Download motors in parallel

Altivar 71 Output filters
Selection Guide
Producto y Versión:
ATV61/71
Revisión
Fecha
Autor
1.0
2.0
1/2011
3/2011
Sergio Núñez Núñez
Centro de Competencia Técnica
Modificaciones
Primera versión
Actualización diagrama de selección y contenido
ATV 71: Output filters Selection Guide
Summary
1. Selection Diagram
2. Causes of motor overvoltages
3. Multiplication factors
>
>
Switching frequency influences
Motors in parallel
4. Selection Table
5. Overvoltage and dv/dt limitation
options
>
>
>
SVL overvoltage limitation function
Motor Choke.
Sinus Filter
6. Adequation of the motor
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Output Filters Selection Diagram
1
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Output Filters Selection Diagram
2
5
4
6
3
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Causes of motor overvoltages
● The switching of the output voltage on the output of a drive by the IGBT bridge generates
rapid variations in voltage (dV/dt).
+ VDC bus
e.g. 400 * 2 = 566V
Drive output voltage (PWM)
dV/dt 2 to 10kV/µS
0V
Motor current
nearly sinusoidal
- VDC bus
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Causes of motor overvoltages
●
●
Overvoltages are generated by reflected waveforms due to dV/dt and to poor
impedance matching between the motor and the motor cable.
The amplitude and the dV/dt are principally functions of the cable length and the
modulation technique.
overvoltage
dV/dt
l cable
PWM Voltage at Motor Terminals
1500
Overvoltage at the motor terminals
Typically up to 2 x V bus DC
1000
+ Vdc
ex U main =400Vac
Motoring Quadrant
Û = 400xSQR2x2 = 1132V
Generating Quadrant (braking)
Û = 790x2 = 1580V
Voltage
500
- Vdc
0
-500
-1000
Sometimes in certain cases the
overvoltage can be greater than 2
Vdc ...
-1500
-2000
Tim e
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Causes of motor overvoltages
● Overvoltages and dV/dt can degrade the insulation of motor windings and cables.
● This problem is generally above than 400V and for motors not having insulation compatible with
variable speed drives (class F).
● Overvoltages can be destructive with cable lengths of 20 meters or above.
● The can be greater than 2Vdc in the case of PWM with short tmin (ex 2µS for 200m 4kW)
Remarks :
The dV/dt gradient is as bad for motor
windings as the overvoltage itself
(corona effect).
And very short wires can also be a
problem because of low inductance and
parasitic capacitance.
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Multiplication factors
● Factors to be taken into account:
● If parallel cables are used, the cable lenght to be considered must be
multiplied by 2,
● If motors are in parallel, the cable lenght to be considered must be the sum
of all motor cable lengthes.
● Note: a multiplication factor can be used if the swithching frequency used is
greater than the default value, but in this case, the use of output filter is
not allowed.
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Switching frequency influences
When using “SFR” parameter for example between 4 and 8 kHz the losses
increase by 1,3 in tri-phase modulation so it is necessary to dicrease the length of
motor cable.
Recommendation for length of motor cable in function of switching frequency. (1) These factors
are theorical values.
Note: a multiplication factor can be used if the swithching
frequency used is greater than the default value, but in this case,
the use of output filter is not allowed.
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Motors in parallel
• The cable length to be considered for choosing an output filter is the sum of all
the cable lengths (ex L1+L2+3L3).
• Minimize the cable length (drive as close as possible to the motors).
L1
L2
L3
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Selection table depending on cable length
Output filter recommendation according to motor cable length and previous
multiplication factors.
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Software overvoltage limitation function
The over voltage software function (SUL) permits the limitation of the over voltage in
motor terminals to 2 times the DC bus voltage.
To do this, the minimum time between two PWM voltage pulses is adjustable as a
function of the cable length (from 6 to 10µS) by means of the optimization paramenter
“SOP”. The value of the “SOP” parameter corresponds to the attenuation time of the
cable used. It is defined to prevent the superimposition of voltage refections resulting
from long cable lengths.
The SUL function is useful by itself below certain wiring distances. For longer cable
lengths it is necessary to add additional output filters.
This function is based on the elimination of shorter pulses generated in the PWM output
of the drive. On the other hand, the elimination of these pulses leads to a little loss of
torque estimated about 3%, that leads in a lower dynamic performance.
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Software overvoltage limitation function
A PWM pulse too short with
respect to the time constant of
the cable can lead to the
superposition of 2 oscillations
and generate and overvoltage
> 2*V bus DC
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Software overvoltage limitation function
Function not activated
overvoltages greater than 2Vdc
+ 2Vdc
Time [s]
+ 2Vdc
SUL function activated
Time [s]
● The increase of « tmin » slightly degrades the performance but in a proportion that is
acceptable with a long cable length.
● The switching frequency is automatically limited to the factory setting (2.5kHz to 4kHz)
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Software overvoltage limitation function
The tables in the programmation manuals gives examples of correspondence between
“SOP” parameter and the length of cable between the drive and the motor.
Unshielded "GORSE" cable type H07 RN-F 4Gxx:
* These tables are not available for drives of power higher than 75kW.
