Wiwiet Yuniarto
DC drives fundamentals
© ABB Group March 17, 2014 | Slide 1
DC drives fundamentals General Layout General layout
MV line MV / LV transformer
§
Armature circuit
Field fuses (F3)
AC fuses (F1) Main contactor (K1)
Autotransformer (T3)
Commutation chokes (L1)
Field contactor (K3) Field converter
~ -
~ -
Armature converter DC fuses
Field winding © ABB Group March 17, 2014 | Slide 2
MV / LV transformer
M
Load
§
AC fuses
§
Main contactor
§
Commutation chokes
§
Armature converter
§
DC fuses
Field circuit §
Field fuses
§
Autotransformer
§
Field contactor
§
Field converter
DC drives fundamentals 6-pulse thyristor bridge (line commutated) DC current
AC line current
1
3 ~ AC network
L
~ L
N
~ L
~
1
© ABB Group March 17, 2014 | Slide 3
5
iL
2
3
Uda uL
4 §
3
Id
Controlled voltage source depending on firing angle a
6 §
2
Output voltage can be positive or negative
DC drives fundamentals Generating output voltage Voltages L1 L3 L1 L2 L3 a=0
§
Phase voltage (L1, L2, L3)
§
Phase to phase voltage (L12)
§
Thyristor 1 and 6 are active
§
The output is shown in red
L2 a=0 L12
AC line current 1
3 ~ AC network
~ ~ ~
L1
5
L2 L3
Id
iL Ud a uL
4 © ABB Group March 17, 2014 | Slide 4
3
DC current
6
2 DC voltage ( controlled)
DC drives fundamentals How a thyristor converter works
L1 L3 L2 a=0
§
6-pulse thyristor bridge with load
§
Firing sequence §
Thyristor 1 + 6
§
Thyristor 2 + 1
§
Thyristor 3 + 2
§
Thyristor 4 + 3
§
Thyristor 5 + 4
§
Thyristor 6 + 5
Id 1
3 ~ AC network
~ ~ ~
L1
5
iL
L2 L3
Ud a uL
4 © ABB Group March 17, 2014 | Slide 5
3
6
2
DC drives fundamentals Machine is motoring Positive voltage §
Firing angle a < 90°
§
Minimum firing angle a is 15° L1 L3 L2 a=0 L12
a = 30°
© ABB Group March 17, 2014 | Slide 6
§
Natural firing angle is the intersection between two phases
§
In this example the thyristor is fired after 30° (a = 30°) from natural firing angle
DC drives fundamentals Machine is generating (regenerative mode) Negative voltage §
Firing angle a > 90°
§
Maximum firing angle a is 150° L1 L3 L2 a=0 L12
a = 150° © ABB Group March 17, 2014 | Slide 7
DC drives fundamentals Shoot-through or commutation failure WECHSELRICHTERKIPPEN
§
Ausgangsgleichspannung U
DC drives can be compromised by commutation failures causing §
Damage fuses
§
Damage thyristors
da
§
t
a = 180°
L2
L3
L1
§ Mains Netzspannung t
a 0°
30° 60° 90° 120° 150° 180°
© ABB Group March 17, 2014 | Slide 8
Zündwinkel a
§
Causes of commutation failures §
Mains failure
§
Too large firing angles a
Working range has to be limited Typical firing angles a are between 15° and 150°
DC drives fundamentals Shoot-through or commutation failure
© ABB Group March 17, 2014 | Slide 9
§
Commutation failure begins near firing angles of 180°, so typically the firing angles are limited between 15° and 150°
§
Commutation fault are more likely with 4-Q drives compared to 2-Q drives. In 2-Q drives the condition will merely cause a loss in output voltage. In 4-Q drives, however, a severe overcurrent will occur. Commutation failure will cause very high current flow through motor, DC-breaker (if present), thyristors and fuses. It can cause damage to the motor, thyristors and fuses.
