An IGBT failure is often the result, not the root cause.
When a VFD trips on overcurrent—or an IGBT is damaged—simply replacing the IGBT may not solve the problem.
Here are 5 common causes engineers should check:
1️⃣ Output Short Circuit
A phase-to-phase short circuit, motor winding fault, or damaged cable insulation can generate extremely high current.
The IGBT may be exposed to current far beyond its safe operating area.
🔧 Check: Motor insulation, output cables, terminals and phase-to-phase resistance.
2️⃣ Excessive Load or Locked Motor
A mechanically jammed motor, overloaded conveyor, blocked pump or compressor can cause the motor to demand excessive torque.
The VFD responds by increasing output current—and the power devices take the stress.
🔧 Check: Mechanical resistance and actual motor load before increasing VFD capacity.
3️⃣ Acceleration Time Too Short
A high-inertia load requires significant torque during acceleration.
If the acceleration time is too short, the VFD may reach its current limit or trigger an overcurrent fault.
🔧 Solution: Increase acceleration time or evaluate whether braking/drive capacity needs to be increased.
4️⃣ Excessive Switching Temperature
IGBT losses increase with switching frequency and output current.
Poor cooling, blocked air ducts, high ambient temperature or a failed cooling fan can cause the junction temperature to rise beyond its safe operating range.
🔧 Check: Heatsink temperature, cooling fan, ventilation and switching frequency.
5️⃣ Voltage Spikes & Motor Cable Reflections
Long motor cables can create reflected-wave voltage at the motor terminals.
High dv/dt and voltage spikes can stress the IGBT and motor insulation, especially in systems with long cables or fast switching devices.
🔧 Possible solutions: Output reactor, dv/dt filter or sine-wave filter, depending on the application.
🔍 The Important Point
When an IGBT fails, don't just replace the component and restart the VFD.
Check the entire system:
VFD → Motor Cable → Motor → Mechanical Load → Cooling System
The real cause may be outside the VFD itself.
An overcurrent fault is a warning.
An IGBT failure is often the consequence.
#VFD #IGBT #VariableFrequencyDrive #PowerElectronics #MotorControl #ElectricalEngineering #IndustrialAutomation #VFDTroubleshooting #Engineering
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