Obat Aborsi Surabaya 0851\7696\3835 Jual Obat Cytotec Di Surabaya
DC Drives WITH DC DC (1).ppt
1. DC – DC Converter Fed Drives
To obtain variable DC voltage from fixed DC source
Self-commutated devices preferred (MOSFETs, IGBTs,
GTOs) over thyristors
Commutated by lower power control signal
Commutation circuit not needed
Can be switched at higher frequency for same rating
Improved motor performance (less ripple, no discontinuous
currents, increased control bandwidth)
Suitable for high performance applications
Regenerative braking possible up to very low speeds even
when fed from fixed DC voltage source
1
2. Dr. Ungku Anisa, July 2008 EEEB283 - Electrical Machines & Drives 2
3. DC – DC Converter Fed Drives
- Step Down Class A Chopper
Motoring
3
T
Q1
Q2
Q3 Q4
4. DC – DC Converter Fed Drives
- Step Down Class A Chopper
S is ON (0 t ton)
4
Motoring
V
E
dt
di
L
i
R a
a
a
a
Duty
Interval
- ia
5. DC – DC Converter Fed Drives
- Step Down Class A Chopper
S if OFF (ton t T)
5
Motoring
0
E
dt
di
L
i
R a
a
a
a
Freewheeling
Interval
- ia
6. DC – DC Converter Fed
- Step Down Class A Chopper
Motoring
Duty cycle
Under steady-state conditions
Motor side:
Chopper side:
Hence,
6
period
chopper
where
T
T
t
k on
E
I
R
V
kV a
a
a
a
a
R
E
kV
I
kT
Freewheeling
Interval
- ia
Duty
Interval
- ia
E
I
R
V a
a
a
kV
Va
average Va
average Ia
7. DC – DC Converter Fed Drives
- Step Up Class B Chopper
Regenerative Braking
7
T
Q1
Q2
Q3 Q4
•Possible for speed
above rated speed
and down to nearly
zero speed
•Application:
• Battery operated
vehicles
• Regenerated
power stored in
battery
8. DC – DC Converter Fed Drives
- Step Up Class B Chopper
S is ON (0 t ton)
8
Regenerative
Braking
Energy Storage
Interval
- ia
Va = 0
ia increases due to E
Mechanical energy
converted to
electrical (i.e.
generator)
Energy stored in La
E
dt
di
L
i
R a
a
a
a
9. DC – DC Converter Fed Drives
- Step Up Class B Chopper
S if OFF (ton t T)
9
Regenerative
Braking
Duty
Interval
- ia
ia flows through diode
D and source V
Energy stored in La &
energy supplied by
machine are fed to
the source E
V
dt
di
L
i
R a
a
a
a
10. DC – DC Converter Fed Drives
- Step Up Class B Chopper
Regenerative Braking
Duty cycle
Under steady-state conditions
Generator side:
Chopper side:
Hence,
Dr. Ungku Anisa, July 2008 EEEB283 - Electrical Machines & Drives 10
period
chopper
where
T
T
t
k on
a
a
a I
R
E
V
V
k
1
a
a
R
V
k
E
I
1
T
Duty
Interval
- ia
Energy Storage
Interval
- ia
a
a
a I
R
E
V
V
k
Va
1
average Va
average Ia
11. DC – DC Converter Fed Drives
- Two-quadrant Control
Forward motoring Q1 - T1 and D2
Forward braking Q2 – T2 and D1
11
D2
+
Va
-
T1
D1
T2
D2
+
V
-
T
Q1
Q2
Q3 Q4
No Speed
Reversal
12. DC – DC Converter Fed Drives
- Two-quadrant Control
Forward motoring Q1
T1 conducting: Va = V
D2 conducting: Va = 0
Dr. Ungku Anisa, July 2008 EEEB283 - Electrical Machines & Drives 12
T
Q1
Q2
Q3 Q4
T1
T2
D1
+
Va
-
D2
ia
+
V
T1
T2
D1
+
Va
-
D2
ia
+
V
•Average Va positive
•Average Va made larger
than back emf Eb
•Ia positive
Va Eb
13. DC – DC Converter Fed Drives
- Two-quadrant Control
Forward braking Q2
D1 conducting: Va = V
T2 conducting: Va = 0
T
Q1
Q2
Q3 Q4
T1
T2
D1
+
Va
-
D2
ia
+
V
T1
T2
D1
+
Va
-
