Improved Sliding Mode Controller for Maximum Power Point Tracking of WECS
Sami Kahla1,2, Moussa Sedraoui1, Youcef Soufi3, Mohcene Bechouat1
1Telecommunication Laboratory, University 8 Mai 1945 of Guelma, Algeria.
2Research Center in Industrial Technologies, CRTI, P.O. Box 64, 16014 Cheraga, Algiers, Algeria.
3Labget laboratory, University of Tebessa, Algeria.
Abstract
Due to the major discrepancy between the exigent demands regarding the electrical energy quality and the irregular characters of the wind, which is characterized by a random and instantaneous speed variation, it is suitable to determine the optimal operating point that maximizes as much as possible the efficiency of the obtained electrical energy in the grid. The present paper deals with the above-mentioned problem by introducing an additional low-frequency component in the standard sliding mode control strategy. The purpose is to maximize the power point tracking of wind energy and to reduce the mechanical loads where the variable wind speed is considered. This idea has the ability to drive the conversion system to the optimal operating point by which the switched component problem, commonly called also the chattering problem of the standard sliding mod control strategy that should be solved. To examine the validity of the proposed idea, the obtained results are compared with those given by the standard sliding mode control strategy wherein our method can ensure a better dynamic behavior of the wind energy conversion system.
Keywords: . Maximum Power Point Tracking MPTT. Standard and Improved Sliding mode controller, Induction Generator IG.
Received: September 21, 2017 To cite this article:
Sami Kahla, Moussa Sedraoui, Youcef Soufi, Mohcene Bechouat, “Improved Sliding Mode Controller for Maximum Power Point Tracking of WECS”, in Electrotehnica, Electronica, Automatica (EEA), 2018, vol. 66, no.1, pp. 29-35, ISSN 1582-5175.
1. Introduction
The demand of energy consumption is increasing throughout the world due to population growth, urbanization and economic development [1]. At the same time, it is expected that fossil fuel resources will be depleted [2]. Several research projects are aimed at finding alternative solutions, based on inexhaustible renewable energies to guarantee the satisfaction of the demand for electrical energy. Today, large wind turbines become competitive in terms of production costs. It is helping to reduce greenhouse gas emissions[3].
In wind energy conversion system, two types may be considered. First, the conversion system is provided from the fixed wind speed. Therefore, the generator is directly connected to the grid, from which a poor quality of power energy is derived in the grid when the wind varies [4, 5].Second, the conversion system is provided through the variable wind speed, from which the generator is before equipped with the power electronic converter and then connected to the grid. Compared to the first conversion system, the second one have many advantages such as, the better performances of the MPPT, the good decoupling system between both generating and grid frequency as well as a good flexibility is observed between them in terms of control and optimal operation[6], the better efficiency to control both mechanical stress with reduced cost [7]. In the last years, many researchers have focused on the variable speed control of wind turbines in the literature. Starting from classical controllers such as the proportional integral PI controller [8],the linear quadratic Gaussian LQG
controller [9],continuing with some modern controllers such as the generalized predictive control GPC controller for maximizing the generated power of WECS[10,11].
In this regard, the synthesis controllers based upon sliding mode control strategy have been suggested to avoid the above disadvantages. The obtained controllers have the ability of maximizing as much as possible the power of induction generator and super imposing the tracking of the optimal torque value [12,13].However, a common disadvantage of these strategies appears in the definition step of the switched component, which is followed the sign of the tip speed ratio error and yields therefore to the discontinuous sign function. To avoid this problem, several techniques have been proposed to reduce the effect of the switched component such as the saturation hyperbolic tangent and other continuous control laws, wherein the sign function is substituted [14,15]. So that, the main contribution of this paper is to introduce an additional low- frequency component in the sliding mode controller in order to maximize the extracted power and to eliminate the chattering phenomenon caused by the mechanical stress, where the performances of the standard sliding mode control are enhanced and the obtained power energy is therefore increased.
The present paper is organized as follows. In Section 2,a brief description of the proposed system with variable wind speed will be presented. In Section 3, an improved sliding mode control strategy of the wind energy conversion system and robustness analysis will be discussed in details.
In Section 5, simulation results will be proved. Finally, it is ended by a conclusions.
