Scalar control

Scalar control of an AC electrical motor is a way to achieve the variable speed operation by manipulating the supply voltage or current ("magnitude") and the supply frequency while ignoring the magnetic field orientation inside the motor. Scalar control is based on equations valid for a steady-state operation and is frequently open-loop (no sensing except for the current limiter). The scalar control has been to a large degree replaced in high-performance motors by vector control that enables better handling of the transient processes. Low cost and simplicity keeps the scalar control in the majority of low-performance motors, despite inferiority of its dynamic performance; vector control is expected to become universal in the future.