generate_vm_xml_config.ps1

[CmdletBinding()]
param(
	[Parameter(Mandatory)]
	[string]$VMName,

	[Parameter(Mandatory)]
	[string]$OutputFile
)

function Get-DriveType($drive)
{
	if($drive -is [Microsoft.HyperV.PowerShell.HardDiskDrive])
	{
		return "VHD"
	}

	if($drive -is [Microsoft.HyperV.PowerShell.DvdDrive])
	{
		return "ISO"
	}

	return "NONE"
}

function Get-Drives([Microsoft.HyperV.PowerShell.Drive[]]$drives)
{
	$drives | ForEach-Object {
		$num = $_.DiskNumber + 0
		@"
<drive$num>
		<pathname type="string">$($_.Path)</pathname>
		<type type="string">$(Get-DriveType($_))</type>
</drive$num>
"@
	}
}

function Get-IdeControllers($vm)
{
	 Get-VMIdeController -VM $vm | ForEach-Object {	
		 
		@"
<controller$($_.ControllerNumber)>
		 $(Get-Drives($_.Drives))
</controller$($_.ControllerNumber)>
"@
	}
}

function Get-ScsiControllers($vm)
{
	 Get-VMScsiController -VM $vm | ForEach-Object {	
				 
		@"		 
<controller$($_.ControllerNumber)>
		 $(Get-Drives($_.Drives))
</controller$($_.ControllerNumber)>
"@
	}
}

function Get-Controllers($vm)
{
	if($vm.Generation -eq 1)
	{
		Get-IdeControllers($vm)
	}
	else
	{
		"<scsi ChannelInstanceGuid=`"x`">$(Get-ScsiControllers($vm))</scsi>"
	}
}

$vm = Get-VM -Name $VMName

$adapter = Get-VMNetworkAdapter -VM $vm | select -First 1

if($vm.Generation -eq 1)
{
	$bios = Get-VMBios -VM $vm
	$startupOrder = $bios.StartupOrder
}
else
{
	$firmware = Get-VMFirmware -VM $vm
	$startupOrder = $firmware.BootOrder
}

$xml = [xml]@"
<?xml version="1.0" ?>
<configuration>
	<properties>
		<subtype type="integer">$($vm.Generation - 1)</subtype>
		<name type="string">$($vm.Name)</name>
	</properties>
	<settings>
		<processors>
			<count type="integer">$($vm.ProcessorCount)</count>
		</processors>
		<memory>
			<bank>
				<dynamic_memory_enabled type="bool">$($vm.DynamicMemoryEnabled)</dynamic_memory_enabled>
				<limit type="integer">$($vm.MemoryMaximum / 1MB)</limit>
				<reservation type="integer">$($vm.MemoryMinimum / 1MB)</reservation>
				<size type="integer">$($vm.MemoryStartup / 1MB)</size>
			</bank>
		</memory>
	</settings>
	<AltSwitchName type="string">$($adapter.SwitchName)</AltSwitchName>
	<boot>
		<device0 type="string">Optical</device0>
	</boot>
	<secure_boot_enabled type="bool">False</secure_boot_enabled> <!-- TODO -->
	<notes type="string">$($vm.Notes)</notes>
	<vm-controllers>
		$(Get-Controllers($vm))
	</vm-controllers>
</configuration>
"@

$xml.Save($OutputFile)

@cmosh, I also encounter the drive conversion issue as @ForNeVeR, but in the SCSI section. When I initially set up my VM, I was able to run this against it. Only after I deleted, then imported that VM, and THEN ran this script against the VM did I actually run into this problem.

Get-Drives : Cannot process argument transformation on parameter 'drives'. Cannot convert the "HardDiskDrive (Name = 'Hard Drive on SCSI controller number 0 at location 0', VMName = 
ubuntu1604tcbase') [Id = 'Microsoft:540EFF01-0895-458E-806D-C8FD06101DF2\FA75C42E-2490-4D4C-98F1-7C7D82455EE4\0\0\D', VMId = '540eff01-0895-458e-806d-c8fd06101df2']" value of type 
"Microsoft.HyperV.PowerShell.HardDiskDrive" to type "Microsoft.HyperV.PowerShell.Drive".
At <mypath>\generate_vm_xml_config.ps1:56 char:16
+          $(Get-Drives($_.Drives))
+                      ~~~~~~~~~~~
    + CategoryInfo          : InvalidData: (:) [Get-Drives], ParameterBindingArgumentTransformationException
    + FullyQualifiedErrorId : ParameterArgumentTransformationError,Get-Drives

I'm going to do some more troubleshooting, will let you know if I figure it out.

How-to use it ?