Vector control , also called field-oriented control FOC , is a variable-frequency drive VFD control method in which the stator currents of a three-phase AC electric motor 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 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.
However, it is becoming increasingly attractive for lower performance applications as well due to FOC's motor size, cost and power consumption reduction superiority. Hasse and Siemens' F. Blaschke pioneered vector control of AC motors starting in and in the early s. Hasse in terms of proposing indirect vector control, Blaschke in terms of proposing direct vector control.
Yet it was not until after the commercialization of microprocessors , that is in the early s, that general purpose AC drives became available.
The Park transformation has long been widely used in the analysis and study of synchronous and induction machines. The transformation is by far the single most important concept needed for an understanding of how FOC works, the concept having been first conceptualized in a paper authored by Robert H. The novelty of Park's work involves his ability to transform any related machine's linear differential equation set from one with time varying coefficients to another with time invariant coefficients.
While the analysis of AC drive controls can be technically quite involved "See also" section , such analysis invariably starts with modeling of the drive-motor circuit involved along the lines of accompanying signal flow graph and equations.
Sensorless vector control ppt to pdf
In vector control, an AC induction or synchronous motor is controlled under all operating conditions like a separately excited DC motor. Vector control accordingly generates a three-phase PWM motor voltage output derived from a complex voltage vector to control a complex current vector derived from motor's three-phase stator current input through projections or rotations back and forth between the three-phase speed and time dependent system and these vectors' rotating reference-frame two- coordinate time invariant system.
Such complex stator current space vector can be defined in a d,q coordinate system with orthogonal components along d direct and q quadrature axes such that field flux linkage component of current is aligned along the d axis and torque component of current is aligned along the q axis.
Components of the d,q system current vector allow conventional control such as proportional and integral, or PI, control , as with a DC motor. Projections associated with the d,q coordinate system typically involve:   .
However, it is not uncommon for sources to use three-to-two, a,b,c -to- d,q and inverse projections. While d,q coordinate system rotation can arbitrarily be set to any speed, there are three preferred speeds or reference frames: . Decoupled torque and field currents can thus be derived from raw stator current inputs for control algorithm development.
Whereas magnetic field and torque components in DC motors can be operated relatively simply by separately controlling the respective field and armature currents, economical control of AC motors in variable speed application has required development of microprocessor-based controls  with all AC drives now using powerful DSP digital signal processing technology. There are two vector control methods, direct or feedback vector control DFOC and indirect or feedforward vector control IFOC , IFOC being more commonly used because in closed-loop mode such drives more easily operate throughout the speed range from zero speed to high-speed field-weakening.
In IFOC, flux space angle feedforward and flux magnitude signals first measure stator currents and rotor speed for then deriving flux space angle proper by summing the rotor angle corresponding to the rotor speed and the calculated reference value of slip angle corresponding to the slip frequency.
Sensorless control requires derivation of rotor speed information from measured stator voltage and currents in combination with open-loop estimators or closed-loop observers. Stator phase currents are measured, converted to complex space vector in a,b,c coordinate system. Transformed to a coordinate system rotating in rotor reference frame, rotor position is derived by integrating the speed by means of speed measurement sensor.
While PI controllers can be used to control these currents, bang-bang type current control provides better dynamic performance. PI controllers provide d,q coordinate voltage components. A decoupling term is sometimes added to the controller output to improve control performance to mitigate cross coupling or big and rapid changes in speed, current and flux linkage.
PI-controller also sometimes need low-pass filtering at the input or output to prevent the current ripple due to transistor switching from being amplified excessively and destabilizing the control. However, such filtering also limits the dynamic control system performance.
Also the current sensors need not be the best in the market. Thus the cost of the processor and other control hardware is lower making it suitable for applications where the ultimate performance of DTC is not required.
From Wikipedia, the free encyclopedia. Archived from the original on February 16, Archived from the original on June 21, Retrieved April 22, Retrieved May 16, Texas Instruments.
June Retrieved 9 May Retrieved 18 April Amsterdam: Academic. March—April IA 2 : Oct 23—24, Retrieved May 23, Electric Power Systems Research.
Espoo: Helsinki University of Technology. Aug Proceedings of the IEEE. Retrieved June 3, Appliance Magazine. Archived from the original on 7 April Retrieved June 4, Microprocessor-based control systems. Reidel Publishing.
Tennessee Technological University. Electric motors. AC motor DC motor. Repulsion Universal.
AC asynchronous induction IM. Doubly-fed Linear Servomotor Stepper Traction. Electrostatic Piezoelectric Ultrasonic. Hermetic TEFC. Timeline of the electric motor Ball bearing motor Barlow's wheel Lynch motor Mendocino motor Mouse mill motor.
Vector control (motor)
Coilgun Railgun Superconducting machine. Alternator Electric generator Inchworm motor.
SI electromagnetism units. Categories : Electric motors.
GS4 VFD - V/Hz vs Sensor-less Vector