7.3
Common Functions
- 19
J
Megnetic Flux Compensation: b2--08 (for SPEC: F)
When the DC injection braking time at start (initial excitation) function is used to start the motor magnetic
flux before operating machinery requiring high starting torque, particularly with large--capacity motors,
the startup of the magnetic flux may take some time due to the effect of the electrical time constants of the
motor.
Use the magnetic flux compensation function to supply a strong magnetic flux current when starting the
DC injection braking time at start (initial excitation). This will increase the speed and stability of the mo-
tor’s internal megnetic flux startup.
User
Change
during
Setting
Factory
Valid Acces Levels
User
Constant
Number
Name
during
Opera-
tion
Setting
Range
Unit
Factory
Setting
Open Loop
Vector
Flux Vector
b2--03
DC injection braking
time at start
0.00 to
10.00
0.01
s
0.00
B
B
b2--08
Magnetic flux com-
pensation volume
0 to 500*
1%
0
A
A
When b2--08 is 100%, it indicates the motor no--load current (motor magnetic flux current).
During base block
Run command
Control mode
Motor’s magnet-
ic flux current
Output
frequency
b2--08
b2--03
During DC injection braking time at start (initial excitation)
During speed control
Motor’s
magnetic flux
current during
control
Limited to smaller of 80% of the inverter’s rated
current of the motor’s rated current.
b2--08=100%
Fig
7.9
Time Chart for Magnetic Flux Compensation
D
If b2--08 is set at 100% or greater, a stronger current can be supplied when starting DC injection braking
time at start (initial exciation), and the motor’s internal magnetic fulx startup can be speeded up. The
startup time can be reduced by approximately half when the b2--08 is set to 200%.
D
The magnetic flux startup is slower if b2--08 is less than 100%. (Do not normally set b2--08 to less than
100%. However, the operation will be the same as b2--08 = 100% when b2--08 = 0%, and the startup
will be at the set DC injection braking current (b2--02).
D
If the magnetic flux compensation volume (b2--08) is set to a large value, there may be greater noise
generated from the motor during DC injection braking time at start.
D
The electrical time constant when the motor’s magnetic flux is started (secondary circuit time constant)
can be calculated using the motor constant E2 setting and the following formula:
Secondary circuit time constant T2 = [E2--01
2
--E2--03
2
)
1/2
/(2 x E2--02 x E2--03)] (sec)
D
Do not use this function when slow commencement of braking due to DC injection braking time at
start (initial exciation) is becoming a problem. Use the separate DC braking command (setting: 60)
for multi--function contact input, and start the motor magnetic flux beforehand while stopping the mo-
tor.
7