Does this site have any protection against abuse of power by moderators? Is there a way we can report their misconducts? For example, for maliciously deleting comments.
See the question on the SE meta: What recourse do I have if I believe a moderator has abused their privileges?
Alternatively for a specific issue see: How do I dispute a moderator's action?
However bear in mind that the physics site runs on good will. People donate their time and expertise for free in the belief that doing so makes the world a better place. The same applies to the moderators. They are not paid for the time and effort they put in. It is exceedingly unlikely a moderator has acted for any reason other than they genuinely believe it is in the best interests of the site.
If you believe a moderator shouldn't have acted in the way they did then post a polite message here explaining the problem and you'll receive polite answers. There is no guarantee that the answers will be to your liking, but at least you'll know exactly why the moderators acted as they did.