1) A chopper is used to provide variable DC voltage from a constant DC source and is widely used to control DC motors. 2) A chopper-fed DC drive works by connecting a DC chopper between a fixed-voltage DC source and DC motor to vary the armature voltage. 3) A multi-quadrant chopper drive can provide forward power control, forward regeneration, reverse power control, and reverse regeneration by controlling the switching of the thyristors in the chopper circuit.

1. MULTIQUADRANT CONTROL OF
CHOPPER-FED DC MOTORS
Institute of Industrial Electronics Engineering-Karachi
Presentation by
Muhammad Ahsan Ali (1915)

2. CHOPPER
• Chopper is a static device.
• A variable dc voltage is obtained from a constant dc
voltage source.
• Also known as dc-to-dc converter.
• Widely used for motor control.
• Also used in regenerative braking.
• Thyristor converter offers greater efficiency, faster
response, lower maintenance, smaller size and smooth
control.

3. CHOPPER FED DC DRIVES
• A dc chopper is connected between a fixed-voltage dc
source and dc motor to vary the armature voltage.
• A chopper is a high speed on/off semiconductor switch
which connects source to load and disconnects the load
from source at a fast speed.
• Choppers are used to get variable dc voltage from a dc
source of fixed voltage.
• Chopper circuits are used to control both separately
excited and Series circuits.

4. ADVANTAGES OF CHOPPER CIRCUITS
• Ripple content in the output is small.
• Peak/average and rms/average current ratios are small.
• The chopper is supplied from a constant dc voltage using
batteries.
• Current drawn by the chopper is smaller than in phase
controlled converters.
• Chopper circuit is simple and can be modified to provide
regeneration and the control is also simple.

5. CONTROL MODES OF DC CHOPPER DRIVE
1. Power(or acceleration) control
2. Regenerative brake control
3. Rheostatic brake control
4. Combined Regenerative and Rheostatic Brake Control

6. POWER CONTROL

7. WAVEFORM SUMMARY
(Highly Inductive Load)
Ripple-free Armature Current
sa kVV 
asaao IkVIVP 
a
s
s
s
eq
kI
V
I
V
R 
m
m
m
s
fL
R
R
V
I
4
tanhmax 
Armature Voltage:
Power suplpied:
Input Resistance:
Peak-to-peak current:
where k =conduction duty cycle

8. REGENERATIVE BRAKE CONTROL

9. WAVEFORM SUMMARY

10. EQUATIONS
sch VkV )1( 
)1( kVIP sag 
amsg IRVkE  )(1
m
a
s
a
g
eq Rk
I
V
I
E
R  )1( max
max
min
min








fv
am
fv
s
fv
am
IK
IR
IK
V
IK
IR
Voltage across transistor:
Regenerated power:
Voltage when motor
acting as generator:
Equivalent load resistance:
Minimum Braking Speed:
Maximum Braking Speed:

11. RHEOSTATIC BRAKE CONTROL

12. WAVEFORM SUMMARY

13. EQUATIONS
• The average current in the braking resistor is
• The average voltage across the braking resistor is
)1( kII ab 
)1( kIRV abb 
• The equivalent load resistance of the generator
• The power dissipated in the resistor Rb is
mb
a
b
eq RkR
I
V
R  )1(
)1(2
kRIP bab 

14. COMBINED REGENERATIVE AND
RHEOSTATIC BRAKE CONTROL

15. • Used when the supply is partly
“receptive”
• Remove regenerative braking if
line voltage is too high
– Turn thyristor TR on
– Divert current to RB
– Apply rheostatic braking
– TR is “self-commutated”
COMBINED REGENERATIVE AND
RHEOSTATIC BRAKE CONTROL (CONT.)

16. MULTIQUADRANT CHOPPER DRIVES
o Forward Power Control (I-Quadrant)
o Forward Regeneration (II-Quadrant)
o Reverse Power Control (III-Quadrant)
o Reverse Regeneration (IV-Quadrant)
• Control Modes

17. Forward Power Control
Q1
T1 & T4 is ON
Current Flow : VS
+ _ T1 _Motor_T4_VS
-
Current Ia & Va are positive
Operates in First Quadrant

18. T1 is OFF & T4 is ON. Inductor current has to flow in the same Direction.
Diode D1 is FB
Inductor Current freewheels through D1 & T4
Output Voltage is Zero
Forward Power Control (cont.)

19. T4 is OFF. T2 is ON. (Load is not connected with the source).
Back Emf drives the current through T2 & D3
Forward Power Control (cont.)

20. Q2
T2 is OFF. Diode D2 is FB
Current flows through D3 & D1
 Current Ia is negative & Va is positive.
Operates in second quadrant.
FORWARD REGENERATION

21. Q3
T3 & T2 is ON
Current Flow : Vdc
+ _ T3 _Motor_T2_Vdc
-
Current Ia & Va are negative
Operates in third Quadrant
Reverse Power Control

22. Q4
T4 IS Turned Off, D4 is FB
Current Flows through Va+ - D1 – D4 – Va-
Va is negative. But current Ia is positive
Operates in fourth quadrant
REVERSE REGENERATION

23. References
• Power Electronics: Circuit Devices and Application By Haroon Rashid
• Digital Power Electronics and Applications By Ling Luo, M. Rashid

24. THANK YOU