Page 174 - Electrical Equipment Handbook _ Troubleshooting and Maintenance

Source: ELECTRICAL EQUIPMENT HANDBOOK

CHAPTER 9
POWER ELECTRONICS,

RECTIFIERS, AND

PULSE-WIDTH

MODULATION INVERTERS

INTRODUCTION TO POWER ELECTRONICS

The development of solid-state motor drive packages over the last 30 years has revolu-
tionized the application of electric motors. Any power control problem can be solved using
them. The solid-state drives allowed dc motors to run from ac power supplies or ac motors
from dc power supplies. The frequency of ac power can be changed to any other frequency.
Furthermore, the reliability of solid-state drive systems has increased while their costs
have decreased. The versatility of these solid-state controls and drives has provided many
new applications for ac motors which were formerly covered by dc machines. The appli-
cation of solid-state drives has also provided flexibility for dc motors.
The development and improvement of high-power solid-state devices have caused this
major change.

POWER ELECTRONICS COMPONENTS

The most important types of semiconductor devices are
1. The diode
2. The two-wire thyristor (or PNPN diode)
3. The three-wire thyristor [or silicon controlled rectifier (SCR)]
4. The gate turnoff (GTO) thyristor
5. The DIAC
6. The TRIAC
7. The power transistor (PTR)
8. The insulated gate bipolar transistor (IGBT)

The Diode
A diode is a semiconductor device that conducts current in one direction only (Fig. 9.1). The
current is conducted from its anode to its cathode, but not in the opposite direction.

9.1
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