What are all the hero reward frags you can obtain from Ace week?

Ace Commander does not award Epic Hero Choice Card IV, those come from the Joy Luck event. AC awards a certain number of hero frags depending on your ranking, and the hero changes every so often. So far I have seen Zephyr and Obsidian as the awarded frags.

Sorry but that's false. You're right in that it isn't IV but always Hero Choice Card VI with the heroes the first answer provided. Zephyr is in Hero Choice Card II along with Phoenix and Lady M, never during Ace though. This card can be acquired by competing in certain events that run when Ace isn't running. And in the the Cube event, which runs during Ace on Thursday I believe.

Both of the previous answers are partially right and partially wrong. When a state first opens, Ace rewards specific hero shards, such as Zephyr or Obsidian (based off memory, I don't recall which event I got my first Zephyr frags from, but I know Obsidian was the Ace reward for a long time) . After a certain amount of time has passed, the rewards are then changed to the Epic Hero Choice Card VI (which grants Obsidian, Nam Hayul, or Atropos frags). As far as the rotation, all I can tell you is what I have experienced.