ece 442 power electronics1 controlled-rectifier fed drive armaturefield
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ECE 442 Power Electronics 1
Controlled-Rectifier Fed Drive
Armature Field
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ECE 442 Power Electronics 2
Chopper-Fed Drive
Armature Field
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ECE 442 Power Electronics 3
Equivalent Circuit of a Separately-Excited DC Motor
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ECE 442 Power Electronics 4
ff f f f
aa a a a g
g v f
d t f a
d L
div R i L
dtdi
v R i L edt
e K i
T K i i
dT J B T
dt
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ECE 442 Power Electronics 5
0
f f f
g v f
a a a g
a a a v f
d t f a
d L
d d
Steady state
d
dtV R I
E K I
V R I E
V R I K I
T K I I
T B T
P T
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ECE 442 Power Electronics 6
a a a v f
a a a a a a
v f fv
f
V R I K I
V I R V I R
K I VK
R
Solve for the motor speed
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ECE 442 Power Electronics 7
Control of the motor speed
• Control armature voltage, Va
– Voltage control
• Control the field current, If
– Current control
• Control the armature current, Ia
a a a
fv
f
V I R
VK
R
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ECE 442 Power Electronics 8
Magnetization Characteristic
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ECE 442 Power Electronics 9
Characteristics of Separately-Excited Motors
Rated speed
Use field-current control
Use armature voltage control
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ECE 442 Power Electronics 10
Equivalent circuit of a DC Series Motor
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ECE 442 Power Electronics 11
( )
( )
( )
g v a
a a f a g
a a f a v f
d t a f
d L
a a f a
v f
E K I
V R R I E
V R R I K I
T K I I
T B T
V R R I
K I
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ECE 442 Power Electronics 12
Controlling the Motor Speed
• Control the armature voltage, Va
• Control the armature current, Ia
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ECE 442 Power Electronics 13
Characteristics of DC Series motors
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ECE 442 Power Electronics 14
Operating Modes
• In variable-speed applications, a dc motor may be operating in one or more of the following “Modes”
• Motoring
• Regenerative braking
• Dynamic braking
• Plugging
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ECE 442 Power Electronics 15
Motoring Mode
“Back emf”, Eg is < supply voltage Va
Both Ia and If are positive
Developed torque meets load demand
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ECE 442 Power Electronics 16
Regenerative Braking Mode
Motor acts as a Generator
Eg becomes > supply Voltage Va
Ia becomes negative
Kinetic energy of the motor is returned to the supply
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ECE 442 Power Electronics 17
Dynamic Braking
Replace the supply voltage with a resistor
Power dissipated in the resistor rather than given back to the source
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ECE 442 Power Electronics 18
Plugging
Reverse the armature terminals while running
Va and Eg act in the same direction
Ia is reversed, producing “braking” torque
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ECE 442 Power Electronics 19
Four-Quadrant Operation
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ECE 442 Power Electronics 20
Single-Phase DC Drive
Change Va by changing firing angle Inductor Lm is a “smoothing” Inductor to prevent
discontinuous current
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ECE 442 Power Electronics 21
Armature Reversal
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ECE 442 Power Electronics 22
Field Reversal
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ECE 442 Power Electronics 23
Single-Phase Half-Wave Converter Drive
(1 cos )2
0
(1 cos )
0
ma a
a
mf f
f
VV
VV
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ECE 442 Power Electronics 24
Quadrant of Operation
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ECE 442 Power Electronics 25
Waveform Summary
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ECE 442 Power Electronics 26
Single-Phase Semiconverter Drives
(1 cos )
0
(1 cos )
0
ma a
a
mf f
f
VV
VV
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ECE 442 Power Electronics 27
Quadrant(s) of Operation
Semiconverter – one quadrant converter
One polarity of output voltage and current
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ECE 442 Power Electronics 28
Waveform Summary
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ECE 442 Power Electronics 29
Single-Phase Full-Converter Drives
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ECE 442 Power Electronics 30
Quadrant(s) of Operation
Full converter – two quadrant converter
Output voltage polarity can be positive or negative
Output current has one polarity
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ECE 442 Power Electronics 31
Waveform Summary
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ECE 442 Power Electronics 32
Single-Phase Dual-Converter Drives
Dual converter can operate in all four quadrants
Output voltage and current can be positive or negative