Brake set-up
shows the brake set-up in the VLT
®
Integrated Servo Drive ISD 510 System.
130BF780.10
AUX 1
Status
Hand
On
Reset
Auto
On
OK
Back
Can
cel
In
fo
Quick
Menu
Main
Menu
Alarm
Log
AUX 2
SAFE 1
SAFE 2
SAB
400-480 V AC
Real-Time Ethernet
UDC
2
ISD 510
3
. . .
. . .
1
4
1 I
brake
2 P
Line
3 P
ISD
4 Brake resistor R
brake
: Absorbs brake power P
brake
.
Illustration 2.15 Brake Set-up
Brake resistance
To prevent the SAB from cutting out for protection when
the servo drives are braking, select brake resistor values on
the basis of the peak braking power.
Rbrake
Ppeak brake
=
UDC
2
The SAB starts braking when the UDC voltage exceeds
778 V.
The brake resistor can range from 54.6–200 Ω. Brake
resistors within this range are detected by the configurable
brake check. The brake check is executed each time before
the SAB enters the state
Operation enabled
and when
mains is powered up. The brake check activates the brake
and checks if the DC-link voltage drops.
The minimum brake resistance is 54.6 Ω. When higher
brake resistor resistance is selected, the maximum braking
torque cannot be reached, and there is a risk that the SAB
will cut out due to DC-link overvoltage protection.
Calculation of brake power
When calculating the brake power, ensure that the brake
resistor is scaled for the average power as well as for the
peak power.
•
The peak brake power depends on the number of
servo drives that are in acceleration mode and
deceleration mode. The torque used to accelerate
and decelerate is also important.
•
The average power is determined by the process
period time, for example the length of the
braking time in relation to the process period
time.
Calculation of brake resistor peak power
The brake active voltage for the SAB is 778 V. When using
the minimal brake resistance of 54.6 Ω, a current of
14.25 A will flow at 778 V.
The brake resistor peak power is then calculated as follows:
Ppeak brake
UDC2
Rbrake min
778 V x 778 V
54.6 Ω
=
=
=
11086 W
If the application does not require braking with the
maximum current, a higher brake resistance can be
selected. A higher brake resistance results in a lower brake
peak power.
When the servo drives are accelerating, P
ISD n
is positive.
When the servo drives are decelerating, P
ISD n
is negative.
If the sum of all P
ISD
connected to the SAB results in a
negative value, the energy must be absorbed in the brake
resistor.
If the sum of all P
ISD n
is positive, energy from the mains is
converted into rotation energy and the brake resistor does
not need to absorb energy.
To calculate the peak brake power, select the moment
where the most servo drives are decelerating and the
fewest servo drives are accelerating.
The peak power of a decelerating servo drive can be
calculated as:
Ppeak ISD
=
ηISD x ωStart x j x
Δt
Δω
Ppeak ISD
=
ηISD x nStart x
x j x
60
2 x π
Δt
Δn
( )
j: Shaft inertia
n
ISD
: Efficiency of the servo drive (typically 0.88)
System Overview
Design Guide
MG36C102
Danfoss A/S © 08/2017 All rights reserved.
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