If not gated, R=? in case -VRRM < VAK < VRRM

1

• If not gated, R? in case -VRRM lt VAK lt VRRM
• If VAK gt 0 and gated (VGK 25 V) it starts
  conducting (R0) and stays so even if the gate
  voltage disappears (latch)
• Once in conduction it turns automatically off (no
  command)
• If reverse biased (VAK lt0)
• If the current reaches zero (IK 0) for more
  than tq

Vs
Vload
?Firing angle
Firing angle for a diode rectifier 0180?
(single phase) 30150? (3-phase)
2
Armature winding of DC motors for 4-quadrant
operation (elevators)
? 30?
?
T1
T3
T5
?
Vx
T6
T4
T2
Vy
?
Vxy
ia
3
Volt-time area loss due to the firing delay ?
Adjustable
Loss of mean voltage from Vx
Loss from Vxy
Ideal diode rectifier
4
Voltage drop due to overlap is the same as in the
3-phase diode rectifier
Calculation of ?
Easiest way to find it is by considering the
following loop
VBA
Area 2 Id h
?
?

• During this time, Vba causes the change of
• ia from Id to 0
• ib from 0 to Id

? ?
5
Line Current Waveforms
Id
? 30
120
-Id
T/2
0
T
Exactly the same waveform as for the diode
rectifier but displaced by ?
gt Id
(peak)
RMS input current
Displacement factor DPF cos (?)
Distortion factor DF
Power factor
PF is very poor at low output voltage ? near 90?