Parametric Optimization of PI Speed Regulators and State Observer based Control Systems with Viscous Friction Coefficient Account using Mini-Max Approach

Abstract

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 iii 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.