0195136047.pdf

754 BASIC CONTROL SYSTEMS

• Ac–ac converters (ac voltage controllers)


• Dc–dc converters (dc choppers)


• Dc–ac converters (inverters)


• Static switches (contactors), supplied by either ac or dc.
  Figure 16.1.5 shows a single-phase rectifier circuit converting ac voltage into a fixed dc
  voltage. It can be extended to three-phase supply. Figure 16.1.6 shows a single-phase ac–dc
  converter with two natural line-commutated thyristors. The average value of the output voltage
  is controlled by varying the conduction time of the thyristors. Three-phase input can also be
  converted.

+

Diode D 1

Diode D 2

Ac

supply

R

Vm

Vm

−Vm

π

π 2 π

2 π

vs

vs = Vm sin ωt

Load resistance

ωt

ωt

vo

vs

vo

(a) (b)

0

0

−

+ +

−

−

vs = Vm sin ωt

Figure 16.1.5Single-phase rectifier circuit with diodes.(a)Circuit diagram.(b)Voltage waveforms.

+

Thyristor T 1

Thyristor T 2

Ac

supply

R

Vm

Vm

−Vm

π

α

π 2 π

2 π

vs

vs = Vm sin ωt

Load resistance

ωt

ωt

vo

vs

vo

(a) (b)

0

0

−

+ +

−

−

α

vs = Vm sin ωt

Figure 16.1.6Single-phase ac–dc converter with two natural line-commutated thyristors.(a)Circuit

diagram.(b)Voltage waveforms.