How many ePWM instances are there in a TMS320C28x Piccolo DSP chip?
Each ePWM is a single module, which has two outputs, A and B. For this, each module have ePWMxA and ePWMxB.

These outputs are complementary to each other.

For example, if you use a controller with 8 ePWM modules, You have 16 outputs, grouped in 8 pairs.


  My questions are,
  
  How many ePWM modules are there in one single TMS320C28x Piccolo DSP chip?


You must refer to the datasheet of the controller.


  What does it mean by an ePWM instance? Are those software instances or hardware instances?


Is a hardware instance. This instance has two complementary ouputs, A y B.


  How many ePWM instances are there in one single TMS320C28x Piccolo DSP chip?


You must refer to the datasheet of the controller.

All this is detailed on page 1-3 of "Introduction" chapter, from the reference manual you posted.