DC Bus Undervoltage

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This fault occurs when the DC bus voltage drops below a critical detection level, which is approximately 190V for 200V class drives and 380V for 400V class drives (or 350V when E1-01 < 400V). Common causes include phase loss in the input power, loose wiring, unstable input voltage, or issues with main circuit capacitors or the soft-charge bypass relay. Persistent undervoltage can lead to unreliable drive operation, component damage, or complete shutdown of the system.

• Transient voltage sag or complete interruption on the incoming AC mains supply (L1, L2, L3).
• Loose or corroded electrical connections at the drive's input terminals (R/L1, S/L2, T/L3) or upstream.
• Failure of the drive's internal input rectifier bridge or DC bus capacitors.
• Overloaded power distribution network causing a sustained drop in supply voltage.
• Incorrect E1-01 (Input Voltage Selection) setting for the connected mains supply voltage.

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1. 1

   Measure the incoming AC line voltage (L1-L2, L2-L3, L3-L1) at the drive's input terminals with a multimeter.

2. 2

   Inspect all power wiring terminations, including circuit breakers and contactors, for tightness and absence of corrosion.

3. 3

   Monitor the DC bus voltage (parameter U1-06) during motor operation and under varying loads.

4. 4

   Verify E1-01 (Input Voltage Selection) is correctly set to match the nominal line voltage (e.g., 400V).

5. 5

   Check upstream power quality and grid stability to identify potential external supply issues.