A Comprehensive Design Approach of Power Electronic-Based Distributed Generation Units Focused on Power quality Improvement

 

Abstract

The undesirable harmonic distortion produced by distributed generation units (DGUs) based on power electronic inverters presents operating and power quality challenges in electric systems. ‡e level of distortion depends on the internal elements of the DGUs as well as on the characteristics of the grid, loads, controls, a others. ‡is paper presents a comprehensive method, focused on power quality indexes and eciency for the design of micro-grids with multiple DGUs interconnected to the AC grid through three phase multi-Megawatt medium-voltage PWM voltage source inverters (PWM-VSI). ‡e proposed design method is based on a least square solution using the harmonic domain modeling approach to e‚ectively consider explicitly the harmonic characteristics of the DGUs and their direct and cross-coupling interaction with the grid, loads and the other DGUs. Extensive simulations and analyses against PSCAD are presented in order to show the outstanding performance of the proposed design approach.

EXISTING  SYSTEM: 

Ideal operating conditions are increasingly dicult to sustain as valid, since harmonic generation, interaction of controls and harmonic components, resonances, harmonic stability issues, etc, are phenomena commonly reported in systems with high harmonic penetration. In practical networks with power electronic-based DGUs, this could lead to erroneous or unfavorable operating scenarios. Œis gap has been recognized and addressed in the open literature, although not in a holistic way. For instance, reference deals with the power transfer capability problem of DGUs including harmonic distortion, and considering power quality regulations at a speci€c point of the network. brings out some pitfalls of electric power quality indexes allowed by international regulations showing that being within the limits is not enough in order to ensure proper performance of the DGUs electrically close to each other. In more sophisticated approaches, the power quality on the distribution system is improved by the use of harmonic compensation methods in the control schemes of the interconnected DGUs. In this way, one of the best practice to mitigate the adverse harmonic e‚ects is the proper design of the passive filters connected to the end terminals of power electronic converters. Several design methods or procedures, specially for the LCL filter, have been proposed. However, most are based on a trial and error process in which their diculty and convergence problems considerably increase for systems with multiple DGUs based on power electronic converters, specifically from medium to high power levels.

PROPOSED  SYSTEM:

Œis paper proposes a comprehensive approach, based on optimization and the extended harmonic domain (EHD), for the design of multiple grid-connected multi-MegawaŠ medium-voltage PWM-VSI with LCL €lters. Œis is carried out by means of a Nonlinear Least S‹ares formulation (NLSQ), which calculates the €lter parameters and the steady state control variables which meet certain proposed reference operating conditions and includes power quality restrictions and eciency. As an example, the design of two DGUs, based on three-phase PWM-VSIs, which are connected to a micro-grid is presented. Two case studies are presented to show the proposed design approach, one considering that the interconnections grid is unknown and the other when is known. Œe obtained results show the remarkable good performance of the proposed design approach on both cases, along with advantages over other design methodologies, which rely on the comprehensive consideration of multiple design objectives.  Conclusions Œis paper has introduced a novel design methodology based on optimization and the extended harmonic domain (EHD) for interconnected distributed generation units (DGUs) in which the harmonic distortion and its e‚ects over multiple   design objectives are explicitly considered. Œe design results of the presented case studies have shown a remarkable performance when both, the grid parameters are available and not available, o‚ering an excellent power quality with the best efficiency possible in the presence of low switching frequencies. Compared with other design methodologies, this proposal o‚ers an advanced performance, which rely on the comprehensive consideration of multiple design objectives. Acknowledgment Œe authors want to thank to the Universidad Aut ´ onoma de San Luis Potos ´ i (UASLP) through the Facultad de Ingenier ´ ia and the projects FORDECYT 190966 and FAI 2015 C15-FAI-04-106.106 for the facilities granted to carry-out this research. Miguel Esparza acknowledges the €nancial support granted by CONACYT to €nance this research.

 

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