fieldoriented

Field-oriented control, also known as vector control, is a method for controlling AC motors by decoupling torque and flux generation. It does so by transforming the motor currents from a stationary three-phase reference frame into a two-axis rotating reference frame aligned with the rotor flux. In the d-q frame, current components i_d and i_q correspond to flux-producing and torque-producing effects, respectively. A position or speed sensor (or a sensorless estimator) provides the rotor angle to maintain alignment between the rotating frame and the rotor flux.

Implementation uses Clarke and Park transformations to convert three-phase currents to the d-q frame and back, plus PWM control of a power inverter. Reference currents for i_d and i_q are generated by a control loop, typically using proportional-integral controllers, to regulate torque and flux. The resulting voltages are applied to the motor windings to achieve fast, smooth torque response across a broad speed range.

Field-oriented control is widely used with induction motors, permanent magnet synchronous motors, and synchronous reluctance motors. Benefits include decoupled torque and flux control, improved dynamic performance, higher efficiency, and a wider operating speed range, including field-weakening at high speeds. Drawbacks include sensitivity to motor parameter variations, model inaccuracies, and the need for precise rotor position information or robust estimators, which increases system complexity and cost.

Applications span industrial drives, servo systems, robotics, and electric traction in vehicles. Advancements include sensorless FOC, improved estimators, and real-time optimization to reduce losses and electromagnetic interference.