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Online ISSN 1752-1424 Print ISSN 1752-1416

IET Renewable Power Generation

Volume 6, Issue 2, March 2012

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Volume 6, Issue 2

March 2012

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    • Binary PSO-based dynamic multi-objective model for distributed generation planning under uncertainty
      • Author(s): A. Soroudi  and  M. Afrasiab
      • Source: IET Renewable Power Generation, Volume 6, Issue 2, p. 67 –78
      • DOI:  10.1049/iet-rpg.2011.0028
      • Type: Article
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      • p. 67 –78 (12)
        This study proposes a stochastic dynamic multi-objective model for integration of distributed generations in distribution networks. The proposed model optimises three objectives, namely technical constraint dissatisfaction, costs and environmental emissions and simultaneously determines the optimal location, size and timing of investment for both distributed generation (DG) units and network components. The uncertainties of electric load, electricity price and wind power generations are taken into account using scenario modelling. A scenario reduction technique is used to reduce the computational burden of the model. The Pareto optimal solutions of the problem are found using a binary particle swarm optimisation (PSO) algorithm and finally a fuzzy satisfying method is applied to select the optimal solution considering the desires of the planner. The effectiveness of the proposed model is demonstrated by applying it to a realistic 201-node distribution network.
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      Small-signal stability of wind power system with full-load converter interfaced wind turbines
      • Author(s): T. Knüppel ; J.N. Nielsen ; K.H. Jensen ; A. Dixon ; J. Østergaard
      • Source: IET Renewable Power Generation, Volume 6, Issue 2, p. 79 –91
      • DOI:  10.1049/iet-rpg.2010.0186
      • Type: Article
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      • p. 79 –91 (13)
        Small-signal stability analysis of power system oscillations is a well-established field within power system analysis, but not much attention has yet been paid to systems with a high penetration of wind turbines (WTs) and with large wind power plants (WPPs). A comprehensive analysis is presented, which assesses the impact of full-load converter interfaced WTs on power system small-signal stability. The study is based on a seven-generator network with lightly damped inter-area modes. A detailed WT model with all grid relevant control functions is used in the study. The WT is, furthermore, equipped with a park-level WPP voltage controller and comparisons are presented. The WT model for this work is a validated dynamic model of the 3.6 MW Siemens wind power WT. The study is based on modal analysis which is complemented with the time-domain simulations on the non-linear system.
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      Parameters impact on the performance of a double-fed induction generator-based wind turbine for subsynchronous resonance control
      • Author(s): C. Zhu ; M. Hu ; Z. Wu
      • Source: IET Renewable Power Generation, Volume 6, Issue 2, p. 92 –98
      • DOI:  10.1049/iet-rpg.2010.0138
      • Type: Article
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      • p. 92 –98 (7)
        With increasing wind power in power systems, impact of subsynchronous resonance (SSR) on wind generator is of interest. This study presents the models of a double-fed induction generator (DFIG)-based wind turbine in a series-compensated network for SSR study. For DFIG (induction machine), the induction generator effect (IGE) is the most important factor of SSR. The control scheme for IGE is proposed in this study and the impact of the control parameters is also studied in detail. Eigenvalue analysis is conducted to study the impact of wind speeds, series compensation levels and control scheme on IGE phenomena. Time-domain simulations are performed in Matlab/Simulink to confirm the analysis.
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      Voltage/pitch control for maximisation and regulation of active/reactive powers in wind turbines with uncertainties
      • Author(s): Y. Guo ; S.H. Hosseini ; J.N. Jiang ; C.Y. Tang ; R.G. Ramakumar
      • Source: IET Renewable Power Generation, Volume 6, Issue 2, p. 99 –109
      • DOI:  10.1049/iet-rpg.2010.0145
      • Type: Article
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      • p. 99 –109 (11)
        This study addresses the problem of controlling a variable-speed wind turbine with a doubly fed induction generator (DFIG), modelled as an electromechanically coupled non-linear system with rotor voltages and blade pitch angle as its inputs, active and reactive powers as its outputs, and most of the aerodynamic and mechanical parameters as its uncertainties. Using a blend of linear and non-linear control strategies (including feedback linearisation, pole placement, uncertainty estimation and gradient-based potential function minimisation) as well as time-scale separation in the dynamics, the authors develop a controller that is capable of maximising the active power in the maximum power tracking (MPT) mode, regulating the active power in the power regulation (PR) mode, seamlessly switching between the two modes and simultaneously adjusting the reactive power to achieve a desired power factor. The controller consists of four cascaded components, uses realistic feedback signals, and operates without knowledge of the Cp-surface, air density, friction coefficient, and wind speed. Finally, the authors show the effectiveness of the controller via simulation with realistic wind profiles.
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      Probabilistic load flow for radial distribution networks with photovoltaic generators
      • Author(s): F.J. Ruiz-Rodriguez ; J.C. Hernández ; F. Jurado
      • Source: IET Renewable Power Generation, Volume 6, Issue 2, p. 110 –121
      • DOI:  10.1049/iet-rpg.2010.0180
      • Type: Article
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      • p. 110 –121 (12)
        In this study, analytical techniques and the Monte Carlo method were both applied to solve a probabilistic load flow in radial distribution networks with photovoltaic-distributed generation, but considering the technical constraints that apply to the networks (e.g. voltage regulation). The analytical technique used in this study combined the method of cumulants with the Gram-Charlier expansion to resolve probabilistic load flow. This was performed by modelling the loads and the photovoltaic (PV) distributed generation as random variables. For this purpose, the authors developed a new probabilistic model that took into account the random nature of solar irradiance and load. The results obtained demonstrate that this new analytical technique can be applied to keep voltages within standard limits at all load nodes of radial distribution networks with photovoltaic-distributed generation. A computational cost reduction has demonstrated that the analytical technique used in this study performed better than the Monte Carlo method. Acceptable solutions were reached with a smaller number of iterations. Convergence was thus rapidly attained with a lower computational cost than that needed with the Monte Carlo method.
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      Natural convection heat loss estimation of solar cavity receiver by incorporating a modified aperture ratio
      • Author(s): L. Xiao ; S.-Y. Wu ; Y.-R. Li
      • Source: IET Renewable Power Generation, Volume 6, Issue 2, p. 122 –128
      • DOI:  10.1049/iet-rpg.2011.0133
      • Type: Article
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      • p. 122 –128 (7)
        On the basis of the consideration of air property variation with temperature, a three-dimensional (3-D) numerical investigation has been performed to attain insight into the cavity aspect ratio on the natural convection heat loss of a cavity receiver for a high-temperature solar dish system. Temperature and velocity contours as well as the variation curves have shown that the expansion of convection zone together with the augmentation of velocity magnitude is mainly responsible for the increase in natural convection heat loss with decreasing cavity aspect ratio, that is, shallower cavity. Moreover, the dependency of natural convection heat loss on the cavity aspect ratio is related to the tilt angle. Also, a modified definition of aperture ratio has been introduced, aiming to reflect the combined impact of the cavity aspect ratio and aperture size. Finally, two correlations of Nusselt number have been proposed by incorporating the cavity aspect ratio and the newly defined modified aperture ratio, respectively.
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