You can reboot a host by using its corresponding view object.
Verify that you are connected to a vCenter Server system.
Use the Get-VMHost cmdlet to get a host by its name, and pass the result to the Get-View cmdlet to get the corresponding view object.
$vmhostView = Get-VMHost -Name Host | Get-View
Call the reboot method of the host view object to reboot the host.
$vmhostView.RebootHost()