# $command_a should be the full path name 
#   of the executable file.
# $command_b should be the actual command.

Your code:
$ppc = Win32::Process::Create(
    $process,
    $command_a, #better? $full_path_to_cmd_exe
    $command_b, #better? $cmd_with_args
    0,
    NORMAL_PRIORITY_CLASS,
    '.'
 );
        
Example from Win32::Process:

$ppc = Win32::Process::Create(
   $ProcessObj,
   "C:/winnt/system32/notepad.exe",
   "notepad temp.txt",
   0,
   NORMAL_PRIORITY_CLASS,
   "."
);