Some comments or questions that might help:
A. What kind of AC motor? Single phase, 3 phase ....universal or synchronous in that RPM is tied to frequency of supply. Don't get too wrapped up in this but it does make a difference. Note if common single phase you need to worry about the starting circuit if the plan is to vary the speed.
B. By control do you mean just on or off, reverse, variable speed, multi-speed...?
C. If on/off, reverse - more or less switching tasks, are relays sufficient? If so, then PIC to relay is common interface.
D. If variable speed, do you intend to create the variable frequency/variable voltage power supply to go with it - or will the VFD be a separate system? If it is separate - what are the inteface requirements - 4 to 20 ma, 0-10 volts, some kind of serial data transfer?
Lots of questions intended to help you narrow the possibilities.