The function below adds a BusLogic SCSI controller to a guest.

The prerequisite for the function to work correctly is that there are no devices with the same "key" defined on the guest.
The function could be elaborated with a test that loops through the current devices and checks if the key is free.
Something like the functions I showed in Re: Changing Disk Persistence

function add-SCSIController {
  param($VMname)
 
  $vm = Get-View (Get-VM $VMname).ID
 
  $spec = New-Object VMware.Vim.VirtualMachineConfigSpec
  $spec.deviceChange = @()
  $spec.deviceChange += New-Object VMware.Vim.VirtualDeviceConfigSpec
 
  $spec.deviceChange[0].device = New-Object VMware.Vim.VirtualBusLogicController
  $spec.deviceChange[0].device.busNumber = 0
  $spec.deviceChange[0].device.ControllerKey = 100
  $spec.deviceChange[0].device.DeviceInfo = New-Object VMware.Vim.Description
  $spec.deviceChange[0].device.DeviceInfo.label = "SCSI Controller 0"
  $spec.deviceChange[0].device.DeviceInfo.summary = "BusLogic"
  $spec.deviceChange[0].device.hotAddRemove = $TRUE
  $spec.deviceChange[0].device.key = 1000
  $spec.deviceChange[0].device.scsiCtlrUnitNumber = 7
  $spec.deviceChange[0].device.sharedBus = "noSharing"
  $spec.deviceChange[0].operation = "add"
 
  $vm.ReconfigVM_Task($spec)
}
 
Add-SCSIController("HORSE")
 
Get-VM "HORSE" | New-HardDisk -CapacityKB 10240