Three Phase Separately Exited Drives

POWER ELECTRONICS(2150903)

PREET PATEL (151310109032)

Electrical Engineering Department

Contents...

• Three phase half wave converter

• Three phase semi controlled converter

• Three phase full controlled converter

• Features

• Limitations

• Applications

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:

𝐸𝑎 =3 3𝑉𝑚2𝜋

cos 𝛼 Where, (0 ≤ 𝛼 ≤ 𝜋)

Fig (1) 3-phase half wave converter based dc drive

+

_

3-Phase Converter

S1

S2

S3

R

Y

B

N

Field

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

VRBFreewheeling

VYRFreewheeling

VBYFreewheeling

𝐸𝑎 =3 3𝑉𝑚2𝜋

(cos 𝛼 + 1)

• Discontinuous mode Operation

Interval I II III IV V VI VII VIII IX

CONDUCTING

DEVICE S3D2 DFW NIL S1D3 DFW NILS2D1 DFW NIL

MODE Freewheeling Coasting Freewheeling Coasting Freewheeling

LOAD

VOLTAGEVBY 0 Eg VRB 0 Eg VRY 0 Eg

Ra

La

If

S1 S2 S3

D3D2D1

FWD

+

_

RYB Va

IO

+ _

Fig. (2) 3-phase semi- wave converter based dc drive

Wave form

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:

𝐸𝑎 =3 3𝑉𝑚𝜋

cos 𝛼 Where, (0 ≤ 𝛼 ≤ 𝜋)

Ra

La

If

S1 S3 S5

S2S6S4

+

_

RYB Va

+ _

Fig. (3) 3-phase full wave converter based dc drive

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.

LIMITATIONS

• Complex control circuit are required for 3 phase converters .

• The circuit are very costly and bulky.

APPLICATIONS

• High power dc motor drives.

• Traction drives.

• High power conveyer belts an lifts.

THANK YOU

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