Fuzzy Sliding Mode controls of Active and Reactive Power of a DFIG and Variable Speed Wind Energy conversion (original) (raw)
Abstract
Abstarct In this paper an indirect vector control using fuzzy sliding mode control is proposed for a double-fed induction generator (DFIG), applied for a wind energy conversion system in variable speed. The objective is to independently control the active and reactive power generated by the DFIG, which is decoupled by the orientation of the flux. The sliding mode control finds its strongest justification for the problem concerning the use of a robust nonlinear control law for the model uncertainties. As far as the fuzzy mode control is concerned, it aims at reducing the chattering effect. The obtained results show the increasing interest of such control in this system. In this study, fuzzy sliding-mode control (FSMC) method, which is one of the active control algorithms, has been applied for a double-fed induction generator (DFIG). The chattering effect, the major disadvantage of conventional sliding-mode controller, has been removed by introducing FSMC without losing the robustness against parametric uncertainties, modeling inaccuracies and varying dynamic loads. For realizing the intelligent pitch controller, fuzzy sliding mode control, which combines fuzzy sliding mode control and self-organizing modifier, is proposed. 1.Introduction In recent years, there has been an evolution of wind electrical energy production. This source of energy has developed importantly considering the diversity of the exploitable zones and the relatively beneficial cost [1]. Now most wind turbines are equipped with a double-fed induction generator (DFIG) due to noticeable advantages: the variable speed generation (±30% around the synchronous speed), the decoupled control of active and reactive powers, the reduction of mechanical stresses and acoustic noise, the improvement of the power quality, and the low cost [2]. In the literature on DFIG control, different techniques have been used, among them indirect vector control with a PI controller. This technique offers some advantages: practical implementation, protection against the DFIG currents at high intensity, and operation of the DFIG as an active filter [3]. However, this technique of control loses its robustness and performance during the exposure of the DFIG to some constraints, such as the effects of parameter uncertainties (caused by heating, saturation, etc.) and the speed variation disturbance. In addition to these drawbacks, there is also the effect of coupling between the active and the reactive power [4]. To ensure the robustness and good performance of the indirect vector control using a PI controller, several approaches have been recently proposed. In [5], the authors proposed to optimize the gains of PI controllers by the genetic algorithm. In [6] and [7], the authors proposed an adaptive control with fuzzy and neuro-fuzzy logic to adjust the gains of PI controllers. Other approaches were adopted to change the PI controllers for other controllers, namely polynomial RST based on pole placement theory and linear quadratic Gaussian [4], sliding mode [8], second-order sliding mode [9], and fuzzy logic [10].
Figures (13)
Figure 1. Wind Turbine Model A wind turbine generally consisted of a wind rotor, drive shaft, gear system and a generator, as presented in Fig. 1 [16]. The wind turbine consists of several blades (mostly three blades). The wind turbine rotates at a speed which depends on the wind speed. This speed will be adapted to that of the electric generator through a gearbox. The energy recovered by the wind turbine rotor is given by:
Figure 2. The Park Transformation. (Right Figure is (DFIG representation on a three-phase plane and left Figure is DFIG representation on a two-phase plane) In the three-phase plan, the representation of asynchronous machine is difficult because it is strongly coupled. So it is necessary to represent the machine behavior in a two-phase plane given by the transformation of Park (Fig. 2). Table 1. DFIG Parameters of Wind Turbine.
Figure 3. Sliding mode in a phase plane (s = Ae + e’) where, x is the state vector and f (x,t ), b( x,t )are nonlinear functions and u is the control input. The sliding mode control belongs to the family of a variable structure controllers. The advantage of this method is its simplicity and robustness in spite of uncertainties in the system and external disturbances. It consists of designing a control law that helps, to attract the state vector toward the sliding surface and to slide on the surface until reaching the equilibrium point (Fig. 3) [21-23]. We consider a nonlinear system defined as: x™(t) = f(x, t) + b(x, thu(x, t) (18 where. x is the state vector and f (x,t ),b( x,t )are nonlinear functions and u is the control input.
In this part, we develop a law command to control the rotational speed. Taking into account of (8) and (10), we obtain, 4.1 Wind Turbine Rotational Speed Command The use of saturation function instead of sign function is justified to avoid chattering phenomenon.
According to (18), the switching surface is given by, In this part, we develop a law command to control the stator active power. According to the first equation of (16), the quadrature currents on the rotor axis is given by: 4.2 Stator Active Power Command
The control strategy was applied to a 660-kW wind turbine using Matlab /Simulink software. The simulation results show the effectiveness of the control strategy used in this study. The parameters of the wind turbine are:
Figure 4. input and output membership of fuzzy system
Now in this section all results are shown from the calculation of the equation.
Figure 7. Output DC Voltage (Blue is FSM, Red is SM and Green is PI)
Figure 8. Current Transmission (Blue is FSM, Red is SM and Green is PI) Now Transmission current and voltage in wind turbine are shown.
Figure 9. Voltage Transmission (Blue is FSM, Red is SM and Green is PI)
Figure 10. Voltage Transmission (Blue is FSM, Red is SM and Green is PI) The turbine speed is proportional to the wind speed. The three controllers are compared with each other by varying the speed of time, with four steps of time.
In this paper, the control of a 600-kW wind turbine for low wind speed was presented. To achieve this objective, the nonlinear fuzzy sliding mode control with. The fuzzy maximum power point tracking that shown active power, reactive power and output current and voltage transmission in this controller is so better than the other controllers in this paper. MPPT is using to determine the rotational speed reference. The advantage of the proposed approach, compared to the conventional method is the good reference tracking. Simulation results show the effectiveness of the applied control strategy.
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