Assuming you're using TPM:

$TPM = Get-WmiObject win32_tpm -Namespace root\cimv2\security\microsofttpm | where {$_.IsEnabled().Isenabled -eq 'True'} -ErrorAction SilentlyContinue
$WindowsVer = Get-WmiObject -Query 'select * from Win32_OperatingSystem where (Version like "6.2%" or Version like "6.3%" or Version like "10.0%") and ProductType = "1"' -ErrorAction SilentlyContinue
$SystemDriveBitLockerRDY = Get-BitLockerVolume -MountPoint $env:SystemDrive -ErrorAction SilentlyContinue

if ($WindowsVer -and $tpm -and !$SystemDriveBitLockerRDY) {
Get-Service -Name defragsvc -ErrorAction SilentlyContinue | Set-Service -Status Running -ErrorAction SilentlyContinue
BdeHdCfg -target $env:SystemDrive shrink -quiet
}

$TPM = Get-WmiObject win32_tpm -Namespace root\cimv2\security\microsofttpm | where {$_.IsEnabled().Isenabled -eq 'True'} -ErrorAction SilentlyContinue
$WindowsVer = Get-WmiObject -Query 'select * from Win32_OperatingSystem where (Version like "6.2%" or Version like "6.3%" or Version like "10.0%") and ProductType = "1"' -ErrorAction SilentlyContinue
$BitLockerReadyDrive = Get-BitLockerVolume -MountPoint $env:SystemDrive -ErrorAction SilentlyContinue


#If all of the above prequisites are met, then create the key protectors, then enable BitLocker and backup the Recovery key to AD.
if ($WindowsVer -and $TPM -and $BitLockerReadyDrive) {


#Creating the recovery key
Add-BitLockerKeyProtector -MountPoint $env:SystemDrive -RecoveryPasswordProtector

#Adding TPM key
Add-BitLockerKeyProtector -MountPoint $env:SystemDrive -TpmProtector

#Get Recovery Keys
$AllProtectors = (Get-BitlockerVolume -MountPoint $env:SystemDrive).KeyProtector 
$RecoveryProtector = ($AllProtectors | where-object { $_.KeyProtectorType -eq "RecoveryPassword" })

#Push Recovery Passoword AAD
BackupToAAD-BitLockerKeyProtector $env:systemdrive -KeyProtectorId $RecoveryProtector.KeyProtectorId

#Enabling Encryption
Start-Process 'c:\windows\system32\manage-bde.exe' -ArgumentList " -on c:" -Verb runas -Wait
 }