BDFIG as an Alternative Energy Resource Free Essay Example

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Introduction

Researchers have long been looking for alternative form of energy production driven by the environmental concerns and the operational cost. This led to an increased study on renewable form of energy in recent years[1,2]. The dynamics of these renewable forms are constantly being improved as a result its complexity increases and its control strategies are modernized[3,4]. That is why the Brushless Doubly Fed Induction Generator (BDFIG) based of Wind Energy Conversion System (WECS) has earned a significant affinity in the last few years due to his variable wind speeds operating ability which resulted in optimal power generation [5].

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The (BDFIG) Brushless Doubly Fed Induction Generator, also called the (BDFM) Brushless Doubly Fed Machine, guarantees significant benefits as a variable speed generator for wind power application as a result of its fractionally rated converter and brushless operation [6]. The reliability of the device increases and the cost of the maintenance decreases with the absence of a brush gear [7]. This configuration is difficult to reach installation and very significant for offshore.

Furthermore, the manufacturing cost of the (BDFIG) is significantly less in comparison to the doubly fed induction generator [8]. This is the result of the simple structure of the rotor winding and the absence of the slip ring system. In recent years, researchers have focused their efforts on eliminating the slip rings as well as brushes, at the same time, preserving the benefits of DFIG. The importance of these benefits increase as a result of the continuous attempt to minimize the operational and capital costs of the wind turbines in addition to enhancing their reliability.

Many BDFIG scalar control algorithms are proposed in literature. For example, it is presented that the machine can be stabilized over a wide speed range by open loop-control, closed-loop frequency control and phase-angle control. However, field-oriented control also called vector control (VC) methods, can offer better dynamic performance [9]. The latter can be applied with conventional proportional in addition to integral (PI) controller as mentioned in [5,9]. Taylor's linearization of the system dynamic model around a particular operational point is the basis of these control proposals. Therefore, the validity of the turning of the controller is restricted to a specific area. Never the less, these controllers are not robust against parameters variations, model uncertainties and external perturbations and are able to give an asymptotic convergence. Their main appeal is the rather low computational cost along with their simple implementation.

Recently, with the advancement in both technology and knowledge, various control strategies have been developed for BDFIG based WECS; for example, Feedback linearizationcontrollers, sensorlessoptimal based on extended kalman filter, vector controls and variable control strategies implementing the sliding mode control (SMC) [5-7,10,11]. Amongst the different control strategies mentioned above, the linear variable structured control also called the SMC is known to be the most qualified methods for dealing with the control of the BDFIG based WECS [11, 12]. The SMC guarantees an asymptotic stable condition for the nonlinear systems thanks to a perfect hyper plane [13,14]. Despite that, the SMC may not completely nullify the dynamics of the error function due to the significant drawback of chattering phenomenon, even after boosting the controller gains. Linearization concept was believed to be a good practice except the problems of degraded system performance and low reliability [15,16]. Concerning the control of the nonlinear systems, the theory of sliding mode control has been proved effective system uncertainties and disturbances [17,18]. Therefore, the time derivative of the control which is a higher order sliding mode control is used, the latter is both robust and considers treating the chattering case the same as the traditional SMC [19,20].

Thus, using the active and reactive power of the BDFIG, a high- order sliding mode control theory is suggested for the purpose of winding control side converter [RSC] of( the BDFIG. This procedure is employed on the higher (second) order derivative of the sliding surfaces replacing the first order time derivatives, resulting in the reduction of the chattering phenomenon [20]. The grid side converter (GSC) of the BDFIG is limited to proportional integral control.The strategy of the BDFIG based WECS control mainly consist two separate controls: (a) RSC control; (b) GSC control. In this paper, an active and reactive power of the stator of BDFIG is employed in a control winding side convertor where its input is presented for the RSC; however, the GSC is managed by traditional PI based control strategy. The suggested control strategy is based on the famous, super complicated algorithm, this latter guarantees more reliable chatter free transient response of the BDFIG parameters in comparison to the traditional PI.

This paper proposes another order sliding mode control strategy applied to a BDFIG system of wind strategy. The suggested control strategy realizes its solid argument for its insensitivity to parameters differences and the stability of the output variables. More importantly, this technique allows for controlling separately the active and reactive generated power by BDFIG.