使用Powershell将SQL Server实例添加到中央管理服务器组

I am trying to create a script to automatically iterate through a text file of all our SQL Server instances and add each on if it doesn't already exist to the CMS. I want to try doing this through SMO instead of hardcoding sql strings in. Below is what I have so far but it doesn't seem to be working. Any help would be appreciated. Thanks.I am trying to create a script to automatically