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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
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Converter-fed DC Drive for a Separately-Excited Motor
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Waveform Summary Highly Inductive Load
Ripple-free Armature Current ECE 442 Power Electronics
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Principle of Power Control
The average armature voltage is The power supplied to the motor is ECE 442 Power Electronics
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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
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Principle of Power Control (continued)
To find the maximum peak-to-peak ripple current ECE 442 Power Electronics
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Application of a DC – DC Converter in Regenerative Braking
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Waveform Summary Armature Current Continuous and Ripple-Free
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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
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Principle of Regenerative Braking
The average voltage across the transistor is The regenerated power can be found from ECE 442 Power Electronics
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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
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Minimum Braking Speed Maximum Braking Speed ECE 442 Power Electronics
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For this example, the field and armature need to be in series
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Rheostatic Brake Control Dynamic Braking
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Waveform Summary ECE 442 Power Electronics
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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
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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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Combined Regenerative and Rheostatic Brake Control
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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
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Two-Quadrant DC–DC Converter Drive
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Quadrant Operation Summary
Regenerative Braking Control Power Control ECE 442 Power Electronics
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Power Control Q1 and D2 operate Q1 ON, Vs applied to the motor
Q1 turned OFF, D2 “free-wheels” Armature current decays ECE 442 Power Electronics
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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
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Four Quadrant DC-DC Converter Drive
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Quadrant Operation Summary
Forward Regeneration Forward Power Control Reverse Power Control Reverse Regeneration ECE 442 Power Electronics
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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
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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
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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
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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
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