ABB GroupMarch 17, 2014 | Slide 1
DC drives fundamentalsWiwiet Yuniarto
ABB GroupMarch 17, 2014 | Slide 2
DC drives fundamentalsGeneral Layout
General layout MV / LV transformerArmature circuit AC fuses Main contactor Commutation chokes Armature converter DC fusesField circuit Field fuses Autotransformer Field contactor Field converter
~~--
Load
MV lineMV / LVtransformer
Main contactor(K1)
AC fuses(F1)
Commutationchokes (L1)
Field fuses(F3)
Armatureconverter
DC fuses
Fieldwinding
Field contactor(K3)
Fieldconverter
Autotransformer(T3)
M
ABB GroupMarch 17, 2014 | Slide 3
DC drives fundamentals6-pulse thyristor bridge (line commutated)
DC currentAC line current
3 ~ AC network 1 3 5
4 6 2
Uda
Id
iLL 1
uL
~
~
~L 3
L 2N
Controlled voltage sourcedepending on firing angle a
Output voltage can bepositive or negative
ABB GroupMarch 17, 2014 | Slide 4
L1L3L2a=0
L1L3L2a=0
L1L3L2a=0L12
3~ AC network
DC voltage(controlled)
DC currentAC line current
1 3 5
4 6 2
aUd
Id
iLL 1
uL
~
~
~L 3
L 2
Voltages
Phase voltage (L1, L2, L3)
Phase to phase voltage(L12)
Thyristor 1 and 6 are active
The output is shown in red
DC drives fundamentalsGenerating output voltage
ABB GroupMarch 17, 2014 | Slide 5
6-pulse thyristor bridge withload
Firing sequence
Thyristor 1 + 6
Thyristor 2 + 1
Thyristor 3 + 2
Thyristor 4 + 3
Thyristor 5 + 4
Thyristor 6 + 5
L1L3L2a=0
3~ AC network 1 3 5
4 6 2
aUd
Id
iLL 1
uL
~
~
~L 3
L2
DC drives fundamentalsHow a thyristor converter works
ABB GroupMarch 17, 2014 | Slide 6
DC drives fundamentalsMachine is motoring
L1L3L2a=0L12
a = 30
Positive voltage
Firing angle a < 90 Minimum firing angle a is 15
Natural firing angle is theintersection between twophases
In this example the thyristor isfired after 30 (a = 30) fromnatural firing angle
ABB GroupMarch 17, 2014 | Slide 7
DC drives fundamentalsMachine is generating (regenerative mode)
Negative voltage
Firing angle a > 90 Maximum firing angle a is 150
L1L3L2a=0L12
a = 150
ABB GroupMarch 17, 2014 | Slide 8
DC drives fundamentalsShoot-through or commutation failure
DC drives can be compromised bycommutation failures causing
Damage fuses
Damage thyristors
Causes of commutation failures
Mains failure
Too large firing angles a Working range has to be limited
Typical firing angles a are between 15and 150
0 30 60 90 120 150 180a
L2 L3 L1
a = 180
Ausgangsgleichspannung
Netzspannung
Zndwinkel
WECHSELRICHTERKIPPEN
t
t
Uda
a
Mains
ABB GroupMarch 17, 2014 | Slide 9
DC drives fundamentalsShoot-through or commutation failure
Commutation failure begins near firing angles of 180, so typically thefiring angles are limited between 15 and 150
Commutation fault are more likely with 4-Q drives compared to 2-Qdrives. In 2-Q drives the condition will merely cause a loss in outputvoltage. 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 tothe motor, thyristors and fuses.
Commutation failures usually happens while regenerating. The commoncauses 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
ABB GroupMarch 17, 2014 | Slide 10
DC drives fundamentalsCurrent in a DC drive
DC currentId
DC current in a branch(120 width)IV2, IV3, IV4
AC current in mains(120 = | Id | and 60 = 0)IL1, IL2, IL3
dI
60 120 240 300 3601800 tw2VI
3VI
4VI
1LI
2LI
3LI
ABB GroupMarch 17, 2014 | Slide 11
DC drives fundamentalsArmature voltage of 2-quadrant drive
For a 2-Q drive is valid
Firing angle between 15 and 150
Maximum save DC voltage
150 because of commutation (current)and recovery (thyristor)
15 because of safety, due to supplyvoltage jitter
0.9 safety factor for 10 % mains voltagedrop
Voltage source characteristic:Ud
a
Ud ~ cos a
Maximum firing angle
VVU d 470)15(cos40035.19.0 ==a
)15(cos35.19.0 = mainsd UU a
ABB GroupMarch 17, 2014 | Slide 12
DC drives fundamentalsArmature voltage of 4-quadrant drive
For a 4-Q drive is valid
Firing angle between 15 and 150
Maximum save DC voltage
150 because of commutation (current)and recovery (thyristor)
15 because of safety, due to supplyvoltage jitter
0.9 safety factor for 10 % mains voltagedrop
Positive voltage source characteristic:Ud
a
Ud ~ cos a
Maximum firing angle
Negative voltage source characteristic:Ud
aUd ~ cos a
Maximum firing angle
VVUd 420)150(cos40035.19.0 ==a
)150(cos35.19.0 = mainsd UU a
ABB GroupMarch 17, 2014 | Slide 13
DC drives fundamentalsContinuous and discontinuous armature current
ContinuousCurrent
DiscontinuousCurrent
Uda
LA
RA
EMK~ n, IF
Uda~ cos a
IA
ABB GroupMarch 17, 2014 | Slide 14
DC drives fundamentalsQuadrants
The convention for a Cartesiancoordinate system is
The 1st quadrant is on the top right
All other numbers followcounterclockwise
Thus follows:
Quadrant I II III IV
x-coordinate > 0 < 0 < 0 > 0
y-coordinate > 0 > 0 < 0 < 0
II I
III IV
Y
X
ABB GroupMarch 17, 2014 | Slide 15
DC drives fundamentalsSingle bridge (2-Q)
Typical applications
Extruder
Mixer
Rod and bar mills
IIActive braking
IDriving
IIIDriving
IVBraking
Speed (voltage)
Torque(current)
M
Uda
Id
Forward driving only, opposite speed direction isonly possible if the motor is been turnedexternally!Negative current is not possible!Active braking is not possible!
