7.12 Dynamic Braking
Dynamic braking is a method to slow down a servo system by dissipating the mechanical
energy driven by the motor back EMF. The AKD-N drives have a built in advanced dynamic
braking mode which operates fully in hardware. When activated, the drive shorts the motor
terminals in phase with the back EMF (q axis) but continues to operate the non-force pro-
ducing current loop (d-axis) with 0 current. This forces all of the dynamic braking current to be
stopping current and insures the fastest stopping/amp of motor terminal current.
When current is not being limited, the mechanical energy is being dissipated in the motor
resistance.
When current is being limited, energy is returned to the AKD-C bus capacitors.
The drive also limits the maximum dynamic braking motor terminal current via the
DRV.DBILIMIT
parameter to insure that the drive, motor, and customer load do not see
excessive currents/forces.
Whether and how the AKD uses dynamic braking depends on (
DRV.DISMODE
).
7.13 Regen circuit
When the amount of returned energy from the AKD-N builds the bus capacitor voltage up
enough, the AKD-C activates the regen circuit to start dumping the returned energy in the
regen resistor (also called regenerative or brake resistor). The AKD-C has an internal regen
resistor, an additional external one can be connected to X14.
External regen resistors are described in the regional
Accessories Manual
.
7.13.1 Functional description
When the amount of returned energy builds the bus capacitor voltage up enough, the AKD-C
activates the brake chopper to start dumping the returned energy in the regen resistor at the
AKD-C (internally or connected to terminal X14). 90% of the combined power of all the
coupled drives is always available for peak and continuous power.
The drive that has the lowest switch-off threshold (resulting from tolerances) reports an over-
voltage fault if the DC bus threshold is exceeded. The drive power stage is disabled and the
load coasts to a stop with the fault message “F501 Bus Over voltage" (
# 87). The AKD-C
fault relay contact (terminals X15/5-6) is opened due to this fault.
7.13.2 Technical data
Observe the regeneration time (some minutes) after full load with peak regen power.
Rated data
Units
400 V
480 V
Switch-on threshold of regen circuit (nominal)
V
760
760
Overvoltage limit
V
840
840
Maximum regen duty cycle
%
15*
15*
Internal regen resistor
Ohm
33
33
Continuous power, internal resistor
W
100
100
Peak regen power, internal resistor (0.5s)
kW
17.5
17.5
External regen resistor
Ohm
33
33
Maximum continuous regen power, external resistor
kW
1.5
1.5
Peak regen power, external (1s)
kW
17.5
17.5
Absorption energy in capacitors (+/- 20%)
Ws
21
7
DC Bus Capacitance (nominal)
µF
585
585
* depends on connected regen resistor power
AKD-C Installation | 7 Technical description and data
Kollmorgen | kdn.kollmorgen.com | February 2018
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