Sunday, April 5, 2009

Types of Induction Motor Drive Controllers

There are many different ways to drive an induction
motor. The main differences between them are the
motor’s performance and the viability and cost in its
real implementation.

1.1- Voltage/Frequency:
Despite the fact that V/F is the simplest controller, it
is the most widespread, reaching approximately 90%
of the industrial applications. It is known as a scalar
control and acts imposing a constant relation between
voltage and frequency. The structure is very simple
and it is normally used without speed feedback.
However, this controller doesn’t achieve a good
accuracy in both speed and torque responses mainly
due to the fact that the stator flux and the torque are
not directly controlled. Even though, as long as the
parameters are identified, the accuracy in the speed
can be 2% (except in a very low speed) and the
dynamic response can be approximately around 50ms

1.2- Vector Controllers:
In these types of controllers, there are control loops
for controlling both the torque and the flux . The
most spread controllers are the ones that use vector
transform such as either Park or Ku. Its accuracy can
reach values such as 0.5% regarding the speed and
2% regarding the torque, even in stand still.
The main disadvantages are the huge computational
capability required and the compulsory good
identification of the motor parameters.

1.3- Field Acceleration Method:
This method is based on maintaining the amplitude
and the phase of the stator current constants, avoiding
electromagnetic transients. Therefore the equations
used can be simplified saving the vector
transformation in the controllers.
It is achieved some computational reduction,
overcoming the main problem in the vector
controllers and then becoming an important
alternative for the vector controllers.


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