CONVERTER FED DC MOTOR
DRIVE
Dr.P.Subha Karuvelam
Professor (CAS)/EEE
GCE, Tirunelveli

Content
• Steady state analysis of the single and three
phase converter fed separately excited DC
motor drive for continuous conduction
• Time ratio and current limit control
• 4 quadrant operation of converter / chopper
fed drive
• Applications

Single Phase fully controlled rectifier
fed DCM

Single Phase fully controlled rectifier
fed DCM

Single Phase fully controlled rectifier
fed DCM
1. When T1 & T3 conducts,
when T2& T4 conducts,
2. When biasing of thyristor depends on
when biasing of thyristor depends on
3.

Single Phase fully controlled rectifier
fed DCM
 is obtained by
 is obtained by speed reversal (IV quadrant)
 is obtained by
 Field current reversal (II quadrant)
 Armature current reversal (II quadrant)

Single Phase fully controlled rectifier
fed DCM
4. Rate of change of armature current

Single Phase fully controlled rectifier fed DCM
1. Duty Interval
Any one pair of Thyristor is ON
when T1 & T3 conducts,
when T2 & T4 conducts,
2. Zero Current Interval

Single Phase fully controlled rectifier fed DCM
 Motoring Mode
 Mode – I, II, III & IV
 Regeneration Mode
 Mode – V, VI & VII
 Continuous Current Mode
 Mode I & V
 Dis-continuous Current Mode
 Mode II,III,IV,VI & VII

Mode I – Motoring Mode

Mode I – Motoring Mode
For interval T1& T3 conducts
• When
Energy supplied by = Energy consumed by
• When
Energy consumed by = Energy supplied by
• When is negative
Energy consumed by = Energy supplied by

Mode I – Motoring Mode
• Duty Interval
when T1 & T3 conducts
when T2 & T4 conducts

Mode I – Transient Analysis
In interval T1 & T3 conducts
The Current is due to
 AC source is
 Back EMF is
 Transient component is

Mode I – Transient Analysis
• Where
• In steady state

Mode I – Steady State Analysis
• Motor Torque is
• Ave. Terminal voltage = Ave VD in +
Ave VD in + Back EMF
Average Terminal Voltage

Mode I – Steady State Analysis
• Average voltage drop in Ra
Average voltage drop across La

Mode V – Regeneration Mode
Motoring Regeneration

Mode V – Regeneration Mode
 is obtained by
 is obtained by speed reversal (IV quadrant)
 is obtained by
 Field current reversal (II quadrant)
 Armature current reversal (II quadrant)

Mode V – Regeneration Mode

Speed – Torque Characteristics
• For firing angle
• For firing angle

Speed – Torque Characteristics

Three Phase full converter fed DCM

Three Phase fully converter fed DCM
• Line voltage VAB is taken as reference
• Motoring mode – I & II
• Regeneration Mode – III &IV
• Continuous Current mode – I & III
• Dis-continuous Current mode – II & IV

Three Phase Voltage

Phase voltage and Line voltage

Conduction Interval
For  = 0
Thyristor Conduction
Period
T1 60 - 180
T2 120 - 240
T3 180 - 300
T4 240 - 360
T5 300 - 60
T6 0 - 120
For  = 30
Thyristor Conduction
Period
T1 90 - 210
T2 150 - 270
T3 210 - 330
T4 270 - 30
T5 330 - 90
T6 30 - 150

Conduction Interval
For  = 60
Thyristor Conduction
Period
T1 120 - 240
T2 180 - 300
T3 240 - 360
T4 300 - 60
T5 0 - 120
T6 60 - 180
For  = 90
Thyristor Conduction
Period
T1 150 - 270
T2 210 - 330
T3 270 - 30
T4 330 - 90
T5 30 - 150
T6 90 - 210

Conduction Interval
For  = 120
Thyristor Conduction
Period
T1 180 - 300
T2 240 - 360
T3 300 - 60
T4 0 - 120
T5 60 - 180
T6 120 - 240
For  = 180
Thyristor Conduction
Period
T1 240 - 360
T2 300 - 60
T3 0 - 120
T4 60 - 180
T5 120 - 240
T6 180 - 300

Mode I – Motoring mode

Mode I – Motoring mode
• For Duty interval

Mode I – Motoring mode

Mode III – Regeneration Mode

Mode III – Regeneration Mode
 is obtained by
 is obtained by speed reversal (IV quadrant)
 is obtained by
 Field current reversal (II quadrant)
 Armature current reversal (II quadrant)

Speed – Torque Characteristics
 When
No load operation is obtained
 When
No load operation is obtained

Speed – Torque Characteristics

4 quadrant operation of DCM

4 quadrant operation of converter fed
drive
 Armature Current Reversal
Single Phase full wave rectifier with
Reversing switch RS
Dual Converter
 Field Current Reversal
Single Phase full wave rectifier with
Reversing switch RS
Dual Converter

Armature Current Reversal
Single Phase full wave rectifier with RS

Single Phase full wave rectifier with RS
 Positive Armature Current – I & IV quadrant
 Negative Armature Current – II & III quadrant
• Procedure for speed reversal
Firing angle increased to highest value
Armature current reduces
Zero armature current is sensed
Dead time of 2 – 10ms
Armature is reversed by RS
Firing angle is reduced hence armature
current increases

Single Phase full wave rectifier with RS
 Drawbacks
 Slow response
 Contactor reversal time is 50-100ms
 Need a accurate zero current sensor
 Frequent maintenance due moving contact
 Advantage
 Low cost

Dual Converter
Non-simultaneous control Simultaneous control

Non-simultaneous control
• Only one rectifier operates at a time (I & IV )
• Procedure for speed reversal
Firing angle 1 increased to highest value
Armature current reduces
Zero armature current is sensed
Dead time of 2 – 10ms
Firing pulses are withdrawn from rectifier1
Firing pulses are given to rectifier 2
Armature current increases

Non-simultaneous control
• EMF matching method
 2 is set to make
 Armature current increases
 Restricted to rated value in current limiter
 Maximum (negative) torque developed by
motor
 Fast response

Simultaneous control
• Two converters are controlled simultaneously
• One converter – Rectifier
• Other converter – Inverter
• Instantaneous voltages are not equal

Simultaneous control
• In quadrant I,
Converter 1 in rectification with
Converter 2 in inversion with
• Procedure for speed reversal
 1 is increased and 2 is decreased
 Armature current shifts to rectifier 2
 Zero speed is reached when
 2 is reduced below 90 & 1 in increased
above 90

Simultaneous control

Simultaneous control
• Advantages
 Control is simple
 Continuous current conduction
 Good Speed regulation
• Disadvantages
 Presence of inductor increases cost, size,
weight
 Poor transient response
 Low PF and Efficiency

Field Current Reversal
Reversible Switch Dual Converter

Field Current Reversal
 Positive Field Current – I & IV quadrant
 Negative Field Current – II & III quadrant
 Field current is very small, rectifier rating also
small
 Larger field time constant, larger field current
reversal time