To run a backup from command line you need to run WBadmin
The Technet article for this is here
To configure a regularly scheduled backup, you must be a member of the Administrators group. To perform all other tasks with this command, you must be a member of the Backup Operators or the Administrators group, or you must have been delegated the appropriate permissions.
Backing up your C: drive to the E: Drive, intending on a bare metal recovery, including system state with no prompts to the user.
wbadmin start backup -backupTarget:E: -include:C: -allcritical -systemstate -quiet