D2
ia
+
Vdc
Va
Eb
•Average Va positive
•Average Va made
smaller than back emf Eb
•Ia negative
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14. DC – DC Converter Fed Drives
- Four-quadrant Control
Operation in all quadrants
Speed can be reversed
+ Va -
T1
D1
T2
D2
D3
D4
T3
T4
T
Q1
Q2
Q3 Q4
14
15. DC – DC Converter Fed Drives
- Four-quadrant Control
Forward Motoring Q1
T1 and T2 on
Va = V
Ia increases
Reverse Braking Q4
(Regeneration)
T1 off but T2 still on
Va = 0
Ia decays thru T2 and D4
T1 and T2 off
Va = -V
Ia decays thru D3 and D4
Energy returned to supply
+ Va -
T1
D1
T2
D2
D3
D4
T3
T4
T
Q1
Q2
Q3 Q4
+
V
-
T3 and T4 off
15
16. DC – DC Converter Fed Drives
- Four-quadrant Control
Reverse Motoring Q3
T3 and T4 on
Va = -V
Ia increases in reverse direction
Forward Braking Q2
(Regeneration)
T3 off but T4 still on
Va = 0
Ia decays thru T4 and D2
T3 and T4 off
Va = V
Ia decays thru D1 and D2
Energy returned to supply
+ Va -
T1
D1
T2
D2
D3
D4
T3
T4
T
Q1
Q2
Q3 Q4
+
V
-
T1 and T2 off
16
17. Closed-loop Control
Feedback loops may be provided to satisfy one or more of the
following:
Protection
Enhancement of speed response
Improve steady-state accuracy
Variables to be controlled in drives:
Torque – achieved by controlling current
Speed
Position
Controllers are designed based on a linear averaged model
17
18. Closed-loop Control
Variables to be controlled in drives:
Torque – achieved by controlling current
Commonly employed current sensor:
Current shunt – no electrical isolation, cheap
Hall effect sensor – provides electrical isolation
Speed is governed by torque:
Dr. Ungku Anisa, July 2008 EEEB283 - Electrical Machines & Drives 18
dt
d
J
T
T L
e
firing
circuit
current
controller
controlled
rectifier
+
Va
–
vc
iref
+
-
e.g. With phase-controlled rectifier
19. Closed-loop Control
Variables to be controlled in drives:
Speed – with or without current loop
Commonly employed speed/position sensor:
Tachogenerator – analog based
Digital encoder – digital based, converts speed to pulses
Torque is governed by speed demand:
Without current loop: no limit on current – can be too high
With current loop: current can be limited
19
20. Closed-loop Control
Variables to be controlled in drives:
Speed control without current loop:
Simple implementation
Current can be too high may damage converter
20
Speed
controller
Power
Electronic
Converters
* +
-
+
va
vc
Tacho
21. Closed-loop Control
Variables to be controlled in drives:
Speed control with current loop:
Two controllers required: speed and current
Current limited by limiting ia*
21
Speed
controller
Power
Electronic
Converters
* +
-
+
va
vc
Tacho
Current
controller
ia*
ia
+
-
22. References
Rashid, M.H, Power Electronics: Circuit, Devices and
Applictions, 3rd ed., Pearson, New-Jersey, 2004.
Dubey, G.K., Fundamentals of Electric Drives, 2nd ed., Alpha
Science Int. Ltd., UK, 2001.
Krishnan, R., Electric Motor Drives: Modeling, Analysis and
Control, Prentice-Hall, New Jersey, 2001.
Nik Idris, N. R., Short Course Notes on Electrical Drives,
UNITEN/UTM, 2008.
Ahmad Azli, N., Short Course Notes on Electrical Drives,
UNITEN/UTM, 2008.
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