You say PSP games but you posted in the PS2 section. I'll answer regarding both formats.
PSP games are region free- no conversion needed. If you see a game that came out in Japan that isn't coming soon/ at all feel free to hit up an importer or eBay to get it.
As for PlayStation 2 games, they cannot be converted. You can get them to play on your PS2 with a mod chip installed on the system. However, we do not recommend this as we have seen numerous people have their system's life shortened/ killed outright by sloppy install attempts. For this reason i will not be giving any sources for where to obtain one and ask that no one else do the same- the links will be removed if posted.