From the principles of electrical engineering it is known that the 3-phase
quantities of the 3-phase AC machines can be summarized to complex
vectors. These vectors can be represented in Cartesian coordinate systems,
which are particularly chosen to suitable render the physical relations of
the machines. These are the field-orientated coordinate system for the 3-
phase AC drive technology or the grid voltage orientated coordinate
system for generator systems. The orientation on a certain vector for
modelling and design of the feedback control loops is generally called
vector orientation.