Scalar Control of Induction Motors

Abstract

A majority of the existing variable speed drive systems with induction motors are low-performance drives in which the adjusted variables are the magnitude and frequency of either the voltage or current supplied to the stator. This allows control of the steady-state speed or torque of the motor, while the magnetic field in the motor is kept at a constant, desired level. This type of control is usually referred to as scalar control, since the controlled stator voltage or current are assumed sinusoidal, with only the magnitude and frequency adjusted, and with no concern for the spatial position (phase) of the corresponding vector quantities. In contrast, vector control schemes, based on the Field Orientation Principle; provide adjustment of the magnitude and phase of the vector quantities of the motor. In vector-controlled, high-performance drive systems, the instantaneous torque and magnetic field of the motor are regulated, both in the steady-state and under transient operating conditions. Scalar control systems are simpler than those employing vector control, but the superiority of the latter from the point of view of dynamic performance of the drive is unqestionable.

The online version of the original chapter can be found at http://dx.doi.org/10.1007/978-1-4615-2730-5_8