Field Oriented Control (Vector Control) of 3 Phase Squirrel Cage Induction Motors

Abstract

Vector control, also described as field oriented control, is being increasingly used for the speed control of induction motors. This is because, with vector control, it is possible to achieve high dynamic (transient) performance, equalling that of the separately excited DC motor, in variable speed AC drives. Therefore, vector control makes it possible to use, in place of a DC motor, a 3 phase induction motor, which is smaller, mechanically more sturdy, less expensive, and does not have the commutator or other rubbing contacts, and is therefore free of associated maintenance requirements and sparking problems. Vector control, however, requires on-line computation of certain control variables using inputs from sensing elements which continually sense operating motor variables such as motor line currents, motor shaft position or speed. These computed control variables serve as feedback values, which are compared with the appropriate reference values. The errors are continuously corrected by appropriately del...