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5

Power semiconductor

devices and converter

hardware issues

5.1 Introduction

The advances of high voltage/current semiconductor technology directly affect the
power electronics converter technology and its progress. The `perfect' high-power
semiconductor is yet to be fully developed and become commercially available.
However, new semiconductors have changed the way that power switches are pro-
tected, controlled and used and an understanding of the device characteristics is
needed before a system is developed successfully.
Technological progress in the power electronics area over the last twenty years or
so has been achieved due to the advances in power semiconductor devices. In this
chapter, these devices are presented and current developments are discussed.

5.2 Power semiconductor devices

The various semiconductor devices can be classified into three categories with respect
to the way they can be controlled:
1. Uncontrolled. The diode belongs to this category. Its on or off state is controlled
by the power circuit.
2. Semi-controlled. The thyristor or silicon controlled rectifier (SCR) is controlled by
a gate signal to turn-on. However, once it is on, the controllability of the device is
lost and the power circuit controls when the device will turn-off.
3. Fully-controlled. Over the last twenty years a number of fully controlled power
semiconductors have been developed. This category includes the main kind of