Scalar and vector: a simplified treatment of induction motor control performance

High performance drive applications require fast torque response. Modern advances in brushless AC drives have produced controllers combining good steady state performance with excellent transient behaviour. This is possible with vector control (also termed field oriented, flux vector, etc.). This paper avoids a heavily mathematical treatment and instead gives an appreciation of the basic concepts, comparing the behaviour of an induction machine drive with vector control to that given with other methods of control, here termed scalar control. A versatile simulation package is used to contrast the behaviour, since the differences in behaviour under idealised conditions is extremely helpful in aiding understanding. Some fundamental ideas are first reviewed, such as DC drives and conventional scalar control, with a specific example of the induction motor dynamic performance being given, before vector control is introduced