Com o seu link fornecido na seção de comentários ...
Crie um script PS ou execute as seguintes linhas diretamente no PowerShell:
# load assembly System.Windows.Forms which will be used
Add-Type -AssemblyName System.Windows.Forms
# set powerstate to suspend (sleep mode)
$PowerState = [System.Windows.Forms.PowerState]::Suspend;
# do not force putting Windows to sleep
$Force = $false;
# so you can wake up your computer from sleep
$DisableWake = $false;
# do it! Set computer to sleep
[System.Windows.Forms.Application]::SetSuspendState($PowerState, $Force, $DisableWake);