27-06-2011, 04:40 PM
Abstract:
During a long time, permanent magnet synchronous motor (PMSM) were only reserved for some
specific applications, however, recently, these machines are becoming more used due to the powerful magnetic
characteristic of the rare earth, being used in different areas. Recently several researchers have proposed
implementations combining the use of permanent magnet synchronous motor with the direct torque control (DTC)
technique offering a quick and precise control. The present work combines these techniques and it proposes the use
of pulse width modulation by means of diverse fuzzy logic strategies to reduce the ripple and to improve flux and
torque response. Simulations are carried comparing the results obtained with the different fuzzy scheme proposed
to solve the problem.
Key-Words: - Permanent magnet synchronous motor, Direct torque control, Pulse width modulation, Fuzzy
control.
1 Introduction
During the last decade, permanent magnet
synchronous motors have been used widely in the
industry to replace classic DC motors and induction
machines (IM), like in paper mills, where power
ranges are common. The main characteristics of these
motors are the low inertia, the high efficiency, power
density and reliability. Being this power density
higher than one of induction motor with the same
ratings due to the no stator power dedicated to the
magnetic field production. Also it is designed not only
to be more powerful but also with lower mass and
lower moment inertia. Due to these advantages, the
permanent magnet synchronous motors are ideal for
the applications where a quick accurate torque control,
low resolution position sensors is required,
considering its performance and cost minimization.
For the induction machines, there have been
developed methods to control the electromechanical
torque in an indirect way using spatial vectors and
transformations to the system of oriented field [1]. By
means of these techniques it is possible to reproduce
the behavior of the classical DC machines. The main
limitations of this method are that it depends on the
parameters of the machine to carry out the
transformations, as well as of a wide capacity of
control calculation and the necessity of position
sensors for the rotor, increasing the costs of the total
system.
The strategy proposed of Direct Torque Control for
the induction machines [2], it reduces the dependence
of the parameters of the machine and improves
considerably the system dynamics and has become an
accepted control method beside the field oriented
control. The DTC was first applied to asynchronous
machines and later to synchronous machine. This
technique compares by means of a hysteresis band the
flow and the torque with its respective references and
it selects form a vectors tables the commutation state
of the inverter bridge that will correct the error.
The three-phase inverter bridge has only six active
states, which gives to the control system a
"bang-bang" behavior with a marked ripple. To solve
this problem it has been proved techniques that try to
modulate the vector size selected from commutation
table by pulse width modulation, being able this to
reduce the ripple.
The idea of combining the advantages of DTC in
PMSM were presented in the ‘90 [3], [4], and from
then many authors have proposed diverse applications
to improve this technique.
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