VFD Overvoltage on Deceleration? The Motor May Be Returning Energy
A DC-bus overvoltage trip that occurs while slowing down can be related to energy returning from the moving load. A shorter stopping ramp is not always achievable with the installed drive and braking arrangement. Check the event timing, supply conditions, and approved stopping design together.
Altivar behavior is a reference example; braking design is application-specific.
What is happening?
During deceleration, some applications regenerate energy into the drive's DC link. The installed system must handle that energy through its supported arrangement. Schneider documents deceleration-ramp adaptation on applicable Altivar drives, which may extend deceleration to limit bus overvoltage. That feature does not establish an acceptable machine stopping time by itself.
Check these five things
-
Record the exact trip code and whether it occurs during acceleration, steady operation, or deceleration.
-
Compare the requested ramp with the commissioned stopping profile and current load inertia.
-
Review drive diagnostics and supply conditions using the manufacturer's approved measurement method and qualified personnel.
-
Check the specified braking or regenerative equipment and its configuration against the design. Stored energy requires the prescribed isolation and discharge procedure.
-
Have the responsible engineer assess any ramp or braking change against process requirements and safety-related stopping functions.
Worked example
A loaded rotating system trips only during a newly shortened stop ramp. That timing supports investigating regenerative energy and the stopping design. Simply enabling automatic ramp extension could also make the machine take longer to stop, so acceptance criteria must include actual stopping behavior.
Quick diagnostic reference
| Question | Evidence |
|---|---|
| When does voltage rise? | Fault trace and speed profile |
| What changed? | Ramp, load, braking configuration |
| Is the result acceptable? | Reviewed stopping-time requirements |
The mistake to avoid
Do not prescribe a generic braking resistor value. Compatibility, duty, energy, thermal protection, and drive support must be engineered for the application.
How to verify the fix
Confirm the complete approved stop profile without overvoltage faults and verify every applicable stopping-time requirement.
Field-work boundary: These are educational diagnostic guides. Use the exact equipment manuals and approved site procedures. Electrical testing and machinery changes belong to qualified, authorized personnel; control hazardous energy and validate affected functions before release.
Technical reference
Schneider Electric: deceleration ramp adaptation on Altivar drives. The examples and diagnostic tables above are original teaching material; they do not replace the product manual.