Dynamic and static measurement methods for IGBT drive circuit of frequency converter

Preparation Work!

1. Please ensure that the frequency converter is completely powered off and wait for 510 minutes for the internal capacitor to discharge completely (many frequency converters have a discharge indicator light, wait for it to turn off).
2. Prepare a digital multimeter.
3. Remove all external wiring (power lines, motor lines, etc.) of the frequency converter to ensure that only the body is measured.

And here, we use a three-step to determine if the IGBT circuit is functioning properly

FIRST: Measure the input side (R/S/T) ——- determine the quality of the rectifier bridge

Multimeter gear: diode gear (you can use the buzzer gear, but the resistance/voltage drop reading should prevail).

Measurement method:

1. Fix the black probe (COM) on the “+” terminal of the DC bus.
2. Use a red probe to measure the R, S, and T input terminals in sequence.
3. Normal situation: The multimeter should display a forward voltage drop value of approximately 0.3V~0.6V across the diode, and the readings from the three measurements should be roughly equal.
4. Fix the red probe on the “” terminal of the DC bus.
5. Use a black probe to measure the R, S, and T input terminals in sequence.
6. Normal situation: A diode forward voltage drop value of approximately 0.3V~0.6V should also be displayed, and the three readings should be roughly equal.

Judgment criteria:

Normal: Both forward and reverse measurements conform to the above rules, indicating that the diodes of the rectifier bridge (usually a three-phase full bridge rectifier) are basically normal.

Fault:

– Any measurement with a reading of 0 (or a long beep from the buzzer) indicates a breakdown or short circuit.

– Any measurement reading of OL (overflow or infinity) indicates an open circuit damage.

– The significant difference in readings from the three measurements indicates an imbalance in the performance of the rectifier bridge and a potential fault.

SECOND: Measure the output side (U/V/W) —– determine the quality of the inverter IGBT

Multimeter gear: diode gear.

Measurement method:

1. Fix the black probe (COM) on the “+” terminal of the DC bus.
2. Use a red probe to measure the three output terminals U, V, and W in sequence.
3. Normal situation: The multimeter should display OL (infinity) or a very high resistance value. Because at this point, it is equivalent to a reverse circuit through the anti parallel diode of IGBT, which is non-conductive.
4. Fix the red probe on the “” terminal of the DC bus.
5. Use a black probe to measure the three output terminals U, V, and W in sequence.
6. Normal situation: The multimeter should display a diode forward voltage drop value of approximately 0.3V to 0.6V, and the three readings should be roughly equal. This measures the forward voltage drop of the anti parallel diode inside the IGBT.

Judgment criteria:

Normal: There is a reasonable voltage drop in the forward direction (black pen connected, measuring UVW), and infinity in the reverse direction (red pen connected+, measuring UVW).

Fault:

In second-5, if any measurement reading is 0, it indicates that the IGBT or anti parallel diode of that phase has broken down and short circuited.

In second-5, if any measurement reading is OL, it indicates that the IGBT or anti parallel diode of that phase is open circuit damaged.

In third-3, a very small resistance or voltage drop (not OL) is measured, indicating that the IGBT or diode in that phase is short circuited due to breakdown.

THRID: Measuring DC bus (+/) ———– determining overall insulation and capacitance

Multimeter gear: Resistance gear (high resistance gear).

Measurement method:

1. Connect the probes to the “+” and “” on the DC bus respectively.

Judgment criteria:

Normal: At the beginning, there is a small resistance value (capacitor charging), and then the resistance value can steadily rise to a large value (several hundred k Ω or even OL), because you are charging the bus capacitor.

Fault:

A reading of 0 Ω or a very small fixed value indicates a serious short circuit between the busbars, which may be a blown IGBT, damaged capacitor, or rectifier bridge.

The resistance value always stays at a low value below tens of k Ω, indicating insulation degradation or component leakage inside.