gate Bipolar Transistor and high speed power diodes together with a regenerative snubbing and clamp system to achieve this high power frequency product. New techniques have been developed to accurately predict diode reverse recovery performance during of the buck converter design process.

The new converter topology requires a specialised control system. The design of this control system, as well as important design rules developed during the project,

are presented.

Computer simulation studies have been extensively used in the design of both the buck converters and the control system. This design approach has resulted in a significant reduction in time consuming prototype modifications.