Regenerative resistor
Servo drive with motor can act two ways: energy supply and energy generator. The generator behavior occurs during decelerations and this causes current flow from motor to drive power supply capacitors. If that generated energy is not absorbed anywhere, the voltage of capacitors will rise above overvoltage threshold and trigger an software clearable overvoltage fault.
 | In most installations braking resistor is not needed at all. Resistor is needed in cases where fast moving motor with high inertial load is stopped rapidly causing conversion of the kinetic energy into electric current which needs to be dissipated by a resistor. Experimenting without resistor is safe as drive's overvoltage protection will prevent any damage occurring. If drive faults to overvoltage fault during deceleration, then try adjusting Over voltage fault thresholdFOV to higher value or add a braking resistor. |
Overvoltage faults
Scenarios where returned energy is causing the rise of HV DC bus voltage:
- Deceleration of motor speed when there is significant amount of energy stored in mechanical motion (rotating inertia or moving mass). This typically occurs with spindles and linear axes.
- Sudden reversal of torque setpoint. This can generate voltage spike even when motor is standing still. This typically occurs in high bandwidth torque control applications (such as Force feedback system (FFB)). These spikes are very short and an added capacitor to HV DC bus and/or low resistance regenerative resistor can provide a solution.
Voltage generation during deceleration of motor (motor current is negative, current is pumped to HV DC bus causing a 40 VDC rise).
Voltage generation during deceleration of motor (motor current is negative, current is pumped to HV DC bus). However, in this case drive is equipped with regenerative resistor and tightly set Over voltage fault thresholdFOV parameter which prevents the significant voltage rise (only 5 VDC rise).
Example of accelerating motor (motor current is positive, power is drawn from HV DC bus which is causing a temporary voltage drop). Rectified 50 Hz mains AC ripple is easily seen in the voltage graph.
See also
- Overvoltage and undervoltage faults - practical guide for sizing regenerative resistor
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