Cause : DC link voltage undervoltage comes when the power unit has detected an undervoltage condition in the DC link. When encountering a DC link voltage undervoltage fault with a Siemens SINAMICS G120 drive, it indicates that the voltage level in the DC link has dropped below the acceptable threshold. 

- line supply failure
- line supply voltage below the permissible value.
- line phase interrupted.

Note: The monitoring threshold for the DC link undervoltage is the minimum of the following values- for a calculation, refer to p0210

Remedy:

- check the line supply voltage
- check the line supply phases.
See also: p0210 (Drive unit line supply voltage)

Here's how you can address this issue:

1. Stop Operation: Immediately stop the operation of the drive to prevent any potential damage to the equipment and ensure safety.

2. Identify the Cause: Determine the reason for the DC link voltage undervoltage fault. Common causes include:

   • Insufficient power supply voltage or fluctuations in the mains power.
   • Faulty components within the drive, such as capacitors or power modules.
   • Overloading of the drive beyond its rated capacity.
   • Loose connections or damaged wiring within the drive or power supply system.

3. Inspect Power Supply: Check the power supply voltage and ensure that it is within the acceptable range specified for the SINAMICS G120 drive. Verify that there are no voltage drops or fluctuations that could cause the undervoltage condition.

4. Review Drive Parameters: Verify the configuration settings and parameterization of the SINAMICS G120 drive. Ensure that the drive's settings are appropriate for the connected motor and application. Adjust parameters related to voltage limits and protection thresholds if necessary.

5. Check Components: Inspect the drive components, including capacitors, power modules, and control boards, for any signs of damage or malfunction. Replace any faulty components identified during the inspection.

6. Inspect Wiring and Connections: Examine the wiring and connections between the drive, motor, and power supply system. Ensure that all connections are secure and properly tightened. Look for any signs of loose connections, damaged cables, or overheating.

7. Monitor Voltage: Use the diagnostic tools provided by the drive to monitor the DC link voltage during operation. Analyze the voltage waveform and trends to identify any irregularities or drops that could indicate an undervoltage condition.

8. Implement Protective Measures: Consider implementing additional protective measures such as voltage stabilizers or uninterruptible power supplies (UPS) to mitigate the risk of DC link voltage undervoltage faults.

9. Perform Test Runs: Conduct test runs with the drive and motor system under different operating conditions to verify that the undervoltage issue has been resolved. Monitor the DC link voltage closely and observe the performance of the drive system.