0195136047.pdf

750 BASIC CONTROL SYSTEMS

0

Maximum

continous

torque

Maximum

transient

torque

Maximum

continuous

power

Maximum

transient

power

III

Speed ωm

Maximum speed

−ωmb

ωmb

Torque T

IV

II I

Figure 16.1.3Continuous as well as transient torque and power limitations of a drive.

Power Semiconductor Devices

Since the advent of the first thyristor or silicon-controlled rectifier (SCR) in 1957, tremendous

advances have been made in power semiconductor devices during the past four decades. The

devices can be divided broadly into four types:

• Power diodes


• Thyristors


• Power bipolar junction transistors (BJTs)


• Power MOSFETs (metal-oxide semiconductor field-effect transistors).
  Thyristors can be subdivided into seven categories:


• Forced-commutated thyristor


• Line-commutated thyristor


• Gate turn-off thyristor (GTO)


• Reverse-conducting thyristor (RCT)


• Static-induction thyristor (SITH)


• Gate-assisted turn-off thyristor (GATT)


• Light-activated silicon-controlled rectifier (LASCR).
  Typical ratings of these devices are given in Table 16.1.2. Whereas this comprehensive table,
  as of 1983, is given here for illustration purposes only, several new developments have taken
  place since then: A single thyristor is currently available with the capability of blocking 6.5
  kV and controlling 1 kA. The 200-V Schottky barrier diodes are commercially available with
  ratings of several hundred amperes, up to 1 kA, and with blocking voltages as high as 1–5 kV.