Direct Torque and Flux Discrete Event Control of
Induction Motors
M´onica E. Romero
Departamento de Electr´onica,
Universidad Nacional de Rosario, Riobamba 245 bis,
(2000) Rosario, Argentina
Email: mromero@fceia.unr.edu.ar
Norbert Giambiasi
LSIS, Universit d’Aix-Marseille III,
Avenue Escadrille Normandie Niemen
13397 Marseille cedex 20 - France
Email: norbert.giambiasi@lsis.org
Abstract—This paper presents a Discrete Event Model (DEVS)
of Direct Torque and Flux Control (DTFC) of an Induction Motor
(IM). DTFC methodology presents two characteristics that makes
the formal discrete event representation necessary. One of them
is the fact that DTFC takes into account the discrete nature of
the actuator, a PWM-inverter, and the other one is that exist an
implicit discretization of the IM model implemented by hysteresis
loops and the quantification of the position of electric magnitudes.
DEVS formalism results a suitable approach to performe analysis
and even more to obtain some improvements in the control
strategy as well as at the simulation level.
I. INTRODUCTION
Direct Flux and Torque Control, is one of the two vectorial
technique of IM which has generated much discussion and
many interesting resuslts comparing with the other vectorial
technique, i.e., Field Oriented Control, [1], [2], [3], [4]. This
control methodology involves a lookup table that specifies
the actuation for each given torque and flux condition. This
method is based on the observation of torque and flux variations
when the different voltage vectors (control signals) are
applied. For this reasons we could say that the synthesis
of the control law is not made in a traditional way, i.e.,
obtaining a control structure pursuing a given methology
and parameterizing it to accomplish a desired performance
index. This characteristic gave rise to many works intended to
develop a control mothodology which gives the output of the
DTFC switching table ([5],[6]).
This technique claims to give control actions according to
the flux and torque conditions, avoiding unnecessary transitions
in the control signal but is very dificult to observe it
from the switching table, moreover, as long as the simulations
and implementations are always made in discrete time, the
mentioned advantage is lost.
One of the main drawback of this methodology is the high
torque ripple. As the control action given by the actuator is
a discontinous signal, (PWM-signal), the IM windings filter
the signal responding to its fundamental component. As the
filtering process is not ideal, attenuated high frequencies components
appear in state variables, (current, flux and torque),
named ripple.
An interesting feature of this control methodology is the fact
that a discretization procedure is carrying on, which means a
discretization of the state space. The control actions are taken
according to this state space partition but using tables with an
informal interpretation.
The main contribution of this work is to propose a formal
representation of the control system (DTFC), that is
to say an unambiguous interpretation of both variables and
operational semantics (the way to simulate or to execute the
model description). We have choosen the DEVS formalism
to accomplish the representation task. The DEVS formalism
has a clean operational semantics and a clean interpretation of
the model elements in the real world. DEVS define a method
of abstraction of dynamic systems that allows building timed
discrete event simulation models (deterministic models) with
a good accuracy.
For the abstraction process, the piecewise constant variables,
obtained after the mentioned discretization procedure, are
transformed into input event trajectories. In this way we
obtain a rigorous specification of the control law which allows
operational analysis and, on the other side, by means of its
associated operational semantic, the posibility of inmediately
simulation as well as real implementations.
Finally, as DEVS is a state variable based model, it is
posible to achieve some improvement at the design control
level respect of the results obtained with the basic strategy.
The paper is organized as follows. Section II presents
the induction motor model employed and a brief description
of both DTFC strategy and DEVS formalism. Sections III
describes the DEVS representation of the DTFC strategy and
Section IV describes the operational mode of DEVS model
of DTFC . Section V presents the DTFC improved strategy.
Section VI presents the simulation code obtainded from the
model specification. Finally, Section VIII summarizes the
paper conclusions.
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