Welcome to the site!
In order to understand what you're trying to accomplish, I'd like to ask a question, if I may:
Why do you think you'd want to have three PP's powering one track??
A power pack generally is sufficient for a stretch of track on a home layout, that's why i'm asking.
If you are trying to run multiple engines on one track with individual control, then you should look into what's known as DCC or Digital Command Control, which enables that ability to run engines in either direction on the same track, do multi-unit lashups, helper operations, etc.
If you don't want to go into the electronics of DCC, then you can isolate sections of track, and dedicate a PP to each section if you want. Most folks going that way will run the power through switches so they can turn sections on and off and "park" engines (and their trains) while they pay attention to the live sections running locos.
I'm sure others will chime in, if you gave us a little more info on what you're trying to do, then we might be able to give you some advice you think you can use.
In the meantime, I hope I answered some or most of your question!!
