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.

**source**

http://www.jcee.upc.es/JCEE2001/PDFs%202000/

8arias.pdf