The induction motors are very common because they are inexpensive and robust, finding use in
everything from industrial applications such as pumps, fans, and blowers to home appliances.
Traditionally, induction motors have been run at a single speed, which was determined by the
frequency of the main voltage and the number of poles in the motor. Controlling the speed of an
induction motor is far more difficult than controlling the speed of a DC motor since there is no
linear relationship between the motor current and the resulting torque as there is for a DC motor.
The technique called vector control can be used to vary the speed of an induction motor over a
wide range. It was initially developed by Blaschke (1971-1973). In the vector control scheme, a
complex current is synthesised from two quadrature components, one of which is responsible for
the flux level in the motor, and another which controls the torque production in the motor.
Essentially, the control problem is reformulated to resemble the control of a DC motor. Vector
control offers a number of benefits including speed control over a wide range, precise speed
regulation, fast dynamic response, and operation above base speed.
The vector control algorithm is based on two fundamental ideas. The first is the flux and torque
producing currents. An induction motor can be modelled most simply (and controlled most simply)
using two quadrature currents rather than the familiar three phase currents actually applied to the
motor. These two currents called direct (Id) and quadrature (Iq) are responsible for producing flux
and torque respectively in the motor. By definition, the Iq current is in phase with the stator flux,
and Id is at right angles. Of course, the actual voltages applied to the motor and the resulting
currents are in the familiar three-phase system. The move between a stationary reference frame and
a reference frame, which is rotating synchronous with the stator flux, becomes then the problem.
This leads to the second fundamental idea behind vector control.
The induction motors are very common because they are inexpensive and robust, finding use ineverything from industrial applications such as pumps, fans, and blowers to home appliances.Traditionally, induction motors have been run at a single speed, which was determined by thefrequency of the main voltage and the number of poles in the motor. Controlling the speed of aninduction motor is far more difficult than controlling the speed of a DC motor since there is nolinear relationship between the motor current and the resulting torque as there is for a DC motor.The technique called vector control can be used to vary the speed of an induction motor over awide range. It was initially developed by Blaschke (1971-1973). In the vector control scheme, acomplex current is synthesised from two quadrature components, one of which is responsible forthe flux level in the motor, and another which controls the torque production in the motor.Essentially, the control problem is reformulated to resemble the control of a DC motor. Vectorcontrol offers a number of benefits including speed control over a wide range, precise speedregulation, fast dynamic response, and operation above base speed.The vector control algorithm is based on two fundamental ideas. The first is the flux and torqueproducing currents. An induction motor can be modelled most simply (and controlled most simply)using two quadrature currents rather than the familiar three phase currents actually applied to themotor. These two currents called direct (Id) and quadrature (Iq) are responsible for producing fluxand torque respectively in the motor. By definition, the Iq current is in phase with the stator flux,and Id is at right angles. Of course, the actual voltages applied to the motor and the resultingcurrents are in the familiar three-phase system. The move between a stationary reference frame anda reference frame, which is rotating synchronous with the stator flux, becomes then the problem.This leads to the second fundamental idea behind vector control.
การแปล กรุณารอสักครู่..
