Add Site Collection Admins

cls
 Add-PsSnapin Microsoft.SharePoint.PowerShell

$webApplicationURL = "webapplication URL"
 $group="Domain\GroupName"

$webApp = Get-SPWebApplication $webApplicationURL

if($webApp -ne $null)
 {
 "Web Application : " + $webApp.Name# | Out-File $out -Append

foreach($siteColl in $webApp.Sites)
{ Write-host "Site Collection : " + $siteColl.Url

Write-host $siteColl $site = Get-SPWeb $siteColl.Url $check=$site.EnsureUser($group) | Select $_.UserLogin write-host $check Write-Host " Now adding Domain\GroupName to site collection administrators..." -BackgroundColor DarkGray New-SPUser -UserAlias $check -DisplayName $group -Web $site $User = Get-SPUser -Web $site -Identity $check $user.IsSiteAdmin = $true $user.Update() Write-Host " Added" -ForegroundColor Green
}
}

Remove-PsSnapin Microsoft.SharePoint.PowerShell

Echo Finish

Powershell to Get Users From AD Group

Get-ADGroupMember -identity "GROUPNAME" -Recursive | Get-ADUser -Property DisplayName | Select Name,ObjectClass,DisplayName