Modelling Simulation and Analysis of Standalone Wind Generator

 

Shweta Agrawal¹ and S.P. Dubey²

¹M. Tech. Research Scholar, Rungta College of Engineering and Technology, Bhilai

E-mail: agrawal4shweta@gmail.com

²Professor, Department of Electrical Engineering, Rungta College of Engineering and Technology, Bhilai

E-mail: spd1020@yahoo.com

ABSTRACT:

Electricity supply industry and open access market for electricity worldwide, renewable sources are getting added into the grid system. This affects the grid power quality. To assess the impact on grid due to wind energy integration, the knowledge of electrical characteristic of wind generators and associated control equipment’s are required. The presented control scheme provides the wind power flow to the grid through a converter. The injected power in the system at the point of common coupling is ensured within the power quality norms. This paper is concerned with the transient stability of variable-speed wind generators with permanent magnet synchronous generators at a pitch control malfunction. As wind power generation undergoes rapid growth, new technical challenges emerge: dynamic stability and power quality. The influence of a pitch control malfunction on the quality of the energy injected into the electrical grid, analyzing the transient stability with different topologies for the power-electronic converters has been studied. Computer simulations obtained by using MATLAB/Simulink are presented, and conclusions are duly drawn.

 

KEYWORDS: Wind generators; grid, power supply; simulation; power quality;wind generating system.

 

I. INTRODUCTION:

Generation of electricity from wind is the fastest growing energy technology in the world. India is in the 4^th rank and has a renewable energy gross potential installed of 7855 MW as on 2006.With increasing wind power production, it is important for grid owners, to predict the grid interaction of wind turbine in advance. Some grid simulation packages like power system simulator are used for power system behavioral studies. Models of new types of generating units, like wind turbine have to comply with the requirement. Considering wind turbine generating system operation in electric power system, it is necessary to utilize the steady state model for analysis, related to load flow, short circuit calculation, power quality assessments, etc. The electric utility grid system cannot accept connection of new generation plant without strict condition, due to the real power fluctuation and reactive power generation of wind plants. Therefore the penetration of wind power in grid implies taking care of power quality issues like voltage variation on grid, switching operation of wind turbine. Today grid connected wind turbines are equipped with power converter systems.

 

Coughlan and Smith [3] discussed in his paper that power system stability describes the ability of a power system to maintain synchronism and maintain voltage when subjected to severe transient disturbances. Ullah and Thiringer [4] suggests as wind energy is increasingly integrated into power systems, the stability of already existing power systems is becoming a concern of utmost importance. Also, network operators have to ensure that consumer power quality is not compromised. Hence, the total harmonic distortion (THD) should be kept as low as possible, improving the quality of the energy injected into the electrical grid [5]. The development of power electronics and their applicability in wind energy extraction allowed for variable speed operation of the wind turbine [6]. The variable-speed wind turbines are implemented with either doubly fed induction generator (DFIG) or full-power converter. In a variable-speed wind turbine with full-power converter, the wind turbine is directly connected to the generator, which is usually a permanent magnet synchronous generator (PMSG). Harmonic emissions are recognized as a power quality problem for modern variable-speed wind turbines.

Understanding the harmonic behavior of variable-speed wind turbines is essential in order to analyze their effect on the electrical grids where they are connected [7]. Variable-speed wind turbines usually employ active pitch control, where blade pitch angle increases reduce the captured wind power by reducing the angle of attack [8]. The pitch control may have a considerable effect on the dynamical behavior of wind generators. However, previous papers were mainly focused on the transient stability of variable-speed wind turbines at external grid faults [8], [9]. This paper focuses on the transient stability of variable speed wind turbines with PMSG at a pitch control malfunction. Hence, we study the influence of a pitch control malfunction on the quality of the energy injected into the electrical grid, analyzing the transient stability with different topologies for the power-electronic converters. Additionally, we propose a new control strategy based on fractional-order controllers for the variable-speed operation of wind turbines with PMSG/full-power converter topology. The performance of disturbance attenuation and system robustness is ascertained. Computer simulations obtained by using Matlab/Simulink are presented, and conclusions are duly drawn.

Fig 15:THD of the current injected in the grid with the multilevel converter.

Table I summarizes an overall comparison between a classical PI controller and fractional-order PI^5/10 and PI^7/10 controllers, concerning the THD of the current injected in the grid.

 

TABLE: 1 THD OF THE CURRENT INJECTED IN THE GRID

 

The fractional-order controllers improve the performance of disturbance attenuation and system robustness. Also, the current THD for the wind power system with multilevel converter is much lower than the 5% limit imposed by IEEE-519 standard [19]. Although IEEE-519 standard might not be applicable in such situation, it is used as a guideline for comparison purposes [20].

 

VI. CONCLUSION:

As wind power generation undergoes rapid growth, new technical challenges emerge: dynamic stability and power quality. The novel contributions of this paper are twofold. The transient stability of variable-speed wind turbines with PMSG/full-power converter topology has been studied in this paper, considering not only wind speed disturbances, but also a pitch control malfunction. The simulation results show that the new fractional-order control strategy proposed improves the performance of disturbance attenuation and system robustness. Also, it has been shown that the current THD for the wind power system with multilevel converter is much lower than 5% limit imposed by IEEE-519 standard.

 

 

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