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Software overvoltage limitation function
The tables in the programmation manuals gives examples of correspondence between
“SOP” parameter and the length of cable between the drive and the motor.
Shielded "BELDEN" cable Type 2950x:
* These tables are not available for drives of power higher than 75kW.
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Software overvoltage limitation function
Summary:
● Principal
● A PWM voltage pulse time that is very short in comparison to the period can generate an
overvoltage >2 times the DC bus voltage during a positive to negative transition.
● This function permits the limitation of the overvoltage to 2 times the DC bus voltage.
● To do this, the minimum time between two PWM voltage pulses is adjustable as a
function of the cable length (from 6 to 10µS).
● This function is activated by the parameter SUL
● Applications
● Protection of motors against overvoltages greater than 2 Vbus DC
● Cable lengths up to 150m
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Maximum cable length depending on motor choke selection
See catalog in order to verify the
maximum cable length depending on
output filter selection.
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Sinus Filter
Sinus filter is a low bandwidth filter with a cutoff frequency below the switching
frequency (4 to 8kHz only).
Sinus filter is the best solution with ATV71 to solve overvoltage at the motor terminal for
long motor cable until 600m or 1000m depending on the drive power rate. Sinus filter is
also the best way to reduce motor noise.
For high power rates sinus filter only allows U/F motor control law and low dynamic.
Vector control law in open loop is only posible until 75kW N4 or 45kW M3X voltage
supply.
See catalog in order to select the rigth reference.
In next page you will find a table with maximum cable length depending on sinus filter
reference.
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Sinus Filter
Maximum cable length depending on sinus filter reference:
For motors in parallel, the sum of all the cable lengths must be taken into
consideration. Due to capacitor between phases and ground at the output of the sinus
filters, the maximum length of each cable must be divided:
● by 2,5 for two motors
● by 4 for three motors
● by 6 for four motors
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Output side of ATV61/71
Motor choke vs. Sinus filter
● Motor choke …
● is much cheaper than a sinus filter
● has a smaller size, nearly no voltage drop, less losses
● Has a better peak voltage limitation against earth
● Allows all motor control laws (Sinus filter in HHP only allows U/f and low
dynamic)
● No drive derating necessary (Sinus filter operates at 4kHz!)
Altivar
61/71
M1
3
Motor choke
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Adequation of the motor
● Check is the selected motor is compatible with pre-selected drive and
options
1. Pe-selected configuration: L < Lmax with no motor filter
●Motor insulation must be compatible for the use with the variable speed
drive. Refer to the next slide.
●If not, it is required to add motor choke to protect the motor again dv/dt
and over voltages
Note: activation of the SUL function and adjustment of the parameter
SOP according to the type and length of cable suppress the over
voltages exceeding 2 times the bus voltage.
2. Pre-selected configuration: L > Lmax with motor choke and filter
●The motor is protected against dV/dT
●Motor protection against over-voltages can be considered by SUL
function activation.
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Adequation of the motor Motor
protection against dV/dT
● dV/dT protection : customer must be aware of the motor type intended
to be used in its application,
● We consider here the dV/dT on motor terminals.
● Depending on this type, IEC 60034-17 defines a table for admissible dV/dT
levels.
Overvoltage kV
● A – motors up to 500V used with a variable speed drive
● B – motors up to 600V used with a variable speed drive
● C – motors not specified for use with
variable speed drives (IEC60034-17)
Rise time µS
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Adequation of the motor Motor
protection against dV/dT
● Independently of motor cable length, the limitation of dV/dT to 500V/µs or
1kV/µs (depending on supply voltage) is done by using a motor choke:
● dV/dT limitation values with motor chokes:
< 500V/µs
@ 400V
< 750V/µs
@ 500V
< 1000V/µs
@ 690V
● The motor choke also permits to reduce peak voltage (*).
< 1000V @ 400V
< 1150V @ 460V
< 1800V @ 690V
* (These values apply in motor mode operation).
● The use of a motor choke is mandatory in case of retrofit of an installation with an old
motor.
● Supression of the dV/dT :
● The suppression of the dV/dT on motor terminals is done by using a sinus filter.
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Adequation of the motor Motor
protection against over-voltage
● A PWM voltage pulse time that is very short can generate an overvoltage >2 times the DC bus voltage during a positive to negative
transition.
● The variable speed drives integrates the SVL function, that permits the
limitation of the over-voltage to 2 times the DC bus voltage.
● In generative mode, the DC bus level will regulated at the DC bus braking level, that can be
adapted via UBR parameter:
●ATV71oooM3p: factory setting 395 V.
●ATV71oooN4: factory setting 785 V.
●ATV71oooS6X: factory setting 980 V.
●ATV71oooY: factory setting 1127 V or 1080 V according to rating.
● The activation of SVL function will limit the setting range of the
switching frequency of the variable speed drive.
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IEC 60034-25
● Find more information about
●
●
●
●
●
●
Motor cabling
Motor Isolation
Reduction of voltage stress
Bearing problems and causes
Motor filters
Drive principals
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