High Performance Controllers for Speed and Position Induction Motor Drive using New Reaching Law

The field-oriented control technique has been widely used when high-performance rotary machine drive is required, especially the indirect field oriented control (IFOC) which is one of the most effective vector control of IM due to the simplicity of designing and implementation [1]. Advent of high switching frequency PWM inverters has made it possible to apply sophisticated control strategies to AC motor drives. The space vector modulation (SVM) technique has become one of the most important PWM methods. It appears to be the best alternative for a three phase switching power converter because it provides an optimization of converter operation; reducing the commutations of the power semiconductor, does not generate subharmonic components, with capacity about 90.6% of DC link exploitation, and it becomes the best technique to reduce the ripple in the torque signal [2].

However the classical proportional-integral and derivative (PID) controller’s which are the main control tool being used in AC machine drives, have major drawbacks that are the sensitivity to the system-parameters variations and bad rejection of external disturbances. To surmount these drawbacks and improve the induction motor control techniques, a set of papers are presented in the literature, we cite as non exhaustive examples; the fuzzy and neuro-fuzzy control [3,4], the neural network control [5], the sliding mode control [6], and the neuro-fuzzy-sliding mode control [7].

All of aforementioned techniques present a good performances, but in term of fast response and robustness against uncertainties including; parametric variations, external disturbance rejection, and unmodelled dynamics, the sliding mode controllers is computationally simple compared to adaptive controllers with parameter estimation and have the advantage and best high results that leads to the improvement of IM control [8].

The SMC was firstly investigated for electric motors by Utkin [9], its design method is generally based on two steps, first, the selection of an appropriate sliding surface, and second, the synthesis of a control law such that a reaching condition is satisfied which makes the selected surface attractive, then, that evolves two modes; reaching mode and sliding mode. Nevertheless, before attaining the sliding surface (i.e. reaching mode), the system cannot dominate the variations in parameters and external disturbances, thus making weak robustness of the system [10].

It is a well known opinion that the major drawback of sliding mode control is the chattering phenomenon. The chattering consists of the oscillation of the control signal, tied to the discontinuous nature of the control law, at a frequency and amplitude which cannot be tolerated in some practical applications, especially mechanical and electro-mechanical ones, also this harmful phenomenon, is caused by unmodeled dynamics or discrete time implementation [11]. A large number of works deals to reduce the chattering have been developed, first of them consist of a soft continuous approximation of the discontinuous law, when boundary layer of definite width on both sides of sliding plane is introduced [12], This method can give a chattering reduction system but a finite steady state error must exist, other works introduce new switching surfaces; as nonlinear and time-varying parabolic sliding surface to improve the discontinuous control law part of a classical sliding mode controller [13], also in [14], the proposed modification consists in modifying the sliding surface using fuzzy rules. These structures make the implementation of controller more complex and affect system convergence to the surface.

The approach, called higher order SMC, has been proposed in order to reduce the chattering phenomenon. Instead of influencing the first sliding variable time derivative, the signum function acts on its higher order time derivative, then the chattering problem is avoided by removing discontinuity from control input. The papers proposed second, and high order controllers respectively in [15,16] but, in spite of chattering attenuation, such methods are overly complex and difficult to implement in practice.

Besides of these works, in last decade a new concept called Reaching Law Method (RLC) had been introduced in sliding mode control [17]. In this method the error dynamics is specified in the reaching mode, with selecting appropriately parameters both the dynamic quality of the SMC system can be controlled and the chattering is removed. Many researchers pay attention to this approach. In [18] authors has applied constant plus proportional rate RLC used in [17] for Permanent Magnet Synchronous Motors PMSM drive system. The results showed that, the proposed method gave fast speed response time, with good rejection of disturbances, but the robustness of the system against parametric uncertainties was not considered. In [19] authors propose an improvement of power rate RLC of the article [17], according th

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