Jay,

Before you dive into the control aspects of your converter, make sure you have thought through the physics of your proposal. You are asking for a constant power at the input and constant voltage at the output. I assume you want to regulate the output voltage because the load will vary. As the load varies with output voltage held constant, the output power will vary. The only way you can vary output power without varying input power is to vary the efficiency. Is that really what you want to do?

If you want to control input power only at a very high frequency while you control output voltage at a very low frequency, you might be able to come up with an appropriate control scheme but why not just use an input filter if that's what you have in mind?

Look at it from an input power in versus output power out standpoint. It really doesn't matter how many converters, switches or control loops you include between the input and output, you still have the problem of varying the efficiency of the overall system if you want to control both input power and output voltage. Do you care about efficiency?

Jay,

You're not answering my question about efficiency, but if I were to deduce one from your entries, I'd say you don't care about the efficiency of your proposed system. OK.

Do you want to control input power independent of output voltage? If not, then why do you need these two control loops? If you do want independent controls, then given that the output power can only be less than or equal to the input power, what do you plan to do with the excess power?  I must be missing something.

I'll back out of this discussion at this point and give someone else a chance to help. Good luck.