To eliminate the time-varying inductances, the unified theory applies a mathematical coordinate transformation, often referred to as the or Park's transformation.
For the reader, the "Aha!" moment comes when they realize the torque equation derived in Chapter 2 applies to every machine in the book, just with different variables plugged in. The Unified Theory Of Electrical Machines By C.v. Jones Pdf
The seminal textbook The Unified Theory of Electrical Machines Charles Vincent Jones was first published in Butterworths . Spanning roughly To eliminate the time-varying inductances