Frank Gill has written a script to perform an Availability Group failover using Powershell:
The function takes a replica name as input and queries system tables for Availability Groups running as secondary that are online, healthy, and synchronous. For each AG found, the function generates an ALTER AVAILABILITY GROUP statement. If the -noexec parm is set to 0, the command will be executed. If -noexec is set to 1, the command will be written out to a file.
When writing the function, I started out trying to use the native PowerShell Availability Group cmdlets. After several false starts, I found it easier to develop the T-SQL code in Management Studio and use Invoke-Sqlcmd to execute the code. The code is available below. I hope you can put it to use.
Click through for the script.