DC Bus Undervoltage

What does Uv1 mean?

The DC bus voltage fell below the undervoltage detection level (e.g., ~190V for 200V class, ~380V for 400V class) while the drive was running, or specific parameter conditions were met. Common causes include input power phase loss, loose wiring, unstable voltage supply, or worn main circuit capacitors.

• Input line voltage sag or loss on one or more phases (L1/L2/L3) to the drive.
• Inadequate main power supply capacity, causing voltage drop during motor acceleration or heavy load.
• Faulty pre-charge resistor or contactor preventing proper DC bus charging.
• Loose connections in the main power circuit to the drive or upstream circuit breakers.
• Excessive transient load causing a rapid DC bus voltage drop.

Click steps to track your progress.

1. 1

   1. Measure the incoming AC line voltage (L1-L2, L2-L3, L3-L1) at the drive input terminals using a true RMS multimeter to ensure it's within specified range.

2. 2

   2. Check for loose terminal connections on the main power input to the drive and upstream circuit breakers/contactors.

3. 3

   3. Monitor the DC bus voltage (P/N terminals) during operation using drive diagnostics (e.g., U1-07) or an external DC voltmeter to observe the drop.

4. 4

   4. Verify the integrity of the pre-charge circuit components (resistors, contactors, relays) if accessible and identifiable.

5. 5

   5. Ensure the main supply transformer or grid connection can handle the drive's peak current demand without significant voltage sag.

6. 6

   6. Adjust undervoltage ride-through parameters (e.g., L2-01) if nuisance tripping occurs during momentary sags that don't affect operation.