Forcefully Stop HyperV VM

Get the name as displayed in HyperV of the VM you want to stop and then run:

$VMGUID = (Get-VM "vm_name").ID
$VMWMProc = (Get-WmiObject Win32_Process | ? {$_.Name -match 'VMWP' -and $_.CommandLine -match $VMGUID})
Stop-Process ($VMWMProc.ProcessId) -Force