Cause : Vdc-max Controller active comes when the inverter is taking steps to manage the DC link voltage and prevent it from exceeding its allowable limits.

A0911 alarm in Siemens Micromaster 420 indicating the Vdc-max controller is active. This means ramp-down times are being extended to prevent overvoltage trips and to keep the DC link voltage within acceptable limits.

1. Check parameter inverter input voltage. 
2. Check ramp-down times.