How to Troubleshoot IGBT Faults in a Variable Frequency Drive

IGBT (Insulated Gate Bipolar Transistor) modules are among the most critical — and most failure-prone — components in a Wolong VFD's power section. When a drive trips on an IGBT-related fault, a systematic approach helps identify the problem quickly and prevents repeat failures after replacement. The general troubleshooting sequence follows a "static first, then dynamic" approach: check the module with a multimeter while powered off, then analyze the fault behavior during operation.

Step 1: Static Testing (Power Off)

This is the safest and most fundamental diagnostic step. Using a multimeter's diode test function, measure the IGBT module's freewheeling diode with the drive completely powered off.

How to test:

• Set the multimeter to diode test mode

• Measure between the Collector (C) and Emitter (E) terminals

• Measure between the Gate (G) and Emitter (E) terminals

Normal readings:

• C-E should show diode characteristics (conducts in one direction only)

• G-E should show high resistance (essentially no conduction)

Fault indicators:

• C-E shorted in both directions, or open in both directions

• G-E showing very low resistance or a short circuit

Any of these results indicate the IGBT module has failed.

Step 2: Dynamic Fault Analysis (Powered Operation)

If IGBT faults occur repeatedly during operation, the fault code and operating symptoms need to be analyzed together.

IGBT open-circuit faults are the most common failure type. Symptoms typically include phase loss under load, current imbalance, and motor vibration or loss of torque. While advanced diagnostic methods (such as switching function models or average current Park vector analysis) can pinpoint the exact failed phase and device, in routine field maintenance, cross-referencing the fault code with three-phase current measurements is usually sufficient to locate the problem.

Overvoltage breakdown faults are a critical consideration. In many real-world cases, IGBT failure is not caused by component aging but by voltage spikes at turn-off. A well-documented example is a metro transit system where a voltage spike during chopper IGBT turn-off caused a cascading failure of the IGBT, driver board, and interface board. This means that when an IGBT is found burned out, it should not simply be replaced — the DC bus voltage stability and snubber (absorption) circuit must also be checked. Otherwise, the replacement IGBT is likely to fail again.

Safety Precautions

High voltage risk: The DC bus capacitors in a VFD's main circuit store significant electrical energy even after power is disconnected. Wait at least 5–10 minutes after power-off, until the charge indicator light goes out and a multimeter confirms the bus voltage has dropped to a safe level (below 36V), before opening the unit or taking measurements.

Related component damage: When an IGBT is destroyed by a voltage breakdown, the resulting high voltage often damages associated driver circuit components as well — optocouplers, driver ICs, or isolated power supplies. After replacing an IGBT, the driver circuit must be inspected or replaced together with it. Skipping this step risks immediate re-failure on power-up.

Troubleshooting Summary

Power off → Static resistance test → Confirm failure → 
Identify root cause (driver circuit / voltage spike) → 
Replace with same-model component → Power-on test