Flux Braking - Control Techniques Commander SE Advanced User's Manual

12.23

Flux Braking

The following set-up can be used to dissipate more energy in a motor while decelerating and therefore it has the possibility of
eliminating the need for a braking resistor. This may be especially useful on Commander SE size 1 which does not have the
capability of dynamic braking.
Set-up
This set-up can be used on a standard 50Hz motor.
1.21 = 40.5
1.22 = 20.0
2.04 = 0
12.03 = 5.01
12.04 = 70
12.06 = 1
12.07 = 14.06 Threshold destination to PID feedback invert
14.02 = 1.21
14.04 = 1.22
14.08 = 1
14.10 = 0
14.11 = 1
14.13 = 1.0
14.14 = 0.0
14.16 = 5.06
Perform a Save routine: xx.00 = 1000 and press red Stop / Reset button on the drive
Operation
When the drive is in the 'rd' condition, the motor rated frequency (parameter 39) will be set to 50.0 which is the standard
setting for a 50Hz motor. When the drive is given a run command and the motor frequency is increased, the correct V/f profile
will be followed until the motor frequency reaches the programmable threshold % value set in parameter 12.04 (70% in this
example). At this point, the motor rated frequency will be decreased to 40Hz (set by parameter 1.21). The rate at which the
motor rated frequency decreases can be adjusted by changing the value in preset speed 2 and/or the PID integral gain value.
The V/f characteristic will be slightly incorrect for the motor as the frequency is increased from 40 to 50Hz but this should not
cause any problems with performance, etc.
When the drive is given a stop command and the motor frequency is reduced, the motor volts will remain high until the
programmable threshold level is reached and then the motor volts will reduce back to the standard V/f characteristic.
The motor volts remaining high for the first part of the deceleration ramp overfluxes the motor. This has the effect of
increasing the losses within the motor and therefore reduces the amount of energy being transferred back to the drive.
Increasing the losses in the motor will cause the motor temperature to increase slightly.
In experiments with a set inertia, implementing this set-up has allowed the deceleration ramp to be decreased by
approximately 30% without OV trips occurring.
The following plots show the standard V/f curve and the flux braking V/f curve during the acceleration and deceleration
ramps.
V/f Curve during acceleration
300
250
200
150
100
50
0
Commander SE Advanced User Guide
Issue Number: 4
Preset speed 1 to 40.5Hz (customer adjustable for different speed motors - 60Hz etc.)
Preset speed 2 to 20.0Hz (customer adjustable in conjunction with PID integral gain to set time for the
motor rated frequency to change from 40Hz to 50Hz and vice versa)
Fast ramp stopping mode selected
Threshold source from motor frequency
Threshold level set at 70% (customer adjustable, sets motor frequency at which V/f curve changes.
Setting lower than 70% may cause OV or OI.AC tripping of the drive)
Threshold output inverted
PID main reference source from preset speed 1
PID feedback source from preset speed 2
PID enabled
PID P gain set to 0
PID I gain to 1.0
PID high limit to 1.0
PID low limit to 0.0
PID destination to motor rated frequency
0 10 20 30
Ouput Frequency
Motor Volts - Flux
braking
Motor Volts -
Standard Set-Up
40 50
185