Scope of this technical record
Generic three-phase VFD power-stage orientation: input protection, rectifier, precharge, DC-link capacitor bank, brake chopper, gate-driver interface, IGBT/IPM bridge and motor output.
This is a functional reference for repair planning only. Do not probe, discharge, megger or energize a drive outside qualified procedures and the specific OEM manual.
The power stage is a chain, not a single module
A VFD power stage is usually discussed as the input, DC bus and output bridge. For repair, the more useful view is a chain of failure boundaries: line supply and fusing, rectification, precharge, DC-link storage, braking energy handling, gate-drive command, semiconductor switching, current feedback and the motor-cable path.
A fault near one end of the chain can destroy another part. A motor-cable ground fault can take out a good module; a weak gate supply can damage a new IGBT; a failed brake path can overstress the DC link. That is why the page links to overcurrent, ground fault, overvoltage and repeat-module workflows rather than treating the power stage as one replacement item.
Service split by evidence
The same static diode or resistance reading can be misleading across brands and module topologies. The service decision should combine static power-stage checks, event timing, bus condition, external output path and previous repair history.
Power-stage evidence route
| Evidence | Likely area | Service decision |
|---|---|---|
| Input fuse opens before display | Rectifier / precharge / DC link | Inspect input and charge path before output module |
| Trip at first PWM output | Motor cable / output bridge / driver | Separate external path from inverter hardware |
| Module failed after replacement | Driver / current feedback / external load | Stop until gate and sensing paths are proven |
| Overvoltage only on stop | Brake / machine energy | Avoid replacing power board before braking route is checked |
| Ground fault only when run | Motor insulation / output leakage | Do not megger through the drive |
Field record checklist
- Drive frame and voltage class
- Static module condition
- First trip timing
- Bus capacitor and precharge evidence
- Motor/cable insulation boundary
- Gate-driver and current-feedback photos
Technical basis and reference documents
This is an independent editorial technical reference. Original manufacturer documentation remains controlling for installation, repair and commissioning decisions.
Related circuit page for input energy routing.
Related circuit page for module survival checks.
Related technical records
The drive trips on overcurrent immediately at run command, during initial acceleration or before the motor reaches speed.
The drive runs normally but trips on overvoltage when stopping, ramping down, lowering a load or decelerating a high-inertia machine.
The drive powers up but trips on ground fault, earth fault or leakage indication during enable, acceleration or when output voltage is applied.
A replacement output module, IPM or IGBT pack fails during the first power-up, first run test or shortly after returning the drive to service.
Routes incoming three-phase supply through protection, rectification, precharge and DC-link storage before the inverter stage is allowed to run.
Connects PWM command, isolated driver supply, gate components, short-circuit protection and the output bridge to overcurrent and repeat-module-failure symptoms.
Routes excess DC-link energy into braking hardware or controlled overvoltage management during deceleration and overhauling-load events.
Drive reports undervoltage/precharge fault, blows input fuses or shows no-display symptoms with uncertain DC-link charging.
Overcurrent trip appears immediately at run command, during acceleration or before stable speed is reached.
Replacement IGBT, IPM or output module fails again during power-up, enable or early load testing.
Turn this record into a qualified service request
A repair decision is much more reliable when the request includes the exact identity of the drive, the first fault evidence and the machine condition when the symptom appeared.
- Complete drive type code / MLFB or nameplate model
- Fault code, fault value and first event before reset
- When the event appears: power-up, enable, ramp, run, decel or stop
- Motor/cable connected or isolated during the symptom
- Visible board, option-card, module and connector identifiers
- Previous repair history, replacement parts and repeat-failure pattern