Résumé:
The need to improve the quality and performance of electromechanical drive
control systems is crucial, where the objective is to increase the production quality of
industrial processes and to use rationally our resources. In order to attain this aim, it is
necessary to improve and perfecting all quality performance indices of these systems
and maintaining them at the required level.
Separately excited DC drive speed control systems, especially those used in
rolling mill industries, are characterized by joint elasticity and some aspects of non
linearity. This is mainly due to the long shaft coupling the driving motor and the load,
which causes substantial torsional vibration in case of load side parameters variation of
speed and /or torque changes. These inherent properties can greatly affect the quality
of the rolling material and even influence the stability of the used closed loop control
system.
In case of minor changes of these parameters, their influence on drive dynamic
behavior may be satisfactorily compensated using conventional speed control
algorithms, such as PI controller, and ensuring the required quality and accuracy
performance of the system response. However, the effects of substantial parameter
changes and variations, which is generally the case for this type of application, can no
longer be effectively compensated by these algorithms and it is not possible to obtain
satisfactory performance by applying only standard and conventional PI controllers.
Therefore, looking for control methods and techniques capable of solving the problem
of these applications’ drives and achieving improvement of their performances is
crucial. In this vein, our work consists of applying the proposed Mini-Max
optimization approach in conjunction with other compensation techniques on chosen
system models to improve and perfecting the performances of an already existing PI
speed controller based separately excited DC drive system and increasing thereafter its
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order of astatism under variable operational conditions of set point speed change and
load torque disturbance.
On the other hand, these drives are also equipped with current limiter to protect
against any damage of the drive components when abrupt set point change or load
torque disturbance occur. Unfortunately, the presence of these devices may lead, under
those conditions, to saturation of PI speed controller output and consequent serious
degradation in system performance is evident. Therefore, the effect of inherent
actuator saturation (non-linearity) on degrading the drive’s transient and steady-state
performances is also studied, where the effectiveness and efficiency of the proposed
novel conditional integration anti-windup compensation technique is verified for this
purpose.
