Power Electronics

1. Three Phase Separately Exited Drives
POWER ELECTRONICS
(2150903)
PREET PATEL (151310109032)
Electrical Engineering Department

2. Contents...
• Three phase half wave converter
• Three phase semi controlled converter
• Three phase full controlled converter
• Features
• Limitations
• Applications

3. 3 PHASE HALF WAVE CONVERTER BASED DC DRIVE
• A three phase half controlled converter fed from dc drive can operate in first quadrant. The
dc motor acts as RLE load.
• The ac-dc converter used for the field winding could be single phase or three phase semi-
converter.
• The operation is same as half wave controlled rectifier with RL load if the armature current
is continuous.
• The average armature voltage is given by:
𝐸 𝑎 =
3 3𝑉𝑚
2𝜋
cos 𝛼 Where, (0 ≤ 𝛼 ≤ 𝜋)

4. Fig (1) 3-phase half wave converter based dc drive
+
_
3-Phase
Converter
S1
S2
S3
R
Y
B
N
Field

6. 3-PHASE SEMI-WAVE CONVERTER BASED DC DRIVE
• RLE load is nothing but the DC motor load.
• The conducting device during six different intervals are shown in the table.
• The average armature voltage is given by:
Interval I II III IV V VI
CONDUCTING
DEVICE
S1D3 DFW S2D1 DFW S3D2 DFW
LOAD
VOLTAGE
VRB
Freewheelin
g
VYR
Freewheelin
g
VBY
Freewheelin
g
𝐸 𝑎 =
3 3𝑉𝑚
2𝜋
(cos 𝛼 + 1)

7. • Discontinuous mode Operation
Interval I II III IV V VI VII VIII IX
CONDUCTING
DEVICE S3D2 DFW NIL S1D3 DFW NIL
S2D1 DFW
NIL
MODE Freewheeling Coasting Freewheeling Coasting Freewheeling
LOAD
VOLTAGE
VBY 0 Eg VRB 0 Eg VRY 0 Eg

8. Ra
La
If
S1 S2 S3
D3D2
D1
FWD
+
_
R
Y
B Va
IO
+ _
Fig. (2) 3-phase semi- wave converter based dc drive

9. Wave form

10. 3 PHASE FULL WAVE CONVERTER BASED DC DRIVE
• The power circuit for three phase full converter feeding with separately excited load dc
motor.
• Since the thyristor is triggered at faster rate, as compared to that in single phase, the
armature current is mostly continuous.
• The circuit is similar to semi wave converter, the difference is just that freewheeling diode is
not present in this case.
• The average armature voltage is given by:
𝐸 𝑎 =
3 3𝑉𝑚
𝜋
cos 𝛼 Where, (0 ≤ 𝛼 ≤ 𝜋)

11. Ra
La
If
S1 S3 S5
S2S6
S4
+
_
R
Y
B Va
+ _
Fig. (3) 3-phase full wave converter based dc drive

13. FEATURE AND ADVANTAGES
1. High capacity motors can be driven with the help of three phase drive ( up to 5000 hp )
2. 3 phase drive does not heat the motors, since ripple frequencies are very high
3. Chances of discontinues armature current are reduce
4. Motor performance is improve in terms of regulation, dynamic response, torque speed characteristic
etc.

14. LIMITATIONS
• Complex control circuit are required for 3 phase converters .
• The circuit are very costly and bulky.

15. APPLICATIONS
• High power dc motor drives.
• Traction drives.
• High power conveyer belts an lifts.

16. THANK YOU
16