Clink on the link for a very nice overview of how, when and why we use the passive voice.
Click to access when-and-why-passive.pdf
The next link is reference guide to how to use the passive in a large variety of tense constructions. Some of the sentences are not very natural but they do show you how to form a passive sentence in each tense, so they can service as a modal.
For German speakers there is a also a comparison with English and German at the back.
(Adapted from: http://www.englishpage.com/verbpage/activepassive.html)
robertdesenior 