ABB GroupMarch 17, 2014 | Slide 16
DC drives fundamentalsDouble bridge (4-Q)
Typical applications
Ski lifts
Test rigs
Winder
For smooth and fast torque reversal
IIActive braking
IDriving
IIIDriving
IVBraking
Speed (voltage)
Torque(current)
M
Uda
Id
Speed in both directions is possible!Negative current is possible!Active braking is possible!
ABB GroupMarch 17, 2014 | Slide 17
DC drives fundamentalsSingle bridge (2-Q) with field reversal
M
Uda
IdII
Active brakingI
Driving
IIIDriving
IVBraking
Speed
Torque
Typical applications
Mixer
Propulsion
Slow changeover of torque
Less control performance
Useable if P > 500 kW
ABB GroupMarch 17, 2014 | Slide 18
DC drives fundamentalsMax generating (regenerative) voltage
There is a voltage limitation inquadrants II and IV
The maximum firing angle a is limited to150 since the thyristors need arecovery time of 30
This reduces the motor voltage in a 4-Qdrive
2-Q drives cannot be used for activebraking (positive speed direction), thusthe motor voltage can be higher
Maximumgenerating voltage
IIActive braking
IDriving
IIIDriving
IVBraking
Speed (voltage)
Torque(current)
ABB GroupMarch 17, 2014 | Slide 19
DC drives fundamentalsMotor acceleration (positive speed direction)
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)
Torque(current)
Speed (voltage)
21
3
IVIII
II I tSpeed(EMF)
1 2 3
tTorque
(current)
ABB GroupMarch 17, 2014 | Slide 20
DC drives fundamentalsMotor deceleration
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
1 2 3
t
21
3
IVIII
II ITorque
(current)
Speed (voltage)
Speed(EMF)
Torque(current)
ABB GroupMarch 17, 2014 | Slide 21
DC drives fundamentalsMotor acceleration (negative speed direction)
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)
2
1
3IVIII
II I t
1 2 3
t
Torque(current)
Speed (voltage)
Speed(EMF)
Torque(current)
ABB GroupMarch 17, 2014 | Slide 22
DC drives fundamentalsArmature Converter
Mains Commutation
chokes
Thyristor bridge Load
1 3 5
4 6 2
icEMF
aUd
Id
iLXc
uL
~
~
~
ABB GroupMarch 17, 2014 | Slide 23
DC drives fundamentalsPurpose of commutation chokes
For di / dt limitation during commutation
Prevent interferences between converters connected tothe same line and other upstream connected equipment
Each converter gets its own commutation choke!
When thyristor converters operate, the line voltage isshort-circuited during commutation from one thyristor tothe next. Line reactors are used to reduce thecommutation spikes on the upstream supply.
Commutation chokes lease to a reduction of maximumavailable output voltage, due to its voltage drop
~~
Load
ABB GroupMarch 17, 2014 | Slide 24
DC drives fundamentalsConfigurations
One commutation choke per drive
uK = 1 % or 4 %
Dedicated transformer
One transformer per drive, typicallyused for large drives
uK = 1 % to 10 %
M M
M
ABB GroupMarch 17, 2014 | Slide 25
DC drives fundamentalsConfigurations
Autotransformer
Requires an additional commutationchoke
uK = 1 % or 4 %
D7 converters
Maximum two converters pertransformer
uK = 1 % to 10 %
M
M M
Aux. voltage
ABB GroupMarch 17, 2014 | Slide 26
DC drives fundamentalsFusing 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
Converter
Wiring
Motor
AC supply
MM
ABB GroupMarch 17, 2014 | Slide 27
DC drives fundamentalsFusing 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
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 toprotect the motor in case of a fault during regeneration
ABB GroupMarch 17, 2014 | Slide 28
DC drives fundamentalsFusing of DC drives
Not accordingto standard
fire yesexplosion nomotor yessemiconductor no
M
Recommendati0onfor 4-Q drive
fire yesexplosion yesmotor yessemiconductor yes
M
Not accordingto standard
fire noexplosion nomotor yessemiconductor no
M
Not accordingto standard
fire noexplosion nomotor nosemiconductor noM
Recommendationfor 2-Q drives
fire yesexplosion yesmotor (yes)semiconductor yesM
Not accordingto standard
fire yesexplosion nomotor nosemiconductor noM
Standard fuse
Semiconductor fuse
ABB GroupMarch 17, 2014 | Slide 29
DC drives fundamentalsFuse dimensioning
Rules
Basic fuse dimensioning is doneaccording to rated current and voltage
Dimensioning based on the A2s-value
Fuse must handle overload conditions
DC fuses must be rated for the samecurrent and voltage as AC fuses ( ACfuses = DC fuses)