Electrical Motor Braking

Drive dynamic braking

Drive Dynamic braking is a method to slow down a servo system by dissipating the mechanical energy driven by the motor back EMF.

Drive dynamic braking is not functional safe. Safe dynamic braking (SDB) requires an external SDB-Contactor (see "SDB (Safe Dynamic Brake)").

The drive has a built in advanced drive dynamic braking mode which operates fully in hardware. When activated, the drive powers the motor terminals with voltages to maximize the stopping force per amount of motor current. This advanced method forces all of the dynamic braking current to be stopping current and insures the fastest stopping per ampere of motor terminal current.

  • When current is not being limited, the mechanical energy is being dissipated in the motor winding resistance.
  • When current is being limited, energy is returned to the drive bus capacitors.
  • The drive also limits the maximum dynamic braking motor terminal current by using the AXIS#.DBILIMIT parameter to insure that the drive, motor, and customer load do not see excessive currents/forces.

Whether and how the drive uses dynamic drive braking depends on AXIS#.DISMODE.

Regenerative braking

When the amount of returned energy from the motor builds the bus capacitor voltage up enough the drive activates the regenerative braking circuit to start dumping the returned energy in the regen resistor (also called regenerative resistor or brake resistor). The AKD2G drives offer internal resistor plus the ability to connect an external resistor depending on the application requirements.

For more information on external regen resistors, see the Accessories Manual.

Functional description

1. Individual drives, not coupled through the DC bus link circuit (+DC, -DC)

When the energy fed back from the motor has an average or peak power that exceeds the preset level for the brake power rating, the drive generates the warning "W2010 Regen Energy Critical”. If the power exceeds the set fault level, the regenerative circuit will switch off and the drive will disable.

2. Several drives coupled through the DC bus link (+DC, -DC)

Only with group installation

Using the built-in regenerative circuit, several drives of the same series can be operated from a common DC-bus link (see "DC Bus link connector X3/X3B"), without any additional measures. 90% of the combined power of all the coupled drives is always available for peak and continuous power. If the power of the drive with the lowest switch-off threshold (resulting from tolerances) exceeds the set fault level, the regenerative circuit will switch off on that drive.

Switch-off on over voltage: With the regenerative circuit switched off, the returned energy is not dissipated and therefore the DC-bus link level increases. The drive reports an over-voltage fault if the DC-bus voltage threshold is exceeded. When this happens, the drive power stage is immediately disabled and the load coasts to a stop with the fault message “F2006 Bus Over voltage".
The ready to operate contact (terminals X21/B5-B6) is opened (see "Digital-Out 9, Relay contacts").

Observe the regeneration time (some minutes) after full load with peak brake power.

Technical data – 240V servo drives

Technical data for the regenerative circuit depends on the drive type and the mains voltage. Supply voltages, capacitance, and switch-on voltages are all nominal values.

Brake circuit

 

AC Supply

Model

Rated data

Units

120V / 240V

6Vxxy
all types

Regen start voltage at rated supply voltage

V

380

Overvoltage limit

V

420

Maximum regenerative duty cycle

%

35*

Internal regen resistor

Ω

15

Continuous power, internal resistor

W

100

Peak brake power, internal resistor (0.5s)

kW

3 / 9

External regen resistor (recommended 33 Ω)

Ω

≥10

Continuous brake power, external resistor

kW

3

Peak brake power, external (1s)

kW

5 / 14

6V03S, 6V06S

Absorption energy in capacitors (±20%)

Ws

6 / 23

DC Bus Capacitance

µF

1640

6V12S, 6V03D, 6V06D

Absorption energy in capacitors (± 20%)

Ws

9 / 35

DC Bus Capacitance

µF

2460

* depends on connected regen resistor power.

Brake circuit

Brake circuit

 

AC Supply

Model

Rated data

Units

240V

400V/480V

7V03S ,7V06S, 7V12S, 7V03D, 7V06D

Regen start voltage at rated supply voltage

V

380

633 / 760

Overvoltage limit

V

420

840

Maximum regenerative duty cycle

%

35*

Internal regen resistor

Ω

33

Continuous power, internal resistor

W

100

Peak brake power, internal resistor (0.5s)

kW

4

17

External regen resistor (recommended 33 Ω)

Ω

≥25

Continuous brake power, external resistor

kW

2

6

Peak brake power, external (1s)

kW

6

24

7V03S, 7V06S

Absorption energy in capacitors (±20%)

Ws

3

30 / 18

DC Bus Capacitance

µF

235

7V12S, 7V03D, 7V06D

Absorption energy in capacitors (±20%)

Ws

6

50 / 35

DC Bus Capacitance

µF

470

 

AC Supply

Model

Rated data

Units

240V

400V/480V

7V24S

 

Regen start voltage at rated supply voltage

V

380

633 / 760

Overvoltage limit

V

420

840

Maximum regenerative duty cycle

%

35*

Internal regen resistor

Ω

15

Continuous power, internal resistor

W

140

Peak brake power, internal resistor (0.5s)

kW

9

38

External regen resistor (recommended 15 Ω)

Ω

≥10

Continuous brake power, external resistor

kW

3

10

Peak brake power, external (1s)

kW

14

55

Absorption energy in capacitors (±20%)

Ws

15

125 / 80

DC Bus Capacitance

µF

1200

* depends on connected regen resistor power.