Field-oriented control

Article summary

Field-oriented control (FOC), also called vector control, is a variable-frequency drive (VFD) control method in which the stator currents of a three-phase AC motor (like for example BLDC) are identified as two orthogonal components that can be visualized with a vector. One component defines the magnetic flux of the motor, the other the torque. The regulation of magnetic flux in electric drives is sometimes described as flux control, referring to the decoupled control of flux and torque in field-oriented control systems. The control system of the drive calculates the corresponding current component references from the flux and torque references given by the drive's speed control. Typically proportional-integral (PI) controllers are used to keep the measured current components at their reference values. The pulse-width modulation of the variable-frequency drive defines the transistor switching according to the stator voltage references that are the output of the PI current controllers. FOC is used to control AC synchronous and induction motors. It was originally developed for high-performance motor applications that are required to operate smoothly over the full speed range, generate full torque at zero speed, and have high dynamic performance including fast acceleration and deceleration.…

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