Brake energy management
When braking electrical motors, the kinetic energy of the drive train is fed back regeneratively to the DC bus. This energy causes a DC-bus voltage boost. If the energy fed back is too high, the inverter reports an error.
Several different strategies can serve to avoid DC-bus overvoltage:
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Use of a brake resistor
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Stopping the deceleration ramp function generator when the active voltage threshold for the brake operation is exceeded
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Use of the "Inverter motor brake" function
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Combination of the above named options
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DC-bus connection
Details
The voltage threshold for braking operation results on the basis of the rated mains voltage set:
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Rated mains voltage
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Voltage thresholds for braking operation
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Braking operation on
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Braking operation off
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230 V
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DC 390 V
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DC 380 V
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400 V
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DC 725 V
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DC 710 V
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480 V
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DC 780 V
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DC 765 V
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The voltage threshold for braking operation can be reduced by 0 ... 100 V. The reduction required must be set in 0x2541:003 (P706.03). However, the reduction must be made to such an extent that the reduced voltage threshold is still above the normal stationary DC-bus voltage.The active voltage threshold for the braking operation is displayed in 0x2541:002 (P706.02).
If the DC-bus voltage exceeds the voltage threshold for braking operation, the braking method selected in 0x2541:001 (P706.01) is applied.
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Optimum following of the actual frequency value to the frequency setpoint (e. g. quick stop of the motor) can always be achieved by the use of a brake resistor.
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Stopping the deceleration ramp function generator enables smoother deceleration with lower torque oscillation.
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The "Inverter motor brake" function allows for quick braking without using a brake resistor. For process-related reasons, torque oscillations may occur.
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①
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Voltage threshold for braking operation
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0
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②
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Reduced threshold0x2541:003 (P706.03)
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1
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③
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Active threshold0x2541:002 (P706.02)
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2
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④
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Additional frequency0x2541:004 (P706.04)
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Parameter
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Address
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Name / setting range / [default setting]
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Information
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0x2541:001
(P706.01)
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Brake energy management: Operating mode
(Brake management: Operating mode)
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Selection of the braking method.
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The braking method(s) selected is/are activated if the DC-bus voltage exceeds the voltage threshold for the braking operation shown in 0x2541:002 (P706.02).
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0
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Brake resistor
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The integrated brake chopper (brake transistor) is used.
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1
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Ramp function generator stop (RFGS)
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The deceleration ramp function generator is stopped.
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2
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Brake resistor + RFGS
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The brake resistor is supplied with current and the deceleration ramp function generator is stopped.
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3
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Inverter motor brake (IMB) + RFGS
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Braking with the "Inverter motor brake" braking method in connection with "Deceleration ramp function generator stop" is executed.
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4
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Brake resistor + IMB + RFGS
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Braking is performed by combining all three braking procedures.
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0x2541:002
(P706.02)
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Brake energy management: Active threshold
(Brake management: Active threshold)
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Read only: x V
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Display of the active voltage threshold for the braking operation.
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The voltage threshold shown depends on the mains voltage selected in 0x2540:001 (P208.01) and the voltage value set in 0x2541:003 (P706.03).
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The voltage threshold must be higher than the stationary DC voltage in the DC bus.
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0x2541:003
(P706.03)
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Brake energy management: Reduced threshold
(Brake management: Red. threshold)
0 ... [0] ... 100 V
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The voltage threshold for the braking operation is reduced by the voltage value set here.
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0x2541:005
(P706.05)
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Brake energy management: Deceleration override time
(Brake management: Del.overr.time)
0.0 ... [2.0] ... 60.0 s
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Maximum permissible time for the deceleration override by means of the braking method selected in 0x2541:001 (P706.01).
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If the DC-bus voltage does not fall below the voltage threshold for braking operation shown in 0x2541:002 (P706.02) within this time, the motor is decelerated further.
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The time is only reset if the voltage threshold shown in 0x2541:002 (P706.02) is not reached.
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Use of a brake resistor