Page 365 - Power Electronics Handbook

Chapter 14
Power semiconductor circuit applications

14.1 Introduction

The preceding chapters have already described a variety of applications for
power semiconductors, such as static switching, a.c. line control,
phase-controlled rectification and inversion, frequency changers like
inverters and cycloconverters, and d.c. to d.c. converters or choppers.
When describing these applications the main consideration was for
analysing the systems from a circuit design point of view. In the present
chapter applications will be considered from another aspect, that of usage,
although the circuits within each of these groups will already have been
described in an earlier chapter. For example, inverters and choppers are
used within power supplies, phase-control rectification and inversion in
d.c. motor control, and so on.
Although there are a large number of different applications for power
semiconductors only a few of these are described here, and they are
grouped into four sub-sections: power supplies; electrical machine control;
heating; and electrochemical.

14.2 Power supplies

A power supply, or a power source, is anything which is capable of
providing energy. With this loose definition almost everything is a power
supply, although what is usually referred to by this term is equipment used
to provide stabilised and closely regulated d.c. voltage and current output
from an ax. mains input, or from a d.c. source such as a battery. There are
many ways in which this can be achieved, a few of these being shown in
Figure 14.1. Many of the functions shown are commercially available in the
form of integrated circuits, often the logic control circuitry and the power
switches being incorporated into the same die to form a smart power device
(Alegro, 1995; Bush, 1995; Dallimore and Carter, 1995). In these power
supplies, however, it is important to isolate the output from the input, and this
is usually done by a transformer.
Figure 14.l(a) shows a power supply arrangement in which voltage
regulation is applied to the a.c. input. This regulation technique can use
any of the methods described for a.c. line control in Chapter 8, although

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