Powershell script to prevent Windows from sleeping

dontsleep.ps1

param([int]$minutes=60)  # input param, 60 minutes if no value provided

$wsh = New-Object -ComObject WScript.Shell
$a = Get-Date # Current time
$b = $a.AddMinutes($minutes) # Target time

while ($a -lt $b) {
# Send Shift+F15    
$wsh.SendKeys('+{F15}')
    Start-Sleep -seconds 240  # sleep for 4 minutes
    $a = Get-Date
}

# Use it with: powershell.exe -file dontsleep.ps1 -minutes 20