Power transistor switching amplifiers

Abstract

The comparative ease with which direct current machines can be controlled has led to their application in various fields and in order to achieve accurate and versatile control of the machine “Four quadrant” controllers have been developed over many years. Originally these controllers were of the “Ward Leonard” type, involving rotating machines. With the advent of mercury arc rectifiers static controllers were devised, and more recently the development of high power thyristors as the main power control element has enabled solid state four quadrant controllers to be reliable and cheap.

However, the introduction of a new series of high power transistors with improved ratings, static controllers using power transistors as the power control element are becoming more feasible. Several controllers have already appeared on the market but with limited capacity since transistor development still lags behind that of the thyristor. The transistor being a fully controllable element (requiring no “turn-off” mechanism) easily lends itself to switching amplifiers for motor control applications. These switching amplifiers are capable of producing a good frequency response at high overall efficiency.

It is the aim of this dissertation to investigate the possibilities of producing switching amplifiers for the control of alternating and direct current machines.