§
Commutation failures usually happens while regenerating. The common causes are: §
Loss of mains or a mains power dip
§
Poor mains quality (too soft mains and thus wide commutation notches)
§
Excessive armature voltage
§
Failure or malfunction of a firing pulse circuit
DC drives fundamentals Current in a DC drive Id
0°
60°
120°
180°
240°
300°
360°
§
DC current Id
§
DC current in a branch (120° width) IV2, IV3, IV4
§
AC current in mains (120° = | Id | and 60° = 0) IL1, IL2, IL3
wt
IV 2
IV 3
IV 4
I L1
I L2
I L3
© ABB Group March 17, 2014 | Slide 10
DC drives fundamentals Armature voltage of 2-quadrant drive For a 2-Q drive is valid §
Firing angle between 15° and 150°
§
Maximum save DC voltage
U da = 0.9 ·1.35 ·U mains · cos (15°)
U da = 0.9 ·1.35 · 400V · cos (15°) = 470V Voltage source characteristic:
§
150° because of commutation (current) and recovery (thyristor)
§
15° because of safety, due to supply voltage jitter
§
0.9 safety factor for 10 % mains voltage drop
Ud Ud ~ cos a
a
Maximum firing angle
© ABB Group March 17, 2014 | Slide 11
DC drives fundamentals Armature voltage of 4-quadrant drive Positive voltage source characteristic: Ud Ud ~ cos a
For a 4-Q drive is valid §
Firing angle between 15° and 150°
§
Maximum save DC voltage
U da = 0.9 ·1.35 ·U mains · cos (150°)
a
U da = 0.9 ·1.35 · 400V · cos (150°) = 420V
Maximum firing angle
Negative voltage source characteristic:
§
150° because of commutation (current) and recovery (thyristor)
§
15° because of safety, due to supply voltage jitter
§
0.9 safety factor for 10 % mains voltage drop
Ud
a Ud ~ cos a Maximum firing angle
© ABB Group March 17, 2014 | Slide 12
DC drives fundamentals Continuous and discontinuous armature current
IA
Continuous Current
LA Uda
Uda ~ cos a RA EMK ~ n, IF
© ABB Group March 17, 2014 | Slide 13
Discontinuous Current
DC drives fundamentals Quadrants §
Y
II
I §
The convention for a Cartesian coordinate system is §
The 1st quadrant is on the top right
§
All other numbers follow counterclockwise
Thus follows:
X Quadrant
III
© ABB Group March 17, 2014 | Slide 14
I
II
III
IV
IV x-coordinate
>0 <0 <0 >0
y-coordinate
>0 >0 <0 <0
DC drives fundamentals Single bridge (2-Q) Speed (voltage)
Id II Active braking
I Driving
M Torque (current)
III Driving
IV Braking
Forward driving only, opposite speed direction is only possible if the motor is been turned externally! Negative current is not possible! Active braking is not possible! © ABB Group March 17, 2014 | Slide 15
Uda Typical applications §
Extruder
§
Mixer
§
Rod and bar mills
DC drives fundamentals Double bridge (4-Q) Speed (voltage)
Id II Active braking
I Driving
M Torque (current)
III Driving
IV Braking
Speed in both directions is possible! Negative current is possible! Active braking is possible!
© ABB Group March 17, 2014 | Slide 16
Uda Typical applications §
Ski lifts
§
Test rigs
§
Winder
§
For smooth and fast torque reversal
DC drives fundamentals Single bridge (2-Q) with field reversal Speed
Id II Active braking
I Driving
M Torque
III Driving
© ABB Group March 17, 2014 | Slide 17
IV Braking
Uda Typical applications §
Mixer
§
Propulsion
§
Slow changeover of torque
§
Less control performance
§
Useable if P > 500 kW
DC drives fundamentals Max generating (regenerative) voltage Speed (voltage) §
II Active braking
I Driving
§
Torque § (current)
III Driving
IV Braking
Maximum generating voltage
© ABB Group March 17, 2014 | Slide 18
§
There is a voltage limitation in quadrants II and IV The maximum firing angle a is limited to 150° since the thyristors need a recovery time β of 30° This reduces the motor voltage in a 4-Q drive 2-Q drives cannot be used for active braking (positive speed direction), thus the motor voltage can be higher
DC drives fundamentals Motor acceleration (positive speed direction) 1 2
Speed (voltage)
3 I
II 1 III
© ABB Group March 17, 2014 | Slide 19
IV
Speed (EMF)
2
3 t
Torque (current) Torque (current)
§
Example: Acceleration in positive direction
§
Quadrant I is used §
Step 1: breakaway torque
§
Step 2: driving, acceleration at current limit
§
Step 3: driving (constant speed)
t
DC drives fundamentals Motor deceleration Speed (voltage)
1
1 2 II
© ABB Group March 17, 2014 | Slide 20
3
Speed (EMF)
I
t
Torque (current)
3 III
2
IV
Torque (current)
§
Example: Deceleration to zero speed
§
Quadrants I and II are used §
Step 1: driving (constant speed)
§
Step 2: active breaking, deceleration at current limit
§
Step 3: zero speed, current is zero
t
DC drives fundamentals Motor acceleration (negative speed direction) Speed (voltage)
II
Speed (EMF)
I
2 III
2
3 t
Torque (current)
1 IV 3
© ABB Group March 17, 2014 | Slide 21
1
Torque (current)
§
Example: Acceleration in negative direction
§
Quadrant III is used §
Step 1: motor is switched-off
§
Step 2: driving, acceleration at current limit
§
Step 3: driving (constant speed)
t
DC drives fundamentals Armature Converter
Id 1
~
Xc
iL
3
5
ic
EMF Uda
~ uL
~ 4
Mains
2
Commutation Thyristor bridge chokes
© ABB Group March 17, 2014 | Slide 22
6
Load
DC drives fundamentals Purpose of commutation chokes
~
For di / dt limitation during commutation
§
Prevent interferences between converters connected to the same line and other upstream connected equipment
§
Each converter gets its own commutation choke!
§
When thyristor converters operate, the line voltage is short-circuited during commutation from one thyristor to the next. Line reactors are used to reduce the commutation spikes on the upstream supply.
§
Commutation chokes lease to a reduction of maximum available output voltage, due to its voltage drop
~
Load © ABB Group March 17, 2014 | Slide 23
§
DC drives fundamentals Configurations One commutation choke per drive §
M
uK = 1 % or 4 %
M
Dedicated transformer §
§
M © ABB Group March 17, 2014 | Slide 24
One transformer per drive, typically used for large drives uK = 1 % to 10 %
DC drives fundamentals Configurations Autotransformer §
Requires an additional commutation choke
§
uK = 1 % or 4 %
M
D7 converters §
Maximum two converters per transformer
Aux. voltage
§
M © ABB Group March 17, 2014 | Slide 25
M
uK = 1 % to 10 %
DC drives fundamentals Fusing of DC drives Fault in the electronics, application, semiconductors §
Wrong tuning of controllers
§
Wrong parameter settings
§
Defective Printed Circuit Boards (ageing)
§
Defective semiconductor (ageing)
Commutation failure §
Missing line voltage
Insulation failures
M
© ABB Group March 17, 2014 | Slide 26
§
Converter
§
Wiring
§
Motor
§
AC supply
DC drives fundamentals Fusing of DC drives Fuses protect against §
Explosion of semiconductors with the risk of fire
§
Damages of the motor (flash over)
§
Damages of semiconductors in the converter
Protection philosophy
© ABB Group March 17, 2014 | Slide 27
§
Size of the system (cost of investment)
§
Application (2-Q, 4-Q, mainly regenerative)
§
Acceptable downtime, availability of system
§
Risk the customer wants to take
§
Supply voltage conditions (stable networks)
§
DC fuses (2 of them) should be used for all regenerative (4-Q) drives to protect the motor in case of a fault during regeneration
DC drives fundamentals Fusing of DC drives Not according to standard
M
fire explosion motor semiconductor
Not according to standard no no no no
M
fire explosion motor semiconductor
no no yes no
M Standard fuse Semiconductor fuse
© ABB Group March 17, 2014 | Slide 28
yes no no no
M
Not according to standard
Not according to standard fire explosion motor semiconductor
fire explosion motor semiconductor
Recommendation for 2-Q drives
M
fire explosion motor semiconductor
yes yes (yes) yes
Recommendati0on for 4-Q drive yes no yes no
fire explosion motor semiconductor
M
yes yes yes yes
DC drives fundamentals Fuse dimensioning Rules
© ABB Group March 17, 2014 | Slide 29
§
Basic fuse dimensioning is done according to rated current and voltage
§
Dimensioning based on the A2s-value
§
Fuse must handle overload conditions
§
DC fuses must be rated for the same current and voltage as AC fuses (Þ AC fuses = DC fuses)
