There is quite a lot of material on POW and internees in Australia to be found at the Melbourne branch of National Archives Australia. The basic material has been digitised and is available at:http://www.naa.gov.au/collection/using/search/
You do not need to register as a user. Just click on the box "Begin your Search" and enter the name you want to investigate. The basic records come up under the Series numbers MP1103/1 and MP1103/2.
If you want to do more general research, not for just a single name, the procedure is more difficult and time-consuming. The series contains 42358 individual files, as it covers both prisoners of war and civilian internees (including wives and children in family camps), not only German, but also Italian (the largest number), Japanese, Chinese, Javanese, Russians, Finns, Hungarians, Roumanians, seaman deserters from some dozen countries, including the USA. You need some experience and a lot of dedication to handle material at that level.
As a guide: The numbers all contain five digits, and the prefixes vary. PWG41+ are almost all Afrika-Korps, some Luftwaffe from the Middle East, and a few from Greece and Crete. PWGA42+ contain Kormoran crew (also a few PWDA41+ numbers). PWGM88+ are Ramses crew. (M = Merchant navy.)
The person who provided the "protected personnel" document obviously does not want to be identified, so I shall not give the name of his father, but it took me about five minutes to identify his father, because I know how to work these documents. Just to confirm this: he was Austrian, born 4 February 1916, by trade Schlosser, captured in Greece.
There are also records in the series A367 of those who applied to remain in or return to Australia. These are Commonwealth Security Service files (handed over by ASIO). They are not digitised, and most have not been opened to the public, not because they are classed as secret, but because nobody has applied to see them. (Not many people know of their existence.)