VFD overvoltage during deceleration
When a motor is slowed faster than the load would coast, it acts as a generator and pushes energy back into the drive’s DC bus. If the drive cannot absorb or dissipate that energy, the DC bus voltage rises until it trips on overvoltage.
Diagnose this with AI
Try Free Drive Diagnostic Upload a photo of the alarm screen, the fault history or a data export. InduQT compares the evidence and suggests the next useful checks.
Where it shows up
- A DC bus (DC link) overvoltage fault during stops or speed reductions
- Trips more often with heavy, high-inertia loads
Likely causes and how to tell them apart
1Deceleration time too short
- Points to it
- Trips only on fast stops or large speed changes.
- Check
- Lengthen the deceleration time and compare the DC bus voltage at the end of the ramp.
2Overvoltage control disabled
- Points to it
- The drive’s automatic overvoltage controller is switched off in parameters.
- Check
- Check whether the overvoltage controller is enabled, unless a braking chopper is fitted and the manual says to disable it.
3Braking resistor or chopper not working
- Points to it
- Resistor fitted but stays cold; chopper fault or disabled in parameters.
- Check
- Verify the resistor value and wiring and that braking is enabled, following the drive manual.
4High supply voltage
- Points to it
- Trips even on gentle stops; supply measured near the top of tolerance.
- Check
- Measure the incoming line voltage and compare with the drive’s rating.
Diagnostic sequence
- Confirm the momentCheck the fault log: was the drive decelerating when it tripped?
- Look at the loadHigh inertia or overhauling loads regenerate the most energy.
- Check settingsDeceleration time, overvoltage control and braking settings.
- Decide on brakingIf the process needs fast stops, size a braking resistor or regenerative unit per the manufacturer.
Evidence to collect
- Fault log with DC bus voltage at the trip
- Deceleration time and braking settings
- Whether a braking resistor is fitted
- Incoming supply voltage
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