参数是固定位置，因此您不能仅将format参数放在文件名旁边。您需要执行以下操作：

The arguments are positional so you can't just put the format argument next to the filename. You'll need to do something like the below:

$ excel.workbooks.open（ $ input，$ null，$ null， '4'）

但是，正如@DavidBrabant所说，使用 Import-Csv可能会更好

However, as @DavidBrabant says, you'd probably be better off using Import-Csv