Rav Chaim Yaakov Goldvicht ZT"L (Rosh Yeshiva of Kerem B'Yavneh) had an interesting explanation. For 20 years he was bothered by the question - for years, Yosef served as viceroy of Egypt, and sent no message to his father to tell him he was alive, and made no attempt to contact him. Why not? He gave the following explanation:
Yosef thought that his brothers had sold him as their own decision, but surely his father was looking for him. He spends 2 years in Egyptian prison, telling the cup-bearer (Bereishis 40:15) that he should help him get out of prison since he was stolen from his homeland (implying he wants to get back). Then, he gets out of prison, and names his children in thanks to G-d for helping him forget his father's household (Bereishis 41:51) and for making him successful in Egypt (Bereishis 41:52)! What happened between was Pharaoh's dreams. Yosef saw in these dreams, in addition to the message to Pharaoh, a prophecy being sent to him. In the dream, he saw the 7 cows which were יפות מראה (Bereishis 41:2) get devoured by the 7 cows that were דקות (Bereishis 41:3), and one can't help but notice that וְעֵינֵי לֵאָה רַכּוֹת וְרָחֵל הָיְתָה יְפַת תֹּאַר וִיפַת מַרְאֶה (Bereishis 29:17). Yosef saw for himself a message in the dream, that the sons of Leah were to overcome and vanquish the sons of Rachel, who was יפת מראה. And then Yosef thought of how Yaakov had sent him to go find his brothers, despite Yaakov no doubt being aware of how they harbored hatred against him. And Yosef noted that in every generation of this Chosen people, there had been a chosen son and a rejected son - Avraham had cast away Yishma'el, and Eisav was cut out of the family in the following generation. Perhaps the children of Rachel were the next to be pruned out.
Then he sees his brothers arrive. And who is missing? None other than Binyomin, the other son of Rachel! Yosef assumes he must have been cast away as well, and he arranges to find out. Upon discovering that Binyomin is still around, Yosef decides it is his responsibility to get Binyomin away from them. So he arranges to have them bring Binyomin down, and then has Binyomin siezed in such a way that it seems to be his own fault. The brothers have only to let him go, since it is his own fault for stealing. After all, like mother like son ([see Rashi to Bereishis 31:33).
But to his surprise, Yehuda steps up and offers himself in Binyomin's stead! Not only that, but he has actually put his own life on the line for Binyomin's safety (Bereishis 44:32), and their father is very concerned with Binyomin's well-being (Bereishis 44:20). Yosef's notions are shattered, he sees that there was no conspiracy against the family of Rachel, and he reveals himself.
I heard this from talmidim of R' Goldvicht, but it can be found in אסופת מערכות.