1. DC-DC Converter Drives
Principle of Power Control
Principle of Regenerative Brake Control
Principle of Rheostatic Brake Control
Combined Regenerative and Rheostatic Brake Control
Two and Four Quadrant DC – DC Converter Drives
ECE 442 Power Electronics

2. Converter-fed DC Drive for a Separately-Excited Motor
ECE 442 Power Electronics

3. Waveform Summary Highly Inductive Load
Ripple-free Armature Current
ECE 442 Power Electronics

4. Principle of Power Control
The average armature voltage is
The power supplied to the motor is
ECE 442 Power Electronics

5. Principle of Power Control (continued)
The average value of the input current is
The equivalent input resistance seen by the source is
Control Power Flow by adjusting the duty cycle
ECE 442 Power Electronics

6. Principle of Power Control (continued)
To find the maximum peak-to-peak ripple current
ECE 442 Power Electronics

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10. Application of a DC – DC Converter in Regenerative Braking
ECE 442 Power Electronics

11. Waveform Summary Armature Current Continuous and Ripple-Free
ECE 442 Power Electronics

12. Regenerative Braking
Begin with the motor turning by kinetic energy of the vehicle
Armature current flows as shown
Turn the transistor on
Armature current rises
Turn the transistor off
Diode turns on, current flows into the supply
ECE 442 Power Electronics

13. Principle of Regenerative Braking
The average voltage across the transistor is
The regenerated power can be found from
ECE 442 Power Electronics

14. Principle of Regenerative Braking (continued)
The voltage generated by the motor acting as a generator is
The equivalent load resistance of the motor acting as a generator is
Control Power by changing k
ECE 442 Power Electronics

15. Minimum Braking Speed
Maximum Braking Speed
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16. For this example, the field and armature need to be in series
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19. Rheostatic Brake Control Dynamic Braking
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20. Waveform Summary
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21. Principle of Rheostatic Brake Control
The average current in the braking resistor is
The average voltage across the braking resistor is
ECE 442 Power Electronics

22. Principle of Rheostatic Brake Control (continued)
The equivalent load resistance of the generator
The power dissipated in the resistor Rb is
ECE 442 Power Electronics

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26. Combined Regenerative and Rheostatic Brake Control
ECE 442 Power Electronics

27. Combined Regenerative and Rheostatic Brake Control (continued)
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”
ECE 442 Power Electronics

28. Two-Quadrant DC–DC Converter Drive
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29. Quadrant Operation Summary
Regenerative Braking Control Power Control
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30. Power Control Q1 and D2 operate Q1 ON, Vs applied to the motor
Q1 turned OFF, D2 “free-wheels”
Armature current decays
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31. Regenerative Control Q2 and D1 operate
Q2 turned ON, motor acts as a generator, and the armature current rises
Q2 turned OFF, motor returns energy to the supply via D1 “free-wheeling”
ECE 442 Power Electronics

32. Four Quadrant DC-DC Converter Drive
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33. Quadrant Operation Summary
Forward Regeneration Forward Power Control
Reverse Power Control Reverse Regeneration
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34. Forward Power Control Q1 and Q2 turned ON
Supply voltage appears across the motor
Armature current rises
Q1 and Q2 turned OFF
Armature current decays via D3 and D4
ECE 442 Power Electronics

35. Forward Regeneration Q1, Q2, and Q3 turned OFF Turn Q4 ON
Armature current rises and flows through Q4, D2
Q4 turned OFF, motor acts as a generator, returns energy back to the supply via D1, D2
ia reverses
ECE 442 Power Electronics

36. Reverse Power Control Q3 and Q4 turned ON
Supply voltage appears in the reverse direction across the motor
Armature current rises and flows in the reverse direction
Q3 and Q4 turned OFF
Armature current decays via D1 and D2 ia
ECE 442 Power Electronics

37. Reverse Regeneration Q1, Q3, Q4 turned OFF Q2 turned ON
Armature current rises through Q2 and D4
Q2 turned OFF
Armature current falls and returns energy via D3 and D4
i a
ECE 442 Power